Popular Science Monthly/Volume 75/September 1909/What Is a Living Animal? How Much of it Is Alive?
| WHAT IS A LIVING ANIMAL? HOW MUCH OF IT IS ALIVE? |
By Dr. A. F. A. KING
WASHINGTON, D. C.
CONSIDERING the second question first, the reply to it will depend a good deal upon education. An extremely ignorant person might answer that all parts of a living body are alive except the bones. It required some education before we medical men learned to realize, without surprise, that crude metallic bodies—bullets, pins, needles, wire sutures buried in our internal organs, nails driven into our fractured bones by surgeons, finger rings, scissors, forceps, spectacles, etc., left in the peritoneal cavity by careless operators—could remain in a human body without any immediate danger to life.
We had to learn also that large crystalline masses—the various forms of calculi—and dead fœtuses; lithopodians; even dead children at full term, both intra-and extra-uterine—could remain in a living body for several decades without any immediate danger to life. Thus we learn from these crude examples that living bodies may contain dead bodies, and dead substances of various kinds. Numerous other instances will now be considered.
The protective shells of some animals, the epidermal appendages (horns, tusks, hoofs, claws, nails, hair, wool, etc.), of others, are only alive at their proximal ends—their "roots" so-called. Their distal extremities are not living. They are products of life, but so are our coal beds, chalk cliffs, coral reefs and tortoise shell combs, but they are not alive.
If we ask, Where is the line of division between the dead and living in a cow's horn, or an elephant's tusk, we must reply, there is no such line. The transition from living to dead tissue is a gradational one. And this simple example should help to dispel the common error that everything in this world must be either dead or alive. Not so. It may be between the two: neither one or the other. Here, if anywhere, the old truism, Natura non facet saltem, deserves special recognition.
We must certainly realize that the gases, foodstuffs and excrementitious matters in the alimentary canal and the contents of the urinary bladder are not alive. Is the bile living? Bile is an excrement from the hepatic cells, the histological units of the liver, which find it necessary to discharge their toxic excreta into those minute drains, the bile ducts, and thence into the main sewer of the intestine. In thus maintaining their own normal metabolism, they save us from hepatic toxæmia. Bile is not alive.
Is milk a living substance? It is a saline solution, containing sugar and albumen. Microscopically we find it swarming with the postmortem débris of epithelium cells that have undergone fatty degeneration. It is the fatty dust into which these dead cells have crumbled that rises to the surface as cream and when amassed in the churn constitutes the butter of commerce. Milk is emphatically a dead material.
What of that milky emulsion we call chyle? We can not say it is alive in the intestine; nor does it become so in the thoracic duct, nor in the subclavian vein. Neither does mingling with the blood give it life. It is dead.
What of the blood itself? Commonly we speak of it as being "warm with life." Not so in cold-blooded animals. Again, it is referred to as the "vital fluid," the "life-blood"; and we say: "the blood is the life thereof." So it is, in the sense that we can not live without it, and if we lose it by hemorrhage we die. Nevertheless, the blood is not alive. Its corpuscles are, but the plasma in which they float is not living. This plasma is the natural habitat of the living corpuscle (much in the same way as a pond of water is the natural habitat of Amœba proteus), but it is not alive.
Can our blood corpuscles live in a dead plasma? It is not very long ago that in cases of hemorrhage we injected into the blood vessels large quantities of cow's milk; now-a-days we inject salt solution. In some cases we inject so much of these dead fluids that the quantity may exceed that of the normal blood plasma left behind after the hemorrhage. Hence we know by actual experiment, in these cases, that the larger part of the blood plasma mixture is not alive.
Furthermore, human leucocytes have been kept alive in normal salt solution outside of the body for many hours, retaining all their amoeboid and phagocytic properties; and recently in a properly prepared solution containing 3 per cent, of sodium citrate and 1 per cent, of sodium chloride, B. C. Boss has kept human leucocytes three days alive and has caused them to protrude and retract the most remarkably long pseudopodia so that they actually resembled squids, or tarantulas.[1] Thus we see a living plasma is not necessary for the blood corpuscles: they flourish in a dead one. The blood plasma is not alive.
