The Body Electric
by Robert O. Becker
Introduction:
The Promise of the Art
I remember how it was before penicillin. I was a medical student at the
end of World War II, before the drug became widely available for civilian use, and I watched the wards at New York's Bellevue Hospital fill to
overflowing each winter. A veritable Byzantine city unto itself, Bellevue
sprawled over four city blocks, its smelly, antiquated buildings jammed
together at odd angles and interconnected by a rabbit warren of underground tunnels. In wartime New York, swollen with workers, sailors,
soldiers, drunks, refugees, and their diseases from all over the world, it
was perhaps the place to get an all-inclusive medical education. Bellevue's charter decreed that, no matter how full it was, every patient who
needed hospitalization had to be admitted. As a result, beds were packed
together side by side, first in the aisles, then out into the corridor. A
ward was closed only when it was physically impossible to get another
bed out of the elevator.
Most of these patients had lobar (pneumococcal) pneumonia. It didn't
take long to develop; the bacteria multiplied unchecked, spilling over
from the lungs into the bloodstream, and within three to five days of the
first symptom the crisis came. The fever rose to 104 or 105 degrees
Fahrenheit and delirium set in. At that point we had two signs to go by:
If the skin remained hot and dry, the victim would die; sweating meant
the patient would pull through. Although sulfa drugs often were effective against the milder pneumonias, the outcome in severe lobar pneumonia still depended solely on the struggle between the infection and the patient's own resistance. Confident in my new medical knowledge, I
was horrified to find that we were powerless to change the course of this
infection in any way.
It's hard for anyone who hasn't lived through the transition to realize
the change that penicillin wrought. A disease with a mortality rate near
50 percent, that killed almost a hundred thousand Americans each year,
that struck rich as well as poor and young as well as old, and against
which we'd had no defense, could suddenly be cured without fail in a
few hours by a pinch of white powder. Most doctors who have graduated
since 1950 have never even seen pneumococcal pneumonia in crisis.
Although penicillin's impact on medical practice was profound, its
impact on the philosophy of medicine was even greater. When Alexander Fleming noticed in 1928 that an accidental infestation of the mold
Penicillium notatum had killed his bacterial cultures, he made the crowning discovery of scientific medicine. Bacteriology and sanitation had already vanquished the great plagues. Now penicillin and subsequent
antibiotics defeated the last of the invisibly tiny predators.
The drugs also completed a change in medicine that had been gathering strength since the nineteenth century. Before that time, medicine
had been an art. The masterpiece—a cure—resulted from the patient's
will combined with the physician's intuition and skill in using remedies
culled from millennia of observant trial and error. In the last two centuries medicine more and more has come to be a science, or more accurately the application of one science, namely biochemistry. Medical
techniques have come to be tested as much against current concepts in
biochemistry as against their empirical results. Techniques that don't fit
such chemical concepts—even if they seem to work—have been abandoned as pseudoscientific or downright fraudulent.
At the same time and as part of the same process, life itself came to be
defined as a purely chemical phenomenon. Attempts to find a soul, a
vital spark, a subtle something that set living matter apart from the
nonliving, had failed. As our knowledge of the kaleidoscopic activity
within cells grew, life came to be seen as an array of chemical reactions,
fantastically complex but no different in kind from the simpler reactions
performed in every high school lab. It seemed logical to assume that the
ills of our chemical flesh could be cured best by the right chemical
antidote, just as penicillin wiped out bacterial invaders without harming
human cells. A few years later the decipherment of the DNA code
seemed to give such stout evidence of life's chemical basis that the double helix became one of the most hypnotic symbols of our age. It seemed
the final proof that we'd evolved through 4 billion years of chance molecular encounters, aided by no guiding principle but the changeless
properties of the atoms themselves.
The philosophical result of chemical medicine's success has been belief
in the Technological Fix. Drugs became the best or only valid treatments for all ailments. Prevention, nutrition, exercise, lifestyle, the patient's physical and mental uniqueness, environmental pollutants—all
were glossed over. Even today, after so many years and millions of dollars spent for negligible results, it's still assumed that the cure for cancer
will be a chemical that kills malignant cells without harming healthy
ones. As surgeons became more adept at repairing bodily structures or
replacing them with artificial parts, the technological faith came to include the idea that a transplanted kidney, a plastic heart valve, or a
stainless-steel-and-Teflon hip joint was just as good as the original—or
even better, because it wouldn't wear out as fast. The idea of a bionic
human was the natural outgrowth of the rapture over penicillin. If a
human is merely a chemical machine, then the ultimate human is a
robot.
No one who's seen the decline of pneumonia and a thousand other
infectious diseases, or has seen the eyes of a dying patient who's just
been given another decade by a new heart valve, will deny the benefits of
technology. But, as most advances do, this one has cost us something
irreplaceable: medicine's humanity. There's no room in technological
medicine for any presumed sanctity or uniqueness of life. There's no
need for the patient's own self-healing force nor any strategy for enhancing it. Treating a life as a chemical automaton means that it makes no
difference whether the doctor cares about—or even knows—the patient,
or whether the patient likes or trusts the doctor.
Because of what medicine left behind, we now find ourselves in a real
technological fix. The promise to humanity of a future of golden health
and extended life has turned out to be empty. Degenerative diseases—
heart attacks, arteriosclerosis, cancer, stroke, arthritis, hypertension, ulcers, and all the rest—have replaced infectious diseases as the major
enemies of life and destroyers of its quality. Modern medicine's incredible cost has put it farther than ever out of reach of the poor and now
threatens to sink the Western economies themselves. Our cures too often
have turned out to be double-edged swords, later producing a secondary
disease; then we search desperately for another cure. And the dehumanized treatment of symptoms rather than patients has alienated
many of those who can afford to pay. The result has been a sort of
medical schizophrenia in which many have forsaken establishment medicine in favor of a holistic, prescient type that too often neglects technology's real advantages but at least stresses the doctor-patient relationship, preventive care, and nature's innate recuperative power.
The failure of technological medicine is due, paradoxically, to its success, which at first seemed so overwhelming that it swept away all aspects of medicine as an art. No longer a compassionate healer working at
the bedside and using heart and hands as well as mind, the physician has
become an impersonal white-gowned ministrant who works in an office
or laboratory. Too many physicians no longer learn from their patients,
only from their professors. The breakthroughs against infections convinced the profession of its own infallibility and quickly ossified its beliefs into dogma. Life processes that were inexplicable according to
current biochemistry have been either ignored or misinterpreted. In
effect, scientific medicine abandoned the central rule of science—revision in light of new data. As a result, the constant widening of horizons
that has kept physics so vital hasn't occurred in medicine. The mechanistic assumptions behind today's medicine are left over from the turn of
the century, when science was forcing dogmatic religion to see the evidence of evolution. (The re-eruption of this same conflict today shows
that the battle against frozen thinking is never finally won.) Advances in
cybernetics, ecological and nutritional chemistry, and solid-state physics
haven't been integrated into biology. Some fields, such as parapsychology, have been closed out of mainstream scientific inquiry altogether.
Even the genetic technology that now commands such breathless admiration is based on principles unchallenged for decades and unconnected
to a broader concept of life. Medical research, which has limited itself
almost exclusively to drug therapy, might as well have been wearing
blinders for the last thirty years.
It's no wonder, then, that medical biology is afflicted with a kind of tunnel vision. We know a great deal about certain processes, such as the genetic code, the function of the nervous system in vision, muscle movement, blood clotting, and respiration on both the somatic and the cellular levels. These complex but superficial processes, however, are only the tools life uses for its survival. Most biochemists and doctors aren't much closer to the "truth" about life than we were three decades ago. As Albert Szent-Gyorgyi, the discoverer of vitamin C, has written, "We know life only by its symptoms." We understand virtually nothing about such basic life functions as pain, sleep, and the control of cell differentiation, growth, and healing. We know little about the way every organism regulates its metabolic activity in cycles attuned to the fluctuations of earth, moon, and sun. We are ignorant about nearly every aspect of consciousness, which may be broadly defined as the self : interested integrity that lets each living thing marshal its responses to eat, thrive, reproduce, and avoid danger by patterns that range from the tropisms of single cells to instinct, choice, memory, learning, individuality, and creativity in more complex life-forms. The problem of when to "pull the plug" shows that we don't even know for sure how to diagnose death. Mechanistic chemistry isn't adequate to understand these enigmas of life, and it now acts as a barrier to studying them. Erwin Chargaff, the biochemist who discovered base pairing in DNA and thus opened the way for understanding gene structure, phrased our dilemma precisely when he wrote of biology, "No other science deals in its very name with a subject that it cannot define."
Given the present climate, I've been a lucky man. I haven't been a good, efficient doctor in the modern sense. I've spent far too much time on a few incurable patients whom no one else wanted, trying to find out how our ignorance failed them. I've been able to tack against the prevailing winds of orthodoxy and indulge my passion for experiment. In so doing I've been part of a little-known research effort that has made a new start toward a definition of life.
My research began with experiments on regeneration, the ability of some animals, notably the salamander, to grow perfect replacements for parts of the body that have been destroyed. These studies, described in Part 1, led to the discovery of a hitherto unknown aspect of animal life—the existence of electrical currents in parts of the nervous system. This breakthrough in turn led to a better understanding of bone fracture healing, new possibilities for cancer research, and the hope of human regeneration—even of the heart and spinal cord—in the not too distant future, advances that are discussed in Parts 2 and 3. Finally, a knowledge of life's electrical dimension has yielded fundamental insights (considered in Part 4) into pain, healing, growth, consciousness, the nature of life itself, and the dangers of our electromagnetic technology.
