Also, when disease is present, under the more prevalent methods, feeding is continuous in accordance with the doctrine that nourishment is at all times necessary to "keep up strength." If the stomach rebel, other organs are assailed with the idea of conveying through them the nutriment considered necessary, and this in spite of very evident protests on the part of bodily function. The question naturally suggests itself: why, if food is constantly supplied, does the body lose in weight! This query was covered in a previous chapter, but its answer is found in the fact that in disease intake of food is not properly digested, is consequently incapable of complete and healthful assimilation, and, far from acting as constructive material for tissue regeneration, proves an added systemic burden and a source of toxication. Another cause of loss of weight, slighter in degree, is discovered in that brain and nerve tissue, as instruments for the expression of thought, motion, and sensation, are protected from deterioration in substance by that provision of nature which permits them to utilize nourishment stored in the interstices of tissue. This they consume in illness and in health, and, when in disease normal balance is disturbed, when body tissue is not rebuilt as is the case in health, nerve substance is still supported from the same source of supply.

With slight differences the physiology of digestion in all mammals is markedly similar. In disease the lower mammalia abstain from food until hunger returns, when health is rapidly recovered. To this they are impelled by instinct, by animal sagacity, a faculty implanted by nature in the whole of animate creation. The fasts which animals instinctively undergo in disease are phenomena which cannot help but be constantly observed, but which are not in general intelligently perceived. A common expression in reference to illness in the horse embodies the phrase, "off his feed," and this negation on the part of the animal confirms the existence an instinctive sense that impels it to fast when its physical well-being is overturned. And this natural spontaneous impulse is not confined to mammals, for birds, reptiles, in fact the whole animal kingdom, abstain from food when ailing. A python in captivity has been known to fast for thirteen months, with great loss in weight, it is true, but with eventual recuperation and recovery. And cats and canines often prolong abstention to skeleton condition, after which strength and vitality progressively increase until normal is again attained. Instances such as these may be multiplied indefinitely.

While not occasioned by the invasion of disease, it is interesting to note in this connection that condition of lethargy undergone by certain animals during the winter months, known as hibernation, a condition in which the functions of the body are in great measure suspended. How a warm-blooded animal used to the most stirring activities during eight or nine months of the year can retire to a den, and from an ordinary sleep, which it is at first, pass into a condition of torpor in which all the organs that have to do with digestion, assimilation, and waste, excepting the lungs, suspend their functions and remain quiescent for a period of several months, is more or less a sealed book to science.

In man and the non-hibernating animals the action of the body functions are continuous awake or asleep, but in the bear, the marmot, the prairie dog, during the hibernating period, the functions of digestion, assimilation, and elimination are suspended until the animal awakens in the spring.

A bear, if sufficiently fat, begins to fast some weeks before he retires to winter quarters; but, if there has been lack of food, or, if the animal is old, with poor teeth, it will eat to the very day of entering its den, and this last meal will be found in the stomach when the revival from winter sleep takes place.

The average bear at the beginning of hibernation is covered with a layer of fat that varies from two to six inches in thickness, and, if the animal is killed at this time and the fat removed from the carcass, the latter is found plump and full-fleshed. But, killed after some months in the den, a heavier layer of fat is discovered, with a diminution in lean flesh, which by this time has become lax and flabby in texture. The carcass, then stripped of its fat, will be noticeably smaller than that of a bear of similar size killed in the fall or in the early winter.

There is then evidently a continual process of change from nitrogenous to carbonaceous tissue proceeding while the winter sleep of the hibernating animal endures; and, in this transmutation of muscle into fat, lies perhaps the secret of the torpor in which the bear is wrapped. For, when a bear first goes into his den, his sleep is natural, and he is easily aroused. But, left undisturbed, sleep develops into stupor; respiration and circulation are the only evidences of life, and they are both retarded in action. Carbon resulting from the change of protein into fat within the system, is retained in the blood, because all of the organs of elimination, excepting the lungs, are without function; and respiration is so slow that there is continuously an excess of carbonic acid gas in the blood stream, and a consequent condition of toxication, of torpor.

At times during hibernation the female bear will bring her young into the world, and then milk is elaborated in amount sufficient to maintain the cubs. The birth of young and the physiological chemistry of continued milk production in the fasting, torpor-ridden bear have particular interest here, analogous as these phenomena are to the related cases in the text of pregnant women proceeding to confinement, but fasting for weeks the while.