In the days of venesection we were taught that the last act of vitality in blood when drawn from the body was its coagulation, but is this really any more a vital process than the clotting of sour milk? I think not.
In the same category with milk and blood plasma, we must place lymph, the fluids in the pleura, pericardium, peritoneum and synovial sacs, and also the cerebro-spinal fluid; none of them is alive. It might be supposed that the delicate structures of our central nervous system must at least be protected from contact with dead fluids. Not so. In cases of cerebro-spinal meningitis, we draw off the cerebro-spinal fluid and inject into the cerebro-spinal canal a curative antimeningitic serum that has stood on the shelves of its manufacturer, cold and dead, for half a year or more before being used.
In this line of thought we have reached the conclusion that the crystalline masses, gases and fluids in an animal body are none of them truly alive.
What have we left? What parts of the body do live? The histological units—the individual cells: these are the living inhabitants, in that great organic community, which constitutes a living animal.
The fluids of the body are inert plasmata designed for the maintenance, nourishment and functional integrity of these living units. The cells of the body are alive, but nothing else in it can be truly said to live.
Let us now ask: When an animal dies how much of it is dead? An ignorant person would reply: "All of it." Not so. The cells of a corpse remain alive some considerable time after the man has ceased to breathe. The cells of the liver continue their glycogenic function. Active spermatozoa have been found in the testicle, and living leucocytes in the cavities of the heart, many hours after death. The skin of a recent corpse can be successfully transplanted into a living person, as may also some of the internal organs, bones and joints. Recently one of our surgeons[2] has transplanted an entire knee joint (a healthy one) from the body of a corpse into the limb of a person from whom a diseased knee joint had been just previously removed. The case is progressing favorably.[3]
In the retrogressive phenomena of death as in the evolution of living from dead matter, the old saying of nature not making leaps, again asserts itself, and the prevalent error that everything must be either dead or alive, with no intermediate gradations, becomes pronouncedly manifest.
We now come to the question: What is a living animal? The one most marked characteristic of things that are truly alive is motion, especially locomotive auto-mobility, to which must be added growth and reproduction.
It is now generally admitted that the basis of life is electricity. The power that produces muscular motion, cell-movement, cell-division, cell union (as in fecundation), and embryological growth, is essentially a form of electro-magnetic energy, this energy being generated by the successive chemical decompositions and syntheses—the electrolytic asso ciations and dissociations of atoms and molecules—of anions and cations—in the complex phenomena of metabolism throughout the body. No nutritive change, even in a single cell, can take place without a disturbance of electric equilibrium and the development of an electric current, be it ever so diminutive. Nerve force, electricity and "vital force" are identical in so far as they are all manifestations of electromagnetic energy. Every histological unit in an animal body is a diminutive battery in which such energy is evolved. This, I think, is common knowledge, that has passed beyond the realm of theory.
Perhaps the crudest and most evident illustration of the production of electricity by animal metabolism is exhibited in the electric fishes: the torpedo, the Gymnotus (electric eel), the Malapterurus (electric catfish), the skate and others. In these forms, it is true, we find a special electric apparatus, consisting of some hundreds of columns made up of millions of superimposed plates or discs, arranged transversely to the length of the columns and separated from one another by an albuminous liquid, thus resembling a voltaic pile. The distribution, or discharge of this electric energy is controlled by nerves emanating from the medulla oblongata. Thus the animal, at will, can shock and capture its prey, and even emit charges, in some instances, sufficient to injure, and perhaps kill, even men and horses.
A more delicate method of demonstrating the identity of nerve force and electricity was shown at the last meeting of the International Congress of Electrology and Radiology held in the University of Amsterdam,[4] when Professor Salomonson, by using Einthoven's string-galvanometer (a sort of electric microscope), was able to measure, and render visible on a photographic plate, the electric current producing one contraction of a single muscle, for example, that of the quadriceps femoris during the patellary reflex. Even currents producing contractions in the cardiac muscles were exhibited. He presented on the screen a cardiogram, by which, he remarks: "Each muscular fiber of the heart has written its own sign-manual on the photographic plate." By means of this device he was able to exhibit visibly events successively occurring at intervals of one one-hundredth of a second, and electric nerve currents so small as the one ten-thousandth part of a single volt.