I believe these discoveries presage a revolution in biology and medicine. One day they may enable the physician to control and stimulate healing at will. I believe this new knowledge will also turn medicine in the direction of greater humility, for we should see that whatever we achieve pales before the self-healing power latent in all organisms. The results set forth in the following pages have convinced me that our understanding of life will always be imperfect. I hope this realization will make medicine no less a science, yet more of an art again. Only then can it deliver its promised freedom from disease.
Part 1
Growth and
Regrowth
Salamander: energy's seed sleeping
interred in the
marrow . . .
—Octavio Paz
One
Hydra's Heads and
Medusa's Blood
There is only one health, but diseases are many. Likewise, there appears
to be one fundamental force that heals, although the myriad schools of
medicine all have their favorite ways of cajoling it into action.
Our prevailing mythology denies the existence of any such generalized
force in favor of thousands of little ones sitting on pharmacists' shelves,
each one potent against only a few ailments or even a part of one. This
system often works fairly well, especially for treatment of bacterial diseases, but it's no different in kind from earlier systems in which a specific saint or deity, presiding over a specific healing herb, had charge of
each malady and each part of the body. Modern medicine didn't spring
full-blown from the heads of Pasteur and Lister a hundred years ago.
If we go back further, we find that most medical systems have combined such specifics with a direct, unitary appeal to the same vital principle in all illnesses. The inner force can be tapped in many ways, but all
are variations of four main, overlapping patterns: faith healing, magic
healing, psychic healing, and spontaneous healing. Although science derides all four, they sometimes seem to work as well for degenerative
diseases and long-term healing as most of what Western medicine can
offer.
Faith healing creates a trance of belief in both patient and practitioner, as the latter acts as an intercessor or conduit between the sick
mortal and a presumed higher power. Since failures are usually ascribed
to a lack of faith by the patient, this brand of medicine has always been a gold mine for charlatans. When bona fide, it seems to be an escalation of
the placebo effect, which produces improvement in roughly one third of
subjects who think they're being treated but are actually being given
dummy pills in tests of new drugs. Faith healing requires even more
confidence from the patient, so the disbeliever probably can prevent a
cure and settle for the poor satisfaction of "I told you so." If even a few
of these oft-attested cases are genuine, however, the healed one suddenly
finds faith turned into certainty as the withered arm aches with unaccustomed sensation, like a starved animal waking from hibernation.
Magical healing shifts the emphasis from the patient's faith to the
doctor's trained will and occult learning. The legend of Teta, an Egyptian magician from the time of Khufu (Cheops), builder of the Great
Pyramid, can serve as an example. At the age of 110, Teta was summoned into the royal presence to demonstrate his ability to rejoin a
severed head to its body, restoring life. Khufu ordered a prisoner beheaded, but Teta discreetly suggested that he would like to confine himself to laboratory animals for the moment. So a goose was decapitated.
Its body was laid at one end of the hall, its head at the other. Teta
repeatedly pronounced his words of power, and each time, the head and
body twitched a little closer to each other, until finally the two sides of
the cut met. They quickly fused, and the bird stood up and began cackling. Some consider the legendary miracles of Jesus part of the same
ancient tradition, learned during Christ's precocious childhood in Egypt.
Whether or not we believe in the literal truth of these particular accounts, over the years so many otherwise reliable witnesses have testified
to healing "miracles" that it seems presumptuous to dismiss them all as
fabrications. Based on the material presented in this book, I suggest
Coleridge's "willing suspension of disbelief" until we understand healing better. Shamans apparently once served at least some of their patients well, and still do where they survive on the fringes of the
industrial world. Magical medicine suggests that our search for the healing power isn't so much an exploration as an act of remembering something that was once intuitively ours, a form of recall in which the
knowledge is passed on or awakened by initiation and apprenticeship to
the man or woman of power.
Sometimes, however, the secret needn't be revealed to be used. Many
psychic healers have been studied, especially in the Soviet Union, whose
gift is unconscious, unsought, and usually discovered by accident. One
who demonstrated his talents in the West was Oskar Estebany. A Hungarian Army colonel in the mid-1930s. Estebany notices that horses he
groomed got their wind back and recovered from illnesses faster than those cared for by others. He observed and used his powers informally
for years, until, forced to emigrate after the 1956 Hungarian revolution,
he settled in Canada and came to the attention of Dr. Bernard Grad, a
biologist at McGill University. Grad found that Estebany could accelerate the healing of measured skin wounds made on the backs of mice, as
compared with controls. He didn't let Estebany touch the animals, but
only place his hands near their cages, because handling itself would have
fostered healing. Estebany also speeded up the growth of barley plants
and reactivated ultraviolet-damaged samples of the stomach enzyme
trypsin in much the same way as a magnetic field, even though no
magnetic field could be detected near his body with the instruments
of that era.
The types of healing we've considered so far have trance and touch as
common factors, but some modes don't even require a healer. The spontaneous miracles at Lourdes and other religious shrines require only a
vision, fervent prayer, perhaps a momentary connection with a holy relic, and intense concentration on the diseased organ or limb. Other reports suggest that only the intense concentration is needed, the rest
being aids to that end. When Diomedes, in the fifth book of the Iliad,
dislocates Aeneas' hip with a rock, Apollo takes the Trojan hero to a
temple of healing and restores full use of his leg within minutes. Hector
later receives the same treatment after a rock in the chest fells him. We
could dismiss these accounts as the hyperbole of a great poet if Homer
weren't so realistic in other battlefield details, and if we didn't have
similar accounts of soldiers in recent wars recovering from "mortal"
wounds or fighting on while oblivious to injuries that would normally
cause excruciating pain. British Army surgeon Lieutenant Colonel H. K.
Beecher described 225 such cases in print after World War II. One
soldier at Anzio in 1943, who'd had eight ribs severed near the spine by
shrapnel, with punctures of the kidney and lung, who was turning blue
and near death, kept trying to get off his litter because he thought he
was lying on his rifle. His bleeding abated, his color returned, and the
massive wound began to heal after no treatment but an insignificant dose
of sodium amytal, a weak sedative given him because there was no morphine.
These occasional prodigies of battlefield stress strongly resemble the
ability of yogis to control pain, stop bleeding, and speedily heal wounds
with their will alone. Biofeedback research at the Menninger Foundation
and elsewhere has shown that some of this same power can be rapped in
people with no yogic training. That the will can be applied to the body's
ills has also been shown by Norman Cousing in his resolute conquest by laugh therapy of ankylosing spondylitis, a crippling disease in which
the spinal discs and ligaments solidify like bone, and by some similar
successes by users of visualization techniques to focus the mind against
cancer.
Unfortunately, no approach is a sure thing. In our ignorance, the
common denominator of all healing—even the chemical cures we profess
to understand—remains its mysteriousness. Its unpredictability has bedeviled doctors throughout history. Physicians can offer no reason why
one patient will respond to a tiny dose of a medicine that has no effect
on another patient in ten times the amount, or why some cancers go into
remission while others grow relentlessly unto death.
By whatever means, if the energy is successfully focused, it results in
a marvelous transformation. What seemed like an inexorable decline
suddenly reverses itself. Healing can almost be defined as a miracle. Instant regrowth of damaged parts and invincibility against disease are
commonplaces of the divine world. They continually appear even in
myths that have nothing to do with the theme of healing itself. Dead
Vikings went to a realm where they could savor the joys of killing all
day long, knowing their wounds would heal in time for the next day's
mayhem. Prometheus' endlessly regrowing liver was only a clever torture
arranged by Zeus so that the eagle sent as punishment for the god's
delivery of fire to mankind could feast on his most vital organ forever—
although the tale also suggests that the prehistoric Greeks knew something of the liver's ability to enlarge in compensation for damage to it.
The Hydra was adept at these offhand wonders, too. This was the
monster Hercules had to kill as his second chore for King Eurystheus.
The beast had somewhere between seven and a hundred heads, and each
time Hercules cut one off, two new ones sprouted in its place—until the
hero got the idea of having his nephew Iolaus cauterize each neck as soon
as the head hit the ground.
In the eighteenth century the Hydra's name was given to a tiny
aquatic animal having seven to twelve "heads," or tentacles, on a hollow, stalk like body, because this creature can regenerate. The mythic
Hydra remains a symbol of that ability, possessed to some degree by
most animals, including us.
Generation, life's normal transformation from seed to adult, would
seem as unearthly as regeneration if it were not so commonplace. We see
the same kinds of changes in each. The Greek hero Cadmus grows an
army by sowing the teeth of a dragon he has killed. The primeval serpent makes love to the World Egg, which hatches all the creatures of
the earth. God makes Adam from Eve's rib, or vice versa in the later
version. The Word of God commands life to unfold. The genetic words encoded in DNA spell out the unfolding. At successive but still limited
levels of understanding, each of these beliefs tries to account for the
beautifully bizarre metamorphosis. And if some savage told us of a magical worm that built a little windowless house, slept there a season, then
one day emerged and flew away as a jeweled bird, we'd laugh at such
superstition if we'd never seen a butterfly.
