Page:Popular Science Monthly Volume 35.djvu/825

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digestion of mammals can be summed up in the simple way now prevalent seems to us too broad an assumption. The field is very wide, and as yet but little explored.

Human Physiology.—The study of Alexis St. Martin has furnished probably the best example of genuine human physiology to be found, and has yielded a harvest rich in results.

We suggest to the student that self-observation, without interfering with the natural processes, may lead to valuable knowledge; for, though it may lack some of the precision of laboratory experiments, it will prove in many respects more instructive, suggestive, and impressive, and have a bearing on medical practice that will make it telling. Not that we would be understood now or at any time as depreciating laboratory experiments, but we wish to point out from time to time how much may be learned in ways that are simple, inexpensive, and consume but little time.

The law of rhythm is illustrated, both in health and disease, in striking ways in the digestive tract. An individual long accustomed to eat at a certain hour of the day will experience at that time not only hunger, but other sensations, probably referable to secretion of a certain quantity of the digestive juices and to the movements that usually accompany the presence of food in the alimentary tract. Some persons find their digestion disordered by a change in the hours of meals.

It is well known that defecation at periods fixed, even within a few minutes, has become an established habit with hosts of people; and the same is to a degree true of dogs, etc., kept in confinement, taught cleanly habits, and encouraged therein by regular attention to their needs.

Now and then a case of what is very similar to regurgitation of food in ruminants is to be found among human beings. This is traceable to habit, which is bound up with the law of rhythm or periodic increased and diminished activity.

Indeed, every one sufficiently observant may notice in himself instances of the application of this law in the economy of his own digestive organs.

This tendency is important in preserving energy for higher ends, for such is the result of the operation of this law everywhere.

The law of correlation, or mutual dependence, is well illustrated in the series of organs composing the alimentary tract.

The condition of the stomach has its counterpart in the rest of the tract: thus, when St. Martin had a disordered stomach, the epithelium of his tongue showed corresponding changes.

We have already referred to the fact that one part may do extra work to make up for the deficiencies of another.

It is confidently asserted of late that, in the case of persons