Adaptations

( Originally Published 1909 )

PROFESSOR E. B. WILSON says, " What-ever position we take, the same difficulty is encountered, namely, the origin of that coordinated fitness, that power of active adjustment between internal and external relations, which, as so many eminent biological thinkers have insisted, overshadows every manifestation of life."

They might well say so.

The word fitness at once suggests mechanism. The different parts of a watch would not make a watch unless they were made to fit into each other. The same holds true if it be a living mechanism. Moreover, it is not the materials out of which this mechanism is composed which make it a mechanism. Very far from it. We might reduce a watch to powder with-out the least loss of its materials, but then we would not have the watch any more. So a living mechanism is not the same with its component materials, but justifies our speaking of it as a living mechanism only when its parts are adjusted to each other with a fitness which is beyond that of any non-living mechanism in the world. We shall see that there is no fitness like a living fitness.

A great steam engine, for example, is not near as complex, nor does it require a tithe of the adjustments of its parts with one another, which are necessary in a human eyelid. Not counting the lachrymal gland and its appendages, an eyelid of ours is anatomically made up of at least forty-eight different structures and special arrangements of tissues, any one of which, if it did not fit in with the rest, would give trouble. Thus the two eyelids are kept in shape in a totally different way from the two lips of the mouth, by a peculiar ring which for long was mistakenly supposed to be cartilaginous, whereas it does not have a cartilage cell in it, but instead is made of two plates of denser fibrous tissue than is found any-where else in the body. Then it would be unfortunate if the plate in the lower eyelid were of the same size and shape as that of the upper eyelid. For one thing it would disfigure a lady more than the worst squint. Nor would it do if there were as many eyelashes near the inner angle of the eye as at the other end ; nor if the eyelashes of the upper lid were not more numerous and longer than those of the lower lid,' and more than all, if those of the upper lid did not curve up and those of the lower lid curve down. To make these hairs grow that way and not like the hairs of the eyebrows or those of any other part, a special arrangement of the cells at their roots had to be provided. Then to keep the eyelids from sticking together in sleep, appear rows of twenty to thirty very peculiar glands composed of straight tubes with buds, on their sides, and secreting in their special cells an oily substance different in chemical composition from any other secretion, etc., etc.

Such are the visible structures of an eyelid, but, as every medical student knows to his sorrow, the microscope has more than quadrupled the number of facts which he must learn about the structures of organs, all of which have to do with fitness. In the case of the eyelid he may well add facts about the beginning of eye-lids in both human and in comparative embryology.

But to stop in the consideration of adaptations at an eyelid, and not pass on to the Eye itself, would be like a tourist failing to go beyond the railroad station Of the great city which he had reached. There is scarcely a tissue of the body which is not represented in the eye, besides a number of others not found elsewhere, and if we include the connections of the eye with the brain, the number and variety of its specific adaptations well-nigh exceed computation. Darwin is reported to have said that the eye made him shudder when he thought of accounting for it by Natural Selection. Now the radical difficulty with natural selection is that it cannot produce anything, nor originate anything, least of all produce an adaptation, whether simple or complex. All it can do is to select and perpetuate an adaptation already made. When a housewife picks out of a barrel the apples which are beginning to rot, her selection has not produced a single one of the sound apples which remain. But this difficulty about the eye is not lessened by the fact that some of the earliest and generally simpler animal forms nevertheless had extraordinarily complex eyes. Some creatures living in the darkness of the ocean depths provide themselves with what are virtually lanterns to help their eyes out.. This means that life has no limits in her ways for helping functions. But where no seeing is possible, life gives up the useless at-tempt and bids the fishes in the under-ground rivers of the Mammoth Cave to go without eyes. This may be called a negative adaptation, the opposite of that of the eagle's eyes as he soars towards the sun.