The healer's job has always been to release something not understood,
to remove obstructions (demons, germs, despair) between the sick patient and the force of life driving obscurely toward wholeness. The
means may be direct—the psychic methods mentioned above—or indirect: Herbs can be used to stimulate recovery; this tradition extends
from prehistoric wise women through the Greek herbal of Dioscorides
and those of Renaissance Europe, to the prevailing drug therapies of the
present. Fasting, controlled nutrition, and regulation of living habits to
avoid stress can be used to coax the latent healing force from the sick
body; we can trace this approach back from today's naturopaths to Galen
and Hippocrates. Attendants at the healing temples of ancient Greece
and Egypt worked to foster a dream in the patient that would either
start the curative process in sleep or tell what must be done on awakening. This method has gone out of style, but it must have worked fairly
well, for the temples were filled with plaques inscribed by grateful patrons who'd recovered. In fact, this mode was so esteemed that
Aesculapius, the legendary doctor who originated it, was said to have
been given two vials filled with the blood of Medusa, the snaky-haired
witch-queen killed by Perseus. Blood from her left side restored life,
while that from her right took it away—and that's as succinct a description of the tricky art of medicine as we're likely to find.
The more I consider the origins of medicine, the more I'm convinced
that all true physicians seek the same thing. The gulf between folk therapy and our own stainless-steel version is illusory. Western medicine
springs from the same roots and, in the final analysis, acts through the
same little-understood forces as its country cousins. Our doctors ignore
this kinship at their—and worse, their patients'—peril. All worthwhile
medical research and every medicine man's intuition is part of the same
quest for knowledge of the same elusive healing energy. [the intelligent way to look at life d.c ]
Failed Healing in Bone
As an orthopedic surgeon, I often pondered one particular breakdown of
that energy, my specialty's major unsolved problem—nonunion of fractures. Normally a broken bone will begin to grow together in a few weeks if the ends are held close to each other without movement. Occasionally, however, a bone will refuse to knit despite a year or more of
casts and surgery. This is a disaster for the patient and a bitter defeat for
the doctor, who must amputate the arm or leg and fit a prosthetic substitute.
Throughout this century, most biologists have been sure only chemical processes were involved in growth and healing. As a result, most
work on nonunions has concentrated on calcium metabolism and hormone relationships. Surgeons have also "freshened," or scraped, the fracture surfaces and devised ever more complicated plates and screws to
hold the bone ends rigidly in place. These approaches seemed superficial
to me. I doubted that we would ever understand the failure to heal
unless we truly understood healing itself.
When I began my research career in 1958, we already knew a lot
about the logistics of bone mending. It seemed to involve two separate
processes, one of which looked altogether different from healing elsewhere in the human body. But we lacked any idea of what set these
processes in motion and controlled them to produce a bone bridge across
the break.
STAGES OF FRACTURE HEALING
Every bone is wrapped in a layer of tough, fibrous collagen, a protein
that's a major ingredient of bone itself and also forms the connective
tissue or "glue" that fastens all our cells to each other. Underneath the
collagen envelope are the cells that produce it, right next ro the bone;
together the two layers form the periosteum. When a bone breaks, these
periosteal cells divide in a particular way. One of the daughter cells stays
where it is, while the other one migrates into the blood clot surrounding the fracture and changes into a closely related type, an osteoblast, or
bone-forming cell. These new osteoblasts build a swollen ring of bone,
called a callus, around the break.
Another repair operation is going on inside the bone, in its hollow
center, the medullary cavity. In childhood the marrow in this cavity
actively produces red and white blood cells, while in adulthood most of
the marrow turns to fat. Some active marrow cells remain, however, in
the porous convolutions of the inner surface. Around the break a new
tissue forms from the marrow cells, most readily in children and young
animals. This new tissue is unspecialized, and the marrow cells seem to
form it not by increasing their rate of division, as in the callus-forming
periosteal cells, but by reverting to a primitive, neo-embryonic state.
The unspecialized former marrow cells then change into a type of primitive cartilage cells, then into mature cartilage cells, and finally into new
bone cells to help heal the break from inside. Under a microscope, the
changes seen in cells from this internal healing area, especially from
children a week or two after the bone was broken, seem incredibly chaotic, and they look frighteningly similar to highly malignant bone-cancer cells. But in most cases their transformations are under control, and
the bone heals.
Dr. Marshall Urist, one of the great researchers in orthopedics, was to
conclude in the early 1960s that this second type of bone healing is an
evolutionary throwback, the only kind of regeneration that humans share
with all other vertebrates. Regeneration in this sense means the regrowth of a complex body part, consisting of several different kinds of
cells, in a fashion resembling the original growth of the same part in the
embryo, in which the necessary cells differentiate from simpler cells or
even from seemingly unrelated types. This process, which I'll call true
regeneration, must be distinguished from two other forms of healing.
One, sometimes considered a variety of regeneration, is physiological
repair, in which small wounds and everyday wear within a single tissue
are made good by nearby cells of the same type, which merely proliferate
to close the gap. The other kind of healing occurs when a wound is too
big for single-tissue repair but the animal lacks the true regenerative
competence to restore the damaged part. In this case the injury is simply
patched over as well as possible with collagen fibers, forming a scar.
Since true regeneration is most closely related to embryonic development
and is generally Strongest in simple animals, it may be considered the
most fundamental mode of healing.
Nonunions failed to knit, I reasoned, because they were missing
something that triggered and controlled normal healing. I'd already begun to wonder if the inner area of bone mending might be a vestige of
true regeneration. If so, it would likely show the control process in a
clearer or more basic form than the other two kinds of healing. I figured
I stood little chance of isolating a clue to it in the multilevel turmoil of a
broken bone itself, so I resolved to study regeneration alone, as it occurred in other animals.
A Fable Made Fact
Regeneration happens all the time in the plant kingdom. Certainly this
knowledge was acquired very early in mankind's history. Besides locking
up their future generations in the mysterious seed, many plants, such as
grapevines, could form a new plant from a single part of the old. Some
classical authors had an inkling of animal regeneration—Aristotle mentions that the eyes of very young swallows recover from injury, and Pliny
notes that lost "tails" of octopi and lizards regrow. However, regrowth
was thought to be almost exclusively a plant prerogative.
The great French scientist Rene Antoine Ferchault de Reaumur made
the first scientific description of animal regeneration in 1712. Reaumur
devoted all his life to the study of "insects," which at that time meant
all invertebrates, everything that was obviously "lower" than lizards,
frogs, and fish. In studies of crayfish, lobsters, and crabs, Reaumur
proved the claims of Breton fishermen that these animals could regrow
lost legs. He kept crayfish in the live-bait well of a fishing boat, removing a claw from each and observing that the amputated extremity reappeared in full anatomical detail. A tiny replica of the limb took shape
inside the shell; when the shell was discarded at the next molting season, the new limb unfolded and grew to full size.
Reaumur was one of the scientific geniuses of his time. Elected to the
Royal Academy of Sciences when only twenty-four, he went on to invent
tinned steel, Reaumur porcelain (an opaque white glass), imitation
pearls, better ways of forging iron, egg incubators, and the Reaumur
thermometer, which is still used in France. At the age of sixty-nine he
isolated gastric juice from the stomach and described its digestive function. Despite his other accomplishments, "insects" were his life's love
(he never married), and he probably was the first to conceive of the vast,
diverse population of life-forms that this term encompassed. He rediscovered the ancient royal purple dye from Murex trunculus (a marine
mollusk), and his work on spinning a fragile, filmy silk from spider
webs was translated into Manchu for the Chinese emperor. He was the first to elucidate the social life and sexually divided caste system of bees.
Due to his eclipse in later years by court-supported scientists who valued
"common sense" over observation, Reaumur's exhaustive study of ants
wasn't published until 1926. In the interim it had taken several generations of formicologists to cover the same ground, including the description of winged ants copulating in flight and proof that they aren't a
separate species but the sexual form of wingless ants. In 1734 he published the first of six volumes of his Natural History of Insects, a milestone
in biology.
Reaumur made so many contributions to science that his study of
regeneration was overlooked for decades. At that time no one really
cared what strange things these unimportant animals did. However, all
of the master's work was well known to a younger naturalist, Abraham
Trembley of Geneva, who supported himself, as did many educated men
of that time, by serving as a private tutor for sons of wealthy families. In
1740, while so employed at an estate near The Hague, in Holland,
Trembley was examining with a hand lens the small animals living in
freshwater ditches and ponds. Many had been described by Reaumur,
but Trembley chanced upon an odd new one. It was no more than a
quarter of an inch long and faintly resembled a squid, having a cylindrical body topped with a crown of tentacles. However, it was a startling green color. To Trembley, green meant vegetation, but if this was
a plant, it was a mighty peculiar one. When Trembley agitated the
water in its dish, the tentacles contracted and the body shrank down to a
nubbin, only to re-expand after a period of quiet. Strangest of all, he saw
that the creature "walked" by somersaulting end over end.
Since they had the power of locomotion, Trembley would have assumed that these creatures were animals and moved on to other observations, if he hadn't chanced to find a species colored green by symbiotic
algae. To settle the animal-plant question, he decided to cut some in
half. If they regrew, they must be plants with the unusual ability to
walk, while if they couldn't regenerate, they must be green animals.
