The portion of the anatomy that we now approach varies in construction almost as much through the animal kingdom as do the external shape and covering of the various orders and much more than do the other systems. The reason for this is obvious, an arrangement accommodative to the differing food chiefly, but not a little to the ease with which animals obtain and assimilate their nutriment. It would be impracticable to describe all the variations of the orders discussed in this study, but since certain gross and minute differences are of importance in comparative pathology they will be discussed at the appropriate places. It is my purpose to present in a subsequent section a discussion of food in captivity from the standpoint of its quality and quantity in relation to pathology. Doubtless the quality of food is the largest factor in the production of disease both of the alimentary tract and elsewhere, but I am not at all sure that the quantity may not be equally important, in certain groups at least. Thus, for example, the ungulate has nearly always available in bedding a substance that he can and will eat, and the prevalent idea that an animal will eat only as much as is good for him seems not to hold at all times, since overfilled rumens are only too common. It might be thought, however, that captivity creates a sort of pica, or that enforced idleness is conducive to gorging. The use a few lines above of the word “doubtless” may have arrested the attention of some, yet when the whole subject is reviewed it seems entirely justified. Plimmer puts incorrect food at the head of the list of the causes of enteritis, Brooks emphasizes the importance of certain grasses and musty fodder, systematic writers detail among the principal causes of gastritis spoiled food, and in zoological gardens specific disease like hog cholera and enterohepatitis are relatively uncommon while nonspecific gastroenteritis is the most frequent diagnosis in causes of death. The other factors to which enteritis is ascribed are animal and vegetable parasites and mechