Ernest G. Martin - Physiology: The Science of the Body

W HEN Alexander Pope wrote The proper study of mankind is man, he was thinking rather of man as a social being than as the possessor of an amazingly complex and interesting body. It is nevertheless true that to one who finds enjoyment in the study of intricate mechanisms or to one for whom that amazing sequence of events which we call life has appeal there is no more fascinating study than the study of the living body. That part of the study of the body which concerns itself primarily with activity and only secondarily with form and structure, makes up the science of Physiology. The way the body works is the central theme.

The practical value of Physiology to the general reader lies in the fact that it forms the basis of all sound rules of hygiene. Life is made up of bodily activities which may be carried on correctly or incorrectly. Carried on correctly they mean health, carried on incorrectly, unhealth. The world is flooded with health-preserving or health-restoring systems, urged upon the public, for the most part, by promoters in search of gain. Such of these as have merit are based on definite physiological principles, and anyone who has a common-sense working knowledge of his own body can order his life in accordance with them, at little or no expense. Moreover, a sound appreciation of Physiology drives home the truth that when the body is really out of order its restoration can be safely intrusted only to the properly trained physician: the man or woman who through years of painstaking study has won insight into the intricacies of the human mechanism and whose honest appreciation of the difficulties of his profession, and courageous sincerity in grappling with them, justify to the full the confidence in which he is held by his community.

Ernest G. Martin.

P HYSIOLOGY is the study of living things, so the first thing to be asked when we begin to think about physiology is how we are to know whether anything is alive or not. It is usually pretty easy to tell whether a dog or cat is alive or dead, although sometimes when a dog is stretched out on the road we have to look closely to tell whether he has already met his end or is merely courting it by sleeping in the public highway. There are in the world hosts of animals with which we are not familiar, and to tell whether these are alive or dead is often a puzzle. More than one picnicker has been thoroughly surprised by seeing what looked like a bit of dead twig begin to walk away, and recognized the walking stick. On the whole we will agree that the sign of life which we find most reliable is motion of some sort on the part of the living animal. If the stretched-out dog makes breathing movements, we pronounce him alive; if not, we decide that he is dead. It is because the walking stick moves off when disturbed that we know it is not a twig. But while motion is the thing we look for in living animals we know perfectly well that it would be foolish to assert that anything that moves is alive. When the wind is blowing the air may be full of dead leaves and butterflies, all moving, but only part, the butterflies, alive. Unless the motion is produced by the animal itself it is not good as a sign of life. So widespread among animals is the making of movements, either on their own account, or when disturbed, that we shall not often find ourselves mistaken if we decide that an object which remains quiet indefinitely is not a living animal. Now how about the other side of the question? Is anything that moves on its own account or when disturbed to be judged alive?

Suppose that the inhabitants of Mars have finally succeeded in perfecting a flying boat that can be hermetically sealed and shot across space from that planet to our earth. Suppose further, that the first exploring party has set forth on a voyage of discovery, and has reached a point high in our sky from which objects on the earths surface begin to be distinguishable. Of course the huge landmarks, cities, lakes, and rivers, have been in view for a long while, and now the explorers are on the lookout for signs of living things. They are watching, just as we would be, for moving objects. The first moving thing that they see will probably be a train, and we can imagine their speculations as to whether they are actually looking or not at an inhabitant of the earth. As their craft sinks toward the surface the make-up of the train becomes perceptible as also the fact that it runs on rails, showing that it is a mechanical contrivance and not a living being. As smaller objects come into view black, shiny specks are seen moving about. These show every appearance of life; they start and stop; pass each other without interference; in fact conduct themselves about as animals usually do. If their apparent great power has the effect of discouraging the exploring party, so that they give up further investigation and fly away to Mars, the inhabitants of that planet will always suppose the earth to be populated by automobiles. We know that automobiles are not alive, yet, as this little allegory shows, they behave enough like living beings to deceive distant observers. There must be some sign of life which will apply to an animal and not to an automobile; what is it? Evidently what the Martian explorers missed was the fact that the automobile does not really start or stop itself, or guide itself past obstructions. If it had been alive, it would have done these things of itself. It is not so much the power of motion, then, that proves that the thing is alive as the power of making motions that are under the control of the animal itself.

The sight of an automobile which is not alive behaving as though it were because it is under control of a driver who is alive may lead us to ask whether the animal that we know to be living is actually alive in all its parts, or is a dead mechanism of some sort which has somewhere within it a living controller, corresponding to the living driver of the car. The animals with which we are most familiar are ourselves; how is it with our own bodies? Are they alive in all their parts, or is the brain the only part of us which is living? When a patient goes under ether on the operating table, or even when he is sound asleep, the signs of life are not conspicuously present; the heart goes on beating, to be sure, but so does the engine of an automobile go on running when the driver is away, provided he has not shut it off. A favorite belief among the Hindus is that when they go into a trance the body actually becomes lifeless while the living spirit soars among the heights. How are we to decide whether the Hindus are right or not? Evidently we shall have to look deeper than we have thus far, and learn something of what is actually going on in the different parts of our bodies when we are asleep and when we are awake.

Nearly everyone learns in school the main facts about the construction of the body; that there is a bony skeleton which supports the softer parts; that motions are made by muscles; that sense organs inform us as to what is going on in the world around; that the brain is the seat of the mind; that heart, lungs, stomach, kidneys, and other organs contribute in various ways to our well-being. Not so many go into detail as to the make-up of these organs, or into the way in which they do their work. This is not a simple matter, for several reasons. The first is that the construction units are so tiny that they cannot be seen by the unaided eye, but must be studied under the high magnification of a first-class microscope. It is much harder to make out the manner of the working of tiny pieces of machinery than of those that are of convenient size. When the parts are as small as those that make up our bodies, the task of finding out how they operate is so difficult that even now, after years of study, there are many details about which we know very little.