Trembley soon entered into a world that exceeded his wildest dreams.
He divided the polyps, as he first called them, in the middle of their
stalks. He then had two short pieces of stalk, one with attached tentacles, each of which contracted down to a tiny dot. Patiently watching,
Trembley saw the two pieces later expand. The tentacle portion began to
move normally, as though it were a complete organism. The other portion lay inert and apparently dead. Something must have made Trembley continue the experiment, for he watched this motionless object for
nine days, during which nothing happened. He then noted that the cut end had sprouted three little "horns," and within a few more days the
complete crown of tentacles had been restored. Trembley now had two
complete polyps as a result of cutting one in half! However, even though
they regenerated, more observations convinced Trembley that the creatures were really animals. Not only did they move and walk, but their
arms captured tiny water fleas and moved them to the "mouth," located
in the center of the ring of tentacles, which promptly swallowed the
prey.
Trembley, then only thirty-one, decided to make sure he was right by
having the great Reaumur confirm his findings before he published them
and possibly made a fool of himself. He sent specimens and detailed
notes to Reaumur, who confirmed that this was an animal with amazing
powers of regeneration. Then he immediately read Trembley's letters
and showed his specimens to an astounded Royal Academy early in
1741. The official report called Trembley's polyp more marvelous than
the phoenix or the mythical serpent that could join together after being
cut in two, for these legendary animals could only reconstitute themselves, while the polyp could make a duplicate. Years later Reaumur was
still thunderstruck. As he wrote in Volume 6 of his series on insects,
"This is a fact that I cannot accustom myself to seeing, after having seen
and re-seen it hundreds of times."
This was just the beginning, however. Trembley's polyps performed even more wondrous feats. When cut lengthwise, each half of the stalk
healed over without a scar and proceeded to regrow the missing tentacles. Trembley minced some polyps into as many pieces as he could
manage, finding that a complete animal would regrow from each piece,
as long as it included a remnant of the central stalk. In one instance he
quartered one of the creatures, then cut each resulting polyp into three
or four pieces, until he had made fifty animals from one.
His most famous experiment was the one that led him to name his
polyp "hydra." He found that by splitting the head lengthwise, leaving
the stalk intact, he could produce one animal with two crowns of tentacles. By continuing the process he was able to get one animal with seven
heads. When Trembley lopped them off, each one regrew, just like the
mythical beast's. But nature went legend one better: Each severed head
went on to form a complete new animal as well.
Such experiments provided our first proof that entire animals can regenerate, and Trembley went on to observe that hydras could reproduce
by simple budding, a small animal appearing on the side of the stalk
and growing to full size. The implications of these discoveries were so
revolutionary that Trembley delayed publishing a full account of his
work until he'd been prodded by Reaumur and preceded in print by
several others. The sharp division between plant and animal suddenly
grew blurred, suggesting a common origin with some kind of evolution;
basic assumptions about life had to be rethought. As a result, Trembley's observations weren't enthusiastically embraced by all. They inflamed several old arguments and offended many of the old guard. In
this respect Trembley's mentor Reaumur was a most unusual scientist
for his time, and indeed tor all time. Despite his prominence, he was
ready to espouse radically new ideas and, most important, he didn't steal
the ideas of others, an all too common failing among scientists.
A furious debate was raging at the time of Trembley's announcement.
It concerned the origin of the individual - how the chicken came from the egg, for example. When scientists examined the newly laid egg,
there wasn't much there except two liquids, the white and the yolk,
neither of which had any discernible structure, let alone anything resembling a chicken.
There were two opposite theories. The older one, derived from Aristotle, held that each animal in all its complexity developed from simple
organic matter by a process called epigenesis, akin to our modern concept of cell differentiation. Unfortunately, Trembley himself was the
first person to witness cell division under the microscope, and he didn't
realize that it was the normal process by which all cells multiplied. In an
era knowing nothing of genes and so little of cells, yet beginning to
insist on logical, scientific explanations, epigenesis seemed more and
more absurd. What could possibly transform the gelatin of eggs and
sperm into a frog or a human, without invoking that tired old deus ex
machina the spirit, or inexplicable spark of life—unless the frog or person already existed in miniature inside the generative slime and merely
grew in the course of development?
The latter idea, called preformation, had been ascendant for at least
fifty years. It was so widely accepted that when the early microscopists
studied drops of semen, they dutifully reported a little man, called a
homunculus, encased in the head of each sperm - a fine example of science's capacity for self-delusion. Even Reaumur, when he failed to find
tiny butterfly wings inside caterpillars, assumed they were there but
were too small to be seen. Only a few months before Trembley began
slicing hydras, his cousin, Genevan naturalist Charles Bonnet, had
proven (in an experiment suggested by the omnipresent Reaumur) that
female aphids usually reproduced parthenogenetically (without mating).
To Bonnet this demonstrated that the tiny adult resided in the egg, and
he became the leader of the ovist preformationists.
The hydra's regeneration, and similar powers in starfish, sea anemones, and worms, put the scientific establishment on the defensive.
Reaumur had long ago realized that preformation couldn't explain how a
baby inherited traits from both father and mother. The notion of two
homunculi fusing into one seed seemed far fetched. His regrowing
crayfish claws showed that each leg would have to contain little preformed legs scattered throughout. And since a regenerated leg could be
lost and replaced many times, the proto-legs would have to be very
numerous, yet no one had ever found any.
Regeneration therefore suggested some form of epigenesis—perhaps
without a soul, however, for the hydra's anima, if it existed, was divisible along with the body and indistinguishable from it. It seemed as
though some forms of matter itself possessed the spark of life. For lack of
knowledge of cells, let alone chromosomes and genes, the epigeneticists
were unable to prove their case. Each side could only point out the
other's inconsistencies, and politics gave preformationism the edge.
No wonder nonscientists often grew impatient of the whole argument. Oliver Goldsmith and Tobias Smollett mocked the naturalists for
missing nature's grandeur in their myopic fascination with "muck-flies."
Henry Fielding lampooned the discussion in a skit about the regeneration of money. Diderot thought of hydras as composite animals, like
swarms of bees, in which each particle had a vital spark of its own, and
lightheartedly suggested there might be "human polyps" on Jupiter and
Saturn. Voltaire was derisively skeptical of attempts to infer the nature
of the soul, animal or human, from these experiments. Referring in
1768 to the regenerating heads of snails, he asked, "What happens to its
sensorium, its memory, its store of ideas, its soul, when its head has
been cut off? How does all this come back? A soul that is reborn is an
extremely curious phenomenon." Profoundly disturbed by the whole affair, for a long time he simply refused to believe in animal regeneration,
calling the hydra " a kind of small rush."
THE SALAMANDER'S NERVOUS SYSTEM
—FORERUNNER OF OURS
This early regeneration research, Spallanzani's in particular, was a
benchmark in modern biology. Gentlemanly observations buttressed by
"common sense" gave way to a more rigorous kind of examination in
which nothing was taken for granted. It had been "known" for perhaps
ten thousand years that plants could regenerate and animals couldn't. To
many zoologists, even twenty years after Trembley's initial discovery,
the few known exceptions only proved the rule, for octopi, crayfish,
hydras, worms, and snails seemed so unlike humans or the familiar
mammals that they hardly counted. The lizard, the only other vertebrate
regenerator then known, could manage no more than an imperfect tail.
But the salamander—here was an animal we could relate to! This was no
worm or snail or microscopic dot, but a four-limbed, two-eyed vertebrate that could walk and swim. While its legendary ability to withstand fire had been disproven, its body was big enough and its anatomy
similar enough to ours to be taken seriously. Scientists could no longer
assume that the underlying process had nothing to do with us. In fact,
the questions with which Spallanzani ended his first report on the salamander have haunted biologists ever since: "Is it to be hoped that
[higher animals] may acquire [the same power] by some useful dispositions? and should the flattering expectation of obtaining this advantage
for ourselves be considered entirely as chimerical?"
Two
The Embryo at the
Wound
Regeneration was largely forgotten for a century. Spallanzani had been
so thorough that little else could be learned about it with the techniques
of the time. Moreover, although his work strongly supported epigenesis,
its impact was lost because the whole debate was swallowed up in the
much larger philosophical conflict between vitalism and mechanism.
Since biology includes the study of our own essence, it's the most emotional science, and it has been the battleground for these two points of
view throughout its history. Briefly, the vitalists believed in a spirit,
called the anima or elan vital, that made living things fundamentally
different from other substances. The mechanists believed that life could
ultimately be understood in terms of the same physical and chemical
laws that governed nonliving matter, and that only ignorance of these
forces led people to invoke such hokum as a spirit. We'll take up these
issues in more detail later, but for now we need only note that the
vitalists favored epigenesis, viewed as an imposition of order on the
chaos of the egg by some intangible "vital" force. The mechanists favored formation. Since science insisted increasingly on material explanations for everything, epigenesis lost out despite the evidence of
regeneration. [that seems foolish to me d.c.]
Mechanism dominated biology more and more, but some problems
remained. The main one was the absence of the little man in the sperm.
Advances in the power and resolution of microscopes had clearly shown
that no one was there. Biologists were faced with the generative slime again, featureless goo from which, slowly and magically, an organism
appeared.