Now if every living animal, and every cell within it, be really an electrical machine—a generator of electro-magnetic energy—it is evident that in order to secure and use the power thus produced the apparatus must be insulated from its surroundings, otherwise the electricity would instantly escape back into the earth whence it came. All our electric machines and batteries are thus insulated.
Are animal bodies provided with this electric insulation? They are. The insulatory resistance of the bare human skin varies from 1,000 to 6,000 ohms. In many animals the insulation is increased by non-conducting hair, wool, fur, etc. And naked man finds it expedient to reinforce his own insulation by clothing of silk, satin, hair, wool, flannel and other non-conducting materials. We are exhilarated by a dry atmosphere: depressed by a damp one, because the moist air, being a conductor, carries off some of our electricity to the earth, while dry air is a more complete insulator and prevents this leakage.
Besides contact with the air, the feet of animals are in actual contact with the earth itself, and accordingly ought to be endowed with a specially good insulation.
Finding no data on this point, I submitted to the U. S. Bureau of Standards some specimens of a horse's hoof, to have their insulation tested. The director, Professor S. W. Stratton, wrote me[5] that the resistance of the first specimen, when dry, was 4,700 million ohms. This was a part of the "frog" of the foot. A second specimen, taken from the peripheral margin of the hoof was tested, of which the bureau reported[6] that "by the direct-deflection method, using 120 volts and a very sensitive galvanometer, the deflection was so small that it could not be read." "The resistance was equal to or greater than 22 billion ohms. This corresponds to a specific resistance of about ohms per centimeter cube." Professor Stratton adds: "Of course the actual resistance may be much higher, as it was too high to determine with any accuracy by this means."
Subsequently, Professor Chas. W. Mortimer, of the George Washington University, by using his Wheatstone Bridge apparatus, kindly tested for me, altogether, 67 specimens of animal and some vegetable structures, as to the insulating power of their external coverings. The specimens included the feet, claws and bills of sheep, rabbits and chickens; the fresh human umbilical cord, foetal membranes and placenta; the shell of an egg; the external coverings of fruits (oranges, apples, nuts, etc.) and of vegetables (turnips, onions, etc.).
In no instance did the external covering fail to exhibit a relatively greater resistance than the internal structure. In most of the specimens the resistance hovered about 10,000,000 ohms, some more, some less. In one instance, that of a green pea pod, the resistance of the unbroken pod was 500,000 ohms, while the external surface of the green pea itself was 10,000,000 ohms.
I did not test any cereal grains, but Mr. Lyman J. Briggs, of the Bureau of Plant Industry, U. S. Department of Agriculture, has recently ascertained that the resistance of wheat grains, varying with temperature and moisture, is somewhere between 2 million and 10,000 million ohms.[7]
It is conceivable that the grains of wheat exhumed with Egyptian mummies would scarcely have retained their germinating power after so many centuries had not nature clothed them with their insulating shells, and passing from these diminutive little lives of eggs, grains and cells, it is conceivable that this globe that we inhabit would itself become a moving sepulchre, devoid of all molecular transformations of energy, were it not for the external envelope of insulating atmosphere with which it is clothed. Without this insulation the energy of solar light and heat would no longer be transformed into things of beauty and life; but would at once be dissipated into the abysses of space and our earth would probably become as dead as the moon, which has no insulating covering, and, consequently, upon whose face, within the memory of man, no single change of feature has been observed.
In the foregoing discussion my purpose has been to lay the foundation for a modified definition of life. Every one is familiar with Spencer's definition, viz:
Life is the definite combination of heterogeneous changes, both simultaneous and successive, in correspondence with external coexistences and sequences.[8]
Never, perhaps, did human language attempt to express so much in so few words. In fact it is so condensed as to be difficult of comprehension. If the definition had been given first, few of us would ever guess that life was the thing it intended to define.
On page 80, Spencer says:
The broadest and most complete definition of life will be: the continuous adjustment of internal relations with external relations.
De Blainville said:
Life is the twofold internal movement of composition and decomposition at once general and continuous.