However, we need not dwell longer upon this instance of a living mechanism which in a small space shows more examples of fitness in adaptation than the whole world of human mechanical devices, and proceed to what seem to be much simpler arrangements for doing special work. Thus as to the intake of oxygen and the outgo of carbonic acid in breathing. Professor Haldane, whose researches on this subject are highly rated, remarks: " Liebig believed that the rate of respiratory change was regulated by the supply to the body of oxygen and of food material. If one breathed faster, the respiratory exchange was assumed to be also increased, just as ordinary combustion outside the body would be increased by an increased supply of oxygen. If, again, one took more food, it was supposed that the excess went to increase the rate of combustion in the blood, just as a fire is increased when more fuel is supplied. We now know that these assumptions were wholly mistaken, and that the respiratory movements, respiratory exchange, and corresponding consumption of food material in the body are regulated with astounding exactitude in accordance with bodily requirements. If, for instance, the body consumes more proteid, it economizes a quantity of fat and of carbohydrate equivalent in energy value to the proteid, so that from day to day the amount of energy liberated in the body is very steady." In other words, the body adjusts its chemistry just as it adjusts everything else.

The heat of the body is also kept up by chemical processes, but for that purpose more internal arrangements and adjustments to external conditions have to be in incessant operation than in the case of respiration. Even to enumerate them would require many pages, and more pages still to explain them. Thus the human body maintains just the same temperature, whether it be on the shores of the Arctic Ocean or in the hottest regions of the world. The Esquimaux live where, during the long winter, the air is from 128 to 148 degrees colder than their blood, while the people of Zanzibar live for months where the air they breathe is 20 degrees warmer than their blood. More than a hundred years ago Dr. Blagden, president of the Royal Society, and Dr. Fordyce, F.R.S., stayed for twenty minutes in heated ovens which cooked a beef-steak in 13 minutes, without the normal heat of their blood meanwhile varying in the least. They reported that their watch chains were then too hot to touch, while the air which they exhaled from their lungs felt refreshingly cool.

Nothing, indeed, but internal derangements can change the normal temperature of the blood, and hence the value of the clinical thermometer in disease. But to explain fever itself pathologists have labored and experimented for years on account of the complexity of the problems they encounter. One result is curious, and that is that fever is a good thing to have under the circumstances. Professor W. G. MacCallum of Johns Hopkins University says : " It seems probable that every detail of this fever reaction is that which is best calculated to take its own special part in the making up of a whole well-ordered plan. The conclusion seems inevitable that this plan is one devised for the good of the organism and that fever in its essentials is a protective reaction."

It will be noted that biological investigators can hardly escape from using language about living processes which imply design and purpose. The celebrated physiologist, Sir Michael Foster, when asked once why a certain physiological fact was so, replied, " Because it wants to be so!"

If we did not prolong the consideration of the adaptations of part to part in the Eye, because the reader's patience would be exhausted long before they were all enumerated, what are we to do with the Nervous System? An old anatomist well said, the nervous system is the animal. He is all there, to be sure, with more special adjustments in his nervous make-up than in all the rest of his body. In fact its illustrations of marvellous fitnesses are altogether too many for us, and so we will leave the nervous system and allude, in conclusion, to the place which one of four mysterious organs has in the ordering of our physical life. These four organs, the Pituitary, the Thyroid, the Islands of Langerhans, and the Adrenal Glands, pass directly. into the blood and not through ducts, peculiar substances which are very necessary to life. The pituitary gland is a small affair from five to ten grains in weight, only its anterior half being of much account, and its resting place is in the sella turcica or Turkish saddle-like depression in the most solid bone in the body, at the base of the skull. Disease of this gland has been supposed to be the cause of those fearful deformities in the growth of the skull and of other bony structures to which the name acromegaly has been given. That it has important relations to bodily nutrition can-not be doubted, because its experimental excision leads in time to death with very characteristic symptoms. But as its physiological mysteries have not yet been fully solved, we must await their future demonstration. The thyroid also we omit, because more than two thousand books and articles have been published so far on Graves' Disease, which most writers, but not myself,* regard as a disease of this gland. For occasioning unending discussion, the thyroid in medicine is like the tariff in politics, and so we pass on to take up the Islands of Langerhans.