After 1850, biology began to break up into various specialties. Embryology, the study of development, was named and promoted by Darwin himself, who hoped (in vain) that it would reveal a precise history of
evolution (phylogeny) recapitulated in the growth process (ontogeny). In
the 1880s, embryology matured as an experimental science under the
leadership of two Germans, Wilhelm Roux and August Weismann.
Roux studied the stages of embryonic growth in a very restricted, mechanistic way that revealed itself even in the formal Germanic title, Entwicklungsmechanik ("developmental mechanics"), that he applied to the
whole field. Weissman, however, was more interested in how inheritance passed the instructions for embryonic form from one generation to
the next. One phenomenon—mitosis, or cell division—was basic to
both transactions. No matter how embryos grew and hereditary traits
were transferred, both processes had to be accomplished by cellular actions.
Although we're taught in high school that Robert Hooke discovered
the cell in 1665, he really discovered that cork was full of microscopic
holes, which he called cells because they looked like little rooms. The
idea that they were the basic structural units of all living things came
from Theodor Schwann, who proposed this cell theory in 1838. However, even at that late date, he didn't have a clear idea of the origin of
cells. Mitosis was unknown to him, and he wasn't too sure of the distinction between plants and animals. His theory wasn't fully accepted
until two other German biologists, F. A. Schneider and Otto Butschli,
reintroduced Schwann's concept and described mitosis in 1873.
Observations of embryogenesis soon confirmed its cellular basis. The
fertilized egg was exactly that, a seemingly unstructured single cell.
Embryonic growth occurred when the fertilized egg divided into two
other cells, which promptly divided again. Their progeny then divided,
and so on. As they proliferated, the cells also differentiated; that is, they
began to show specific characteristics of muscle, cartilage, nerve, and so
forth. The creature that resulted obviously had several increasingly complex levels of organization; however, Roux and Weismann had no alternative but to concentrate on the lowest one, the cell, and try to imagine
how the inherited material worked at that level.
Weismann proposed a theory of "determiners," specific chemical
structures coded for each cell type The fertilized egg contained all the
determiners, both in type and in number, needed to produce every cell
in the body. As cell division proceeded, the daughter cells each received half of the previous stock of determiners, until in the adult each cell
possessed only one. Muscle cells contained only the muscle determiner,
nerve cells only the one for nerves, and so on. This meant that once a cell's
function had been fixed, it could never be anything but that one kind of cell.
In one of his first experiments, published in 1888, Roux obtained
powerful support for this concept. He took fertilized frog eggs, which
were large and easy to observe, and waited until the first cell division
had occurred. He then separated the two cells of this incipient embryo,
According to the theory, each cell contained enough determiners to
make half an embryo, and that was exactly what Roux got—two half embryos. It was hard to argue with such a clear-cut result, and the
determiner theory was widely accepted. Its triumph was a climactic victory for mechanistic concept of life, as well.
One of vitalism last gasps came from the work of another German
embryologist, Hans Driesch. Initially a firm believer in Entwicklung Mechanik, Driesch later found its concepts deficient in the face of life's
continued mysteries. For example, using sea urchin eggs, he repeated
Roux's famous experiment and obtained a whole organism instead of a
half. Many other experiments convinced Driesch that life had some special innate drive, a process that went against known physical laws.
Drawing on the ancient Greek idea of the anima, he proposed a nonmaterial, vital factor that he called entelechy. The beginning of the
twentieth century wasn't a propitious time for such an idea, however,
and it wasn't popular.
Mechanics of Growth
As the nineteenth century drew to a close and the embryologists continued to struggle with the problems of inheritance, they found they
still needed a substitute for the homunculus. Weismann's determiners
worked fine for embryonic growth, but regeneration was a glaring exception, and one that didn't prove the rule. The original theory had no
provision for a limited replay of growth to replace a part lost after development was finished. Oddly enough, the solution had already been provided by a man almost totally forgotten today, Theodor Heinrich
Boveri.
Working at the University of Munich in the 1880s, Boveri discovered
almost every detail of cell division, including the chromosomes. Not
until the invention of the electron microscope did anyone add materially to his original descriptions. Boveri found that all nonsexual cells of any one species contained the same number of chromosomes. As growth proceeded by mitosis, these chromosomes split lengthwise to make two of
each so that each daughter cell then had the same number of chromosomes. The egg and sperm, dividing by a special process called
meiosis, wound up with exactly half that number, so that the fertilized
egg would start out with a full complement, half from the father and
half from the mother. He reached the obvious conclusions that the chromosomes transmitted heredity, and that each one could exchange smaller
units of itself with its counterpart from the other parent.
At first this idea wasn't well received. It was strenuously opposed by
Thomas Hunt Morgan, a respected embryologist at Columbia University
and the first American participant in this saga. Later, when Morgan
found that the results of his own experiments agreed with Boveri's, he
went on to describe chromosome structure in more detail, charting specific positions, which he called genes, for inherited characteristics. Thus
the science of genetics was born, and Morgan received the Nobel Prize
in 1933. So much for Boveri.
Although Morgan was most famous for his genetics research on fruit
flies, he got his start by studying salamander limb regeneration, about
which he made a crucial observation. He found that the new limb was
preceded by a mass of cells that appeared on the stump and resembled
the unspecialized cell mass of the early embryo. He called this structure
the blastema and later concluded that the problem of how a regenerated
limb formed was identical to the problem of how an embryo developed
from the egg.
Morgan postulated that the chromosomes and genes contained not
only the inheritable characteristics but also the code for cell differentiation. A muscle cell, for example, would be formed when the group of
genes specifying muscle were in action. This insight led directly to our
modern understanding of the process: In the earliest stages of the embryo, every gene on every chromosome is active and available to every
cell. As the organism develops, the cells form three rudimentary tissue
layers—the endoderm, which develops into the glands and viscera; the
mesoderm, which becomes the muscles, bones, and circulatory system;
and the ectoderm, which gives rise to the skin, sense organs, and nervous system. Some of the genes are already being turned off, or repressed, at this stage. As the cells differentiate into mature tissues, only
one specific set of genes stays switched on in each kind. Each set can
make only certain types of messenger ribonucleic acid (mRNA), the "executive secretary" chemical by means of which DNA "instructs" the ribosomes (the cell's protein-factory organelles) to make the particular
proteins that distinguish a nerve cell, for example, from a muscle or cartilage cell.
There's a superficial similarity between this genetic mechanism and
the old determiner theory. The crucial difference is that, instead of determiners being segregated until only one remains in each cell, the genes
are repressed until only one set remains active in each cell. However, the
entire genetic blueprint is carried by every cell nucleus.
Science is a bit like the ancient Egyptian religion, which never threw
old gods away but only tacked them onto newer deities until a bizarre
hodgepodge developed. For some strange reason, science is equally reluctant to discard worn-out theories, and, even though there was absolutely
no evidence to support it, one of Weismann's ideas was swallowed whole by the new science of genetics. This was the notion that differentiation
was still a "one-way street," that cells could never dedifferentiate, that
is, retrace their steps from a mature, specialized state to a primitive,
unspecialized form. This assumption was made despite the fact that
chromosomes now provided a plausible means for the reversal. Remember, all cells of the adult (except the egg and sperm) contain the
full array of chromosomes. All the genes are still there, even though
most of them are repressed.
It seems logical that what has been locked might also be unlocked
when new cells are needed, but this idea was fought with unbelievable
ferocity by the scientific establishment. It's difficult now to see why,
since no principle of real importance was involved, except possibly a bit
of the supremacy of the mechanistic outlook itself. The mechanists
greeted the discovery of genes and chromosomes joyfully. Here at last
was a replacement for the little man in the sperm! Perhaps it seemed
that admitting dedifferentiation would have given life too much control
over its own functions. Perhaps, once genes were considered the sole
mechanism of life, they had to work in a nice, simple, mechanical way.
As we shall see, this dogma created terrible difficulties for the study of
regeneration.
Control Problems
After Morgan's work on salamander limb regrowth early in this century,
hundreds of other experimenters studied the miracle again and again in
many kinds of animals. Their labors revealed a number of general principles, such as:
Polarity. A creature's normal relationships of front to back and top
to bottom are preserved in the regenerate.
Gradients. Regenerative ability is strongest in one area of an animal's body, gradually diminishing in all directions.
• Dominance. Some one particular section of the lost part is replaced
first, followed by the others in a fixed sequence.
• Induction. Some parts actively trigger the formation of others later
in the sequence.
• Inhibition. The presence of any particular part prevents the formation of a duplicate of itself or of other parts that come before that
part in the sequence.
All the experiments led to one unifying conclusion: The overall structure, the shape, the pattern, of any animal is as real a part of its body as
are its cells, heart, limbs, or teeth. Living things are called organisms because of the overriding importance of organization, and each part of
the pattern somehow contains the information as to what it is in relation
to the whole. The ability of this pattern to maintain itself reaches its
height in the newts, mud puppies, and other amphibians collectively
called salamanders.
The salamander, directly descended from the evolutionary prototype
of all land vertebrates, is a marvelously complex animal, almost as complicated as a human. Its forelimb is basically the same as ours. Yet all its
interrelated parts grow back in the proper order—the same interlocking
bones and muscles, all the delicate wrist bones, the coordinated fingers—and they're wired together with the proper nerve and blood vessel
connections.
The same day the limb is cut off, debris from dead cells is carried
away in the bloodstream. Then some of the intact tissue begins to die
back a short distance from the wound. During the first two or three
days, cells of the epidermis—the outer layer of skin—begin to proliferate and migrate inward, covering the wound surface. The epidermis then
thickens over the apex of the stump into a transparent tissue called the
apical cap. This stage is finished in about a week.
By then, the blastema, the little ball of undifferentiated cells described by Morgan, has started to appear beneath the apical cap. This is
the "organ" of regeneration, forming on the wound like a miniature
embryo and very similar to the embryonic limb bud that gave rise to the
leg in the first place. Its cells are totipotent, able to develop into all the
different kinds of cells needed to reconstitute the limb.
The blastema is ready in about two weeks. Even as it's forming, the
cells at its outer edge start dividing rapidly, changing the blastema's
shape to a cone and providing a steady source of raw material—new
cells—for growth. After about three weeks, the blastema cells at the
inner edge begin to differentiate into specialized types and arrange
themselves into tissues, beginning with a cartilage collar around the old
bone shaft. Other tissues then form, and the new limb—beginning with
a characteristic paddle shape that will become the hand—appears as
though out of a mist. The elbow and long parts of the limb coalesce
behind the hand, and the regrowth is complete (except for some slight
enlargement) when the four digits reappear after about eight weeks.
This process, exquisitely beautiful and seemingly simple, is full of
problems for biology. What organizes the growth? What is the control
factor? How does the blastema "know" that it must make a foreleg instead of a bind leg? (The salamander never makes a mistake.) How does
all the information about the missing parts get to these undifferentiated cells, telling them what to become, which genes to activate, what proteins to make, where to position themselves? It's as if a pile of bricks
were to spontaneously rearrange itself into a building, becoming not
only walls but windows, light sockets, steel beams, and furniture in the
process.
Answers were sought by transplanting the blastema to other positions
on the animal. The experiments only made matters worse. If the
blastema was moved within live to seven days after it first appeared, and
grafted near the hind leg, it grew into a second hind leg, even though it
came from an amputated foreleg. Well, that was okay. The body could
be divided into "spheres of influence" or "organizational territories,"
each of which contained information on the local anatomy. A blastema put into a hind-limb territory naturally became a hind limb. This was
an attractive theory, but unfounded. Exactly what did this territory consist of? No one knew. To make matters worse, it was then found that
transplantation of a slightly older blastema from a foreleg stump to a
hind-limb area produced a foreleg. The young blastema knew where it
was; the older one knew where it had been! Somehow this pinhead of
primitive cells with absolutely no distinguishing characteristics contained enough information to build a complete foreleg, no matter where
it was placed. How? We still don't know.
One attempt at an answer was the idea of a morphogenetic field,
advanced by Paul Weiss in the 1930s and developed by H. V. Bronsted
in the 1950s. Morphogenesis means "origin of form," and the field idea
was simply an attempt to get closer to the control factor by reformulating the problem.
Bronsted, a Danish biologist working on regeneration in the common
flatworms known as planarians, found that two complete heads would
form when he cut a strip from the center of a worm's front end, leaving
two side pieces of the original head. Conversely, when he grafted two
worms together side by side, their heads fused. Bronsted saw an analogy
with a match flame, which could be split by cutting the match, then
rejoined by putting the two halves side by side, and he suggested that
part of the essence of life might be the creation of some such flamelike
field. It would be like the field around a magnet except that it reflected
the magnet's internal structure and held its shape even when part of the
magnet was missing.
The idea grew out of earlier experiments by Weiss, an American embryologist, who stymied much creative research through his dogmatism
yet still made some important contributions. Regrowth clearly wasn't a
simple matter of a truncated muscle or bone growing outward to resume
its original shape. Structures that were missing entirely—the hand,
wrist, and bones of the salamander's lower forelimb, for example—also
reappeared. Weiss found that redundant parts could be inserted, but the
essential ones couldn't easily be eliminated. If an extra bone was implanted in the limb and the cut made through the two, the regenerate
contained both. However, if a bone was completely removed and the
incision allowed to heal, and the limb was then amputated through what
would have been the middle of the missing bone, the regenerate produced that bone's lower half, like a ghost regaining its substance Weiss
suggested that other tissues besides bone could somehow project a field
that included the arrangement of the bones. As a later student of regeneration, Richard Goss of Brown University, observed, "Apparently each tissue of the stump can vote to be represented in the blastema, and
some of them can even cast absentee ballots."
Any such field must be able to stimulate cells to switch various genes
on and off, that is, to change their specialization. A large body of research on embryonic development has identified various chemical inducers, compounds that stimulate neighboring cells to differentiate in a
certain fashion, producing the next type of cells needed. But these substances act only on the basis of simple diffusion; nothing in the way they
operate can account for the way the process is controlled to express the
overall pattern.
Another classic experiment helps clarify the problem. A salamander's
hand can be amputated and the wrist stump sewn to its body. The wrist
grows into the body, and nerves and blood vessels link up through the
new connection. The limb now makes a U shape, connected to the body
at both ends. It's then amputated at the shoulder to make a reversed
limb, attached to the body at the wrist and ending with a shoulder
joint. The limb then regenerates as though it had simply been cut off at
the shoulder. The resulting limb looks like this: from the body sprouts
the original wrist, forearm, elbow, upper arm, and shoulder, followed
by a new upper arm, elbow, forearm, wrist, and hand. Why doesn't the
regenerate conform to the sequence already established in this limb instead of following as closely as possible the body's pattern as a whole?
Again, what is the control factor?
Information, and a monumental amount of it, is clearly passed from
the body to the blastema. Our best method of information processing at present is the digital computer, which deals with bits of data, signals
that, in essence, say either yes or no, 1 or 0. The number of such bits
needed to fully characterize the salamander forelimb is incalculable, exceeding the capacity of all known computers operating in unison.
The question of how this information is transferred is one of the hardest problems ever tackled by scientists, and when we fully know the
answer, we'll understand not only regeneration but the entire process of
growth from egg to adult. For now, we had best, as biologists themselves have done, skip this problem and return to it after addressing
some slightly easier ones.
It seems reasonable that understanding what comes out of the blastema
would be easier if we understood what goes into it, so the other major
questions about regeneration have always been: What stimulates the
blastema to form? And where do its cells come from?
The idea that dedifferentiation was impossible led to the related belief
that all regeneration had to be the work of neoblasts, or "reserve cells"
left over from the embryo and warehoused throughout the body in a
primitive, unspecialized state. Some biological bell supposedly called
them to migrate to the stump and form the blastema. There's evidence
for such cells in hydras and flatworms, although it's now doubtful that
they fully account for regeneration in these animals. However, no one
ever found any in a salamander. In fact, as long ago as the 1930s, there
was nearly conclusive evidence that they did not exist. Nevertheless,
anti-dedifferentiation dogma and the reserve cell theory were defended
fanatically, by Weiss in particular, so that many unconvincing experiments were interpreted to "prove" that reserve cells formed the blastema. When I started out, it was very dangerous for one's career even to
suggest that mature cells might create the blastema by dedifferentiating.
Because it was so hard to imagine how a blastema could arise without
dedifferentiation, the idea later developed that perhaps cells could
partially dedifferentiate. In other words, perhaps muscle cells could become cells that looked primitive and completely unspecialized, but that
would then take up their previous lives as mature muscle cells after a
brief period of amnesia in the blastema. To fit the square peg into the
round hole, many researchers did a lot of useless work, laboriously
counting cell divisions to try to show that the muscle cells in the stump
made enough new muscle cells to supply the regenerate. The embarrassing blastema—enigmatic and completely undifferentiated was still
there.
We now know (see Chapter 6) that at least some types of cells can
revert completely to the primitive state and that such despecialization is the major, probably the only, way a blastema forms in complex animals
like a salamander.
Nerve Connections
The other major question about the blastema's origin is: What triggers
it? The best candidates for a "carrier" of the stimulus are the nerves. In
complex multicellular animals, there's no regeneration without nerve
tissue. Back in 1823, the English amateur Tweedy John Todd found
that if the nerves into a salamander's leg were cut when the amputation
was made, the limb wouldn't regrow. In fact, the stump itself shriveled
up and disappeared. However, Todd got normal regeneration when he
gave the nerves time to reconnect before severing the leg. Science wasn't
ready to make anything of his observation, but many experiments since
have confirmed it. Over a century later, Italian biologist Piera Locatelli
showed that an extra leg would grow if a nerve was rerouted so that it
ended near an intact leg. She cut the large sciatic nerve partway down
the salamander's hind leg, leaving it attached to the spinal column and
fully threading it up under the skin so that its end touched the skinnear one of the forelegs. An extra foreleg sprouted there. When she
placed the nerve end near a hind leg, an extra hind leg grew. It didn't
matter where the nerve was supposed to be; the kind of extra structure
depended on the target area. This indicated that some sort of energy
from the nerves was adapted by local conditions that determined the
pattern of what grew back.
Soon afterward, other researchers found that when they sewed full thickness skin grafts over the stumps of amputated salamander legs, the
dermis, or inner layer of the skin, acted as a barrier between the apical
cap and an essential something in the leg, thereby preventing regeneration. Even a tiny gap in the barrier, however, was enough to allow
regrowth.