Criticizing this definition, Spencer remarks:
It describes not only the integrating and disintegrating processes going on in a living body, but it equally well describes those going on in a galvanic battery which also exhibits a two-fold internal movement of composition and decomposition at once general and continuous.[9]
At the time Spencer wrote (1866), biology was not sufficiently advanced for him to realize that every cell in the body really was a minute electric battery, and that the coordinate and simultaneous action of millions of these batteries made up together the living body of a complete animal.
With these preliminaries, I submit the following definition of a living being. It is this: A living body, whether a simple cell or a fully developed mammal, consists of a temporary aggregation of a limited number of material particles, call them what we may—molecules, atoms, ions, electrons—whose actions and reactions between each other, and between themselves and their environing conditions (light, temperature, air, water, food, terrestrial magnetism, gravitation, etc.) are of such a kind as to generate electro-magnetic energy, which energy is and necessarily must be secured to the use of the individual producing it, by a semi-porous limiting external envelope which provides the individual with electric insulation from its surroundings.
It is upon this external electric insulation that I desire to insist as a necessary part of everything that can truly be said to "live, move and have its being." Vain and useless indeed would be the energy generated in living bodies by the successive compositions and decompositions, the integrations and disintegrations, the electrolytic associations and disassociations of ions and electrons resulting from animal metabolism, if no arrangement had been provided by which the energy developed could be secured to the use of the individual producing it, instead of instantly flashing back to the earth whence it came, which it inevitably would do, in the absence of such insulation.
That this insulatory covering really exists, in the case of animals, eggs, seeds, etc., has been shown by the experiments before mentioned. That the individual cells of the body—the histological units—are also provided with the same electric insulation, may be more difficult to demonstrate. But such demonstration is not altogether wanting. The red corpuscles of the blood are, in a measure, insulated from the serum in which they float. "The intact red corpuscles," writes Stewart, "have an electric conductivity so many times less than that of serum that they may, in comparison, be looked upon as non-conductors."[10] Among other explanations he suggests that this may be because the envelope of the corpuscles refuses passage to the electric charge produced by the dissociation of ions within them.
In the developing ovum, according to this view, the ectoderm ought to be an insulator. I can give no proof of this, but it is significantly suggestive that the cerebro-spinal axis of the embryo (which we should think ought to receive a specially good insulation) is clothed on its outside by an investment from the ectodermic layer, produced by an invagination of that structure to form the medullary groove and canal in which the central nervous system pursues its development.
Finally, is the protoplasm of animal organisms a really living substance? The answer will depend upon our definition of the word "living." Properly speaking, protoplasm is neither dead nor alive: it is between the two.
If we could get together an ounce or a ton of it, we should say it was a substance or mass exhibiting some of the properties of living matter. We could not say it was a living individual. It is simply matter occupying a very high plane in those ascending gradational transformations between the dead and the living: between the simple inorganic constituents of the earth, and those more complex segregations of chemical atoms which finally become surrounded by a limiting insulatory envelope and thus constitute "physiological units," or living beings. But until this formation of units—this individualism—of the mass, protoplasm can not be said to live.
Of course, the direct transformation of inorganic matter into living animal matter is impossible. There must always occur the intermediate phenomenon of vegetable life. Vegetables can transform the inorganic chemical materials of the air and earth into their own structure, but the animal must either feed upon the products produced by the vegetable or upon other animals that have been so fed. No single definition of life, therefore, can include both animal and vegetable life, since the vegetable is an intermediate product between minerals and animals. The evolution of life is a gradational process. Things are not "either dead or alive." Some things, like protoplasm, are between the two.
- ↑ London Lancet, January 30, 1909, p. 314.
- ↑ Dr. Tully S. Vaughn, of Washington, D. C.
- ↑ It is now six weeks since the operation. There have been a few similar cases in Germany.
- ↑ Proceedings of the Royal Society of Medicine, November, 1908.
- ↑ Official letter, October 23, 1903.
- ↑ Official letter, January 21, 1904.
- ↑ Science, December 4, 1908, p. 812, and Bulletin 99, 1907, Bureau of Plant Industry, U. S. Department of Agriculture.
- ↑ "Principles of Biology," p. 74.
- ↑ "Principles of Biology," p. 60.
- ↑ "Human Physiology," p. 35, 3d ed., 1899.