362 ANIMAL PHYSIOLOGY. 
the surface, for one asks the reason of this, if it be a fact, as it 
no doubt is. When we look further into the peculiarities of 
digestion, etc., we recognize the influence of race as such, and 
in the race and the individual that obtrusive though ill-under- 
stood fact—the force of habit, operative here as elsewhere. 
And there can be little doubt that the habits of a people, as to 
food eaten and digestive peculiarities established, become or- 
ganized, fixed, and transmitted to posterity. 
It is probably in this way that, in the course of the evolu- 
tion of the various groups of animals, they have come to vary 
so much in their choice of diet and in their digestive processes, 
did we but know them thoroughly as they are; for to assume 
that even the digestion of mammals can be summed up in the 
simple way now prevalent seems to us too broad an assump- 
tion. The field is very wide, and as yet but little explored. 
Human Physiology.—The study of Alexis St. Martin has fur- 
nished 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 pres- 
ence 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, that are taught cleanly habits, and encouraged 
therein by regular attention to their needs. 
Now and then a case of what is very similar to regurgita- 
tion of food in ruminants is to be found among human beings. 