In the early 1940s this discovery led S. Meryl Rose, then a young
anatomy instructor at Smith College, to surmise that the rapid formation of full-thickness skin over the stumps of adult frogs' legs might be
what prevented them from regenerating. Rose tried dipping the wounds
in saturated salt solution several times a day to prevent the dermis from
growing over the stump. It worked! Most of the frogs, whose forelimbs
he'd amputated between the elbow and wrist, replaced some of what
they'd lost. Several regrew well-formed wrist joints, and a few even began to produce one new finger. Even though the replacements were incomplete, this was a tremendously important breakthrough, the first
time any regeneration had been artificially induced in an animal normally lacking the ability. However, the dermis did grow over the
stump, so the experiment worked by some means Rose hadn't expected.
Later, other investigators showed that in normal regeneration the apical cap, minus the dermis, was important because regrowing nerve fibers
made unique connections with the epidermal cells in the first stage of
the process, before the blastema appeared. These connections are collectively called the neuro-epidermal junction (NEJ). In a series of detailed
experiments, Charles Thornton of Michigan State University cut the
nerves to salamander legs at various times before amputating the legs,
then followed the progress of the regrowing nerves. Regeneration began
only after the nerves had reached the epidermis, and it could be prevented by any barrier separating the two, or started by any breach in the
barrier. By 1954 Thornton had proved that the neuro-epidermal junction
was the one pivotal step that must occur before a blastema could form
and regeneration begin.
Shortly thereafter, Elizabeth D. Hay, an anatomist then working at
Cornell University Medical College in New York, studied the neuro-epidermal junction with an electron microscope. She found that as each nerve fiber bundle reached the end of the stump, it broke up and
each fiber went its separate way, snaking into the epidermis, which
might be five to twenty cells thick. Each nerve fiber formed a tiny bulb
at its tip, which was placed against an epidermal cell's membrane, nestling into a little pocket there. The arrangement was much like a synapse, although the microscopic structure wasn't as highly developed as
in such long-term connections.
The junction was only a bridge, however. The important question
was: What traffic crossed it?
In 1946, Lev Vladimirovich Polezhaev, young Russian biologist
then working in London, concluded a long series of experiments in
which he induced partial regeneration in adult frogs, the same success Rose had had, by pricking their limb stumps with a needle every day.
Polezhaev then found that a wide variety of irritants produced the same
effect, although none of them worked in mammals. His experiments
indicated that making the injury worse could make regeneration better,
and showed that Rose's salt-in-the-wound procedure worked by irritation rather than by preventing dermis growth.
Next, the part that nerve tissue played was clarified considerably by
Marcus Singer in a brilliant series of experiments at Harvard Medical
School from the mid-1940s to the mid-1950s. Singer first confirmed
Todd's long-forgotten work by cutting the nerves in salamander legs at
various stages of regrowth, proving that the nerves were needed only
in the first week, until the blastema was fully formed and the information transferred. After that, regeneration proceeded even if the nerves
were cut.
Recent research had found that a salamander could replace its leg if all
the motor nerves were cut, but not without the sensory nerves. Many
assumed then that the growth factor was related only to sensory nerves,
but Singer was uneasy over this conclusion: "The problem stated in advance that one or another nerve component is all important for regeneration." (Italics added.) Several facts didn't fit, however. Not only did the blastema fail to form when all nerves were cut, it didn't begin to form
even if a substantial number, but still a minority, remained. Also, a
salamander's leg would regrow with only motor nerves if extra motor
nerves from the belly were redirected into the stump. In addition, zoologists had found that the sensory nerve contained more fibers than the
motor nerve.
Singer counted for himself. In the thigh or upper arm, sensory fibers
outnumbered motor by four to one. The ratio was even larger at the
periphery. Then he cut them in various combinations in a long series of
experiments. Regeneration worked as long as the leg had about one
fourth to one third of its normal nerve supply, no matter in what combination. There seemed to be a threshold number of neurons (nerve cells)
needed for regrowth.
But it wasn't that simple. The limbs of Xenopus, a South American
frog unique in its ability to regenerate during adult life, had nerve fibers
numbering well under the threshold. So Singer started measuring neuron
size, and found that Xenopus had much bigger nerves than non-regenerating frogs. Another series of experiments verified the link: A critical
mass—about 30 percent—of the normal nerve tissue must be intact for
regeneration to ensue.
This finding made it pretty certain that whatever it was the nerves
delivered didn't come from their known function of transmitting information by nerve impulses. If nerve impulses had been involved, regeneration should have faded away gradually with greater and greater
flaws as the nerves were cut, instead of stopping abruptly when the
minimum amount no longer remained.
Singer's discovery also provided a basic explanation for the decline of
regeneration with increasing evolutionary complexity. The ratio between
body mass and total nerve tissue is about the same in most animals, but
more and more nerve became concentrated in the brain (a process called
encephalization) as animals became more complex. This diminished the
amount of nerve fiber available for stimulating regeneration in peripheral
parts, often below the critical level.
In the early 1950s, Singer applied what he'd learned to the non-regenerating adult bullfrog. Using Locatelli's method, he dissected the
sciatic nerve out of the hind leg, leaving it attached to the spinal cord,
and directed it under the skin to the foreleg amputation stump. In two
or three weeks, blastemas had formed, and the cut legs were restored to
about the same degree as in Rose's and Polezhaev's experiments.
By 1954 Singer was ready to look for a growth-inducing chemical
that was presumed to be coming from the nerves. The most promising possibility was the neurotransmitter acetylcholine, one of several compounds known to relay nerve impulses across synapses. The nerves secreted acetylcholine more abundantly than normal during blastema
formation—just when nerve supply was crucial—and its production fell
back to normal when regrowth was well under way. Singer had studied
previous failures with acetylcholine, in which experimenters had rubbed
it on the stump or injected it into the blastema. He thought these methods were too artificial, so he invented a microinfusion apparatus to release tiny amounts of acetylcholine continually, just as the nerves did. It
used a clock motor to drip the hormone slowly through a needle into the
shoulder of an anesthetized animal in which the leg nerves had been
removed. He had trouble keeping the drugged salamanders alive, so
maybe the anesthetic affected the outcome, but even the ones that survived didn't regenerate at all. The growth factor was almost certainly
not acetylcholine.
Vital Electricity
These, then, were the shoulders on which I stood in 1958 as I began to
look for the pattern-control and blastema-stimulating factors in regeneration. At that time we knew of two things that could yield some
regrowth in non-regenerators: extra nerve and extra injury. How were
they related? Luck gave me a clue.
I began my work just after the first few Sputniks, during the "missile
gap" flap. Alarmed by the unforeseen triumphs of Russian technology,
which we'd considered primitive, the government hastily began translating every Soviet scientific journal and distributing copies free to federally
funded research centers. Suddenly, the medical library at the VA Medical Center in Syracuse, where I worked, began receiving each month a
crate of Russian journals on clinical medicine and biology. Since no one
else was much interested, this bonanza was all for me.
I soon made two discoveries: The Russians were willing to follow
hunches; their researchers got government money to try the most outlandish experiments, ones that our science just knew couldn't work. Furthermore, Soviet journals published them—even if they did work. I
particularly enjoyed Biofizika, the Soviet journal of biophysics, and it
was there I encountered a paper on the "Nature of the Variation of the
Bioelectric Potentials in the Regeneration Process of Plants," by A. M.
Sinyukhin of Lomonosov State University in Moscow.
Sinyukhin began by cutting one branch from each of a series of
tomato plants. Then he took electrical measurements around the wound
as each plant healed and sent out a new shoot near the cut. He found a
negative current—a stream of electrons—flowing from the wound for
the first few days. A similar "current of injury" is emitted from all
wounds in animals. During the second week, after a callus had formed
over the wound and the new branch had begun to form, the current
became stronger and reversed its polarity to positive. The important
point wasn't the polarity—the position of the measuring electrode with
respect to a reference electrode often determines whether a current registers as positive or negative. Rather, Sinyukhin's work was significant
because he found a change in the current that seemed related to reparative
growth. Sinyukhin found a direct correlation between these orderly electrical events and biochemical changes: As the positive current increased,
cells in the area more than doubled their metabolic rate, also becoming
more acidic and producing more vitamin C than before.
Sinyukhin then applied extra current, using small batteries, to a
group of newly lopped plants, augmenting the regeneration current.
These battery-assisted plants restored their branches up to three times
faster than the control plants. The currents were very small—only 2 to 3
microamperes for five days. (An ampere is a standard unit of electric
current, and a microampere is one millionth of an ampere.) Larger
amounts of electricity killed the cells and had no growth-enhancing
effect. Moreover, the polarity had to match that normally found in the
plant. When Sinyukhin used current of the opposite polarity, nullifying the plant's own current, restitution was delayed by two or three weeks.
To American biology, however, this was all nonsense. To understand
why, we must backtrack for a while.
Luigi Galvani, an anatomy professor in the medical school at the University of Bologna who'd been studying electricity for twenty years, first
discovered the current of injury in 1794, but unfortunately he didn't
know it.