The Islands of Langerhans are peculiar gland structures imbedded in the pancreas and which add to the blood an internal secretion of their own wholly distinct from the secretion of the pancreas itself, which flows off to the intestine through its duct. Disease of these islands causes bread, the staff of life, to become highly poisonous, because such disease causes that mortal derangement, diabetes. But a most peculiar fact is that if a collection of cells from these islands, not larger than a pea, be engrafted in another part of the body where they will grow, no diabetes will follow, though the pancreas itself be re-moved. We can guess from this why diabetes is the most insoluble problem in medicine.

We now pass on to take up the adrenals, those small organs whose experimental removal kills much more quickly than the removal of the kidneys themselves.

For the nervous system to make glands seems rather a come down, to be justified only by the high and important rank of the structures so originated. But we may expect anything out of the way in the performances of the Great Sympathetic, that third great nervous system in us which we know to be more closely related to our vitality than the spinal cord and the brain put together. But so mysterious are the doings of the Great Sympathetic that physicians do not often mention it because they know so little for certain about it, except that it holds very important relations to the chemistry of the living body, while to its nerves is committed the great office of regulating the supply of the blood to every part as it is needed. Thus the stomach needs about nine times more blood when it is digesting than when it is empty. As food enters it, its vasomotor nerves as they are called, which ramify on the coats of the arteries and which are derived from the sympathetic, relax the stomach arteries to flush all its secreting glands, and then when it is empty they shut the supply off. Without this incessant nervous regulation of the blood-vessels we should soon cease to live, because were the great arteries in the abdomen to relax they could hold all the blood of the body. This sometimes occurs with a quickly fatal result. Hence we are always uncomfortable if these sympathetic nerves are irregular in their duty. Thus a, sunstroke so injures the sympathetic in the neck that for years the patient's head and face flush on the slightest provocation. Now these vasomotor nerves lose all power to regulate the arteries if the adrenal glands are out of commission. And the reason seems to be this: That early in embryonic life a twig of the renal (kidney) plexus of the sympathetic becomes rolled on itself like a ball of twine. In time it breaks off from its parent stem, and, becoming enclosed in a capsule, adheres to the top of the kidney as a fully formed adrenal gland. The marvellous thing then is that these adrenals add an internal secretion to the blood, which contains a definite chemical substance which combines with acids and forms salts, and is called adrenalin. This adrenalin is virtually a drug, and as it has been isolated, it is sold over the counter like any other drug or medicine, because it has many properties of much value to the physician. It is also very powerful, for only one eight-hundredth of a grain of it will uncomfortably raise the pressure of the blood in all the arteries of the body. Now for our present purpose, the fact is interesting to state that if the adrenals are cut out, one cause for the rapid supervention of death is from paralysis of all the vasomotor nerves. Those nerves cannot act if there be no adrenalin in the blood.

Moreover, chronic disease of the adrenals causes a fatal affection called Addison's Disease, the patients finally dying from pure weakness. A strange bronzing of the skin in large patches also generally accompanies this complaint, which points to its connection with derangement of the sympathetic. Three patients with Addison's disease I have kept for a number of years from succumbing to it, by daily doses of extracts of the adrenals of sheep. Here, therefore, is another adaptation, which would make all the other numberless adaptations useless if it alone were wanting.

In the foregoing brief review we have merely given examples, out of any number of others, of adaptations in the living body, by far the most of which, if they failed to fit perfectly, would involve death. No satisfactory account of the origin of any of them has yet been given. On this one subject of adaptation the words of Professor Kellogg may well apply, " We are ignorant, terribly, immensely ignorant." * But he sensibly adds, " Our work is to learn, to observe, to experiment, to tabulate, to induce, to deduce." They must all occur according to natural laws, and to investigate the operations of natural laws is the great and honorable province of Science, because she deals with facts or with reasoning based only on facts. But in such an infinitely complex problem, more so than any in physics, chemistry, astronomy, or in any other science, it is no discredit to the learners that they still have so much more to learn. One might as well reprimand a young class not through with their primers, because they could not read and forthwith interpret one of Browning's poetical conundrums in his Rienzi.