DIGESTION AND RELATED FUNCTIONS. 799 



digestion of mammals can be summed up in the simple way now 

 prevalent seems to us too broad an assumption. The iield 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 physi- 

 ology to be found, and has yielded a harvest rich in results. 



We suggest to the student that self -observation, without in- 

 terfering with the natural processes, may lead to valuable knowl- 

 edge ; for, though it may lack some of the precision of laboratory 

 experiments, it will prove in many respects more instructive, sug- 

 gestive, 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 accus- 

 tomed 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 every- 

 where. 



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 