At that time, biology's main concern was the debate between vitalism
and mechanism. Vitalism, though not always called by that name, had
been the predominant concept of life since prehistoric times throughout
the world, and it formed the basis for almost all religions. It was closely
related to Socrates' and Plato's idea of supernatural "forms" or "ideals"
from which all tangible objects and creatures derived their individual
characteristics. Hippocrates adapted this idea by postulating an anima as
the essence of life. The Platonic concept evolved into the medieval philosophy of realism, whose basic tenet was that abstract universal principles were more real than sensory phenomena. Mechanism grew out of
Aristotle's less speculative rationalism, which held that universal principles were not real, being merely the names given to humanity's attempts
at making sense of the reality apprehended through the senses. Mechanism had become the foundation of science through the writings of Descartes in the previous century, although even he believed in an
"animating force" to give the machine life at the outset. By Galvani's
time, mechanism's influence was steadily growing.
Galvani was a dedicated physician, and medicine, tracing its lineage
back to tribal shamans, has always been a blend of intuition and empirical observation based on a vitalistic concept of the sanctity of life.
The vitalists had long tried—unsuccessfully—to link the strange, incorporeal phenomenon of electricity with the elan vital. This was Galvani's
main preoccupation.
One day he noticed that some frogs' legs he'd hung in a row on his
balustrade, pending his dinner, twitched whenever the breeze blew them
against the ironwork. At about the same time his wife Lucia noticed in
his laboratory that the muscles of a frog's leg contracted when an assistant happened to be touching the main nerve with a steel scalpel at
the same instant that a spark leaped from one of the electrical machines
being operated across the room. (The only type of electricity then known
was the static type, in the form of sparks from various friction devices.)
Today we know that an expanding and collapsing electric field generated
by the spark induced a momentary current in the scalpel, which stimulated the muscle, but Galvani believed that the metal railing and scalpel
had drawn forth electricity hidden in the nerves.
Galvani experimented for years with nerves from frogs' legs, connected in various circuits with several kinds of metals. He grew convinced that the vital spirit was electricity flowing through the nerves and
announced this to the Bologna Academy of Science in 1791.
Within two years, Alesandro Volta, a physicist at the University of
Padua, had proven that Galvani had in fact discovered a new kind of
electricity, a steady current rather than sparks. He'd generated a bimetallic direct current, a flow of electrons between two metals, such as
the copper hooks and iron railing of the famous balcony observation,
connected by a conducting medium—in other words, a battery. The
frogs' legs, being more or less bags of weak salt solution, were the electrolyte, or conducting medium. They were otherwise incidental, Volta
explained, and there was no such thing as Galvani's "animal electricity."
Galvani, a shy and thoroughly non-combative soul, was crushed. His
only response was an anonymous paper in 1794 describing several experiments in which frogs' legs could be made to twitch with no metal in
the circuit. In one procedure, the experimenter touched one leg nerve
with the frog's dissected-out, naked spinal cord, while holding the other
leg to complete the circuit. Here the current was true animal electricity,
coming from the amputation wound at the base of the leg.
In the long run, Galvani unwittingly helped the cause of the mechanists by giving them something to attack. As long as the elan vital was
ephemeral, all you could say was that you couldn't find it. Once Galvani
said it was electricity, a detectable, measurable entity, there was a target
for experimentation. Actually, Baron Alexander von Humboldt, the explorer-naturalist who founded geology, proved in 1797 that Volta and
Galvani were both partly right. Bimetallic currents were real, but so was
spontaneous electricity from injured flesh. However, the mechanists had
the upper hand; Galvani's anonymous report and Humboldt's confirmation were overlooked. Galvani himself died penniless and brokenhearted in 1798, soon after his home and property were confiscated
by the invading French, while Volta grew famous developing his storage
batteries under the auspices of Napoleon.
Then in the 1830s a professor of physics at Pisa, Carlo Matteucci,
using the newly invented galvanometer, which could measure fairly
small direct currents, came up with other evidence for animal electricity.
In a meticulous series of experiments lasting thirty-five years, he conclusively proved that the current of injury was real. However, he didn't
find it in the nervous system, only emanating from the wound surface,
so it couldn't be firmly related to the vital force.
The tale took another turn in the 1840s when Emil Du BoisReymond, a physiology student in Berlin, read Matteucci's work. Du
Bois-Reymond went on to show that when a nerve was stimulated, an
impulse traveled along it. He measured the impulse electrically and announced his conclusion that it was a mass of "electromotive particles,"
like a current in a wire. Immediately he squared his shoulders, expecting
the mantle of glory to descend: "If I do not greatly deceive myself," he
wrote, "I have succeeded in realizing in full actuality . . . the hundred
years' dream of physicists and physiologists, to wit, the identity of the
nervous principle with electricity." But he had deceived himself. Soon it
was learned that the impulse traveled too slowly to be a current, and
that nerves didn't have the proper insulation or resistance to conduct
one, anyway. Any true current the size of the small measured impulse
wouldn't have made it through even a short nerve.
Julius Bernstein, a brilliant student of Du Bois-Reymond, resolved
the impasse in 1868 with his hypothesis of the "action potential." The
impulse wasn't a current, Bernstein said. It was a disturbance in the
ionic properties of the membrane, and it was this perturbation that traveled along the nerve fiber, or axon.
The Bernstein hypothesis stated that the membrane could selectively
filter ions of different charges to the inside or outside of the cell. (Ions are charged particles into which a salt breaks up when dissolved in
water; all salts dissociate in water into positive and negative ions, such
as the positive sodium and negative chloride ions of table salt.) Bernstein
postulated that the membrane could sort most of the negatives outside
and most of the positives inside the fiber. The membrane was polarized
(with like charges grouped on one side), having a transmembrane potential, because the negative charges, all on one side, could potentially flow
in a current across the membrane to achieve a balance on both sides.
This was what happened in a short segment of the membrane whenever a
nerve was stimulated. Part of the membrane became depolarized, reversing the transmembrane potential. The nerve impulse was actually a disturbance in the potential traveling along the membrane. As the area of
disturbance moved along, the membrane quickly restored its normal
resting potential. Thus the nerve impulse wasn't an electrical current,
even though it could be measured electrically.
Bernstein's hypothesis has been confirmed in all important respects,
although it remains I hypothesis because no one has yet found what
gives the membrane the energy to pump all those ions back and forth.
Soon it was broadened, however, to include an explanation of the current
of injury. Reasoning that all cells had transmembrane potentials, Bernstein maintained that, after injury, the damaged ceil membranes simply
leaked their ions out into the environment. Thus the current of injury
was no longer a sign that electricity was central to life, but only an
uninteresting side effect of cell damage.
The vitalists, with their hopes pinned on electricity, kept getting
pushed into tighter and tighter corners as electricity was removed from
one part of the body after another. Their last stand occurred with the
discovery of neurotransmitters. They'd maintained that only an electrical
current could jump across the synapse, the gap between communicating
nerves. In 1920 that idea was disproven with a lovely experiment by
Otto Loewi, a research professor at the NYU School of Medicine, later
my alma mater. When I took physiology in my first year there, we had
to duplicate his experiment.
Biologists had found that a frog heart would continue to beat for
several days when removed with its nerves and placed in an appropriate
solution. Stimulating one of the nerves would slow it down. Like Loewi,
we took one such heart, with nerve attached, and stimulated the nerve,
slowing the beat. We then collected the solution bathing that heart and
placed another heart in it. Its beat slowed even though its depressor
nerve hadn't been stimulated. Obviously the nerve slowed the heartbeat
by producing a chemical, which crossed the gap between the nerve ending and the muscle fiber. This chemical was later identified as acetylcholine, and Loewi was awarded the Nobel Prize in 1936 for this
discovery. His work resulted in the collapse of the last vestige of electrical vitalism. Thereafter, every function of the nervous system had to
be explained on the basis of the Bernstein hypothesis and chemical transmission across the synapse.
It was with great trepidation, therefore, that I put any credence in
Sinyukhin's report that the strength of the injury current affected regeneration in his plants. Yet his report was detailed and carefully written. Something about his work gave me a gut feeling that it was valid.
Maybe it was because the tomato plants he used were "Best of All"
American Beauties. At this point I wasn't aware of Matteucci's forgotten
work, but something clicked in my mind now as I studied Rose's and
Polezhaev's experiments. In both, definitely in Polezhaev's and probably
in Rose's, regeneration had been stimulated by an increase in the injury.
Then another Russian supplied a timely lead. In a government translation I found a 1958 paper by A. V. Zhirmunskii of the Institute of
Cytology in Leningrad, who studied the current of injury in the hind leg
muscle of the bullfrog. This muscle is nice and long, easy to work with,
and contains branches from several different nerves. He made a standard
injury in each muscle, measured the current of injury, then cut the
nerves branch by branch, noting the effect on the current. It decreased
with each succeeding nerve cut. The current of injury was proportional
to the amount of nerve.
Then I went to the library and delved back into the history of neurophysiology and found Matteucci's superb series of observations. Not
only had he proven that the current of injury was real, he'd shown that
it varied in proportion to the severity of the wound.
Now I had enough pieces to start on the puzzle. I summarized the
observations in a little matrix:
Extent of injury is proportional to regeneration
Amount of nerve is proportional to regeneration
Extent of injury is proportional to current of injury
Amount of nerve is proportional to current of injury
Ergo: current of injury is proportional to regeneration
I was pretty sure now chat, contemporary "knowledge" to the contrary,
the current of injury was no side effect and was the first place to look for
clues to the growth control and dedifferentiation-stimulating factors. I
planned my first experiment.
next-54s
The Sign of the
Miracle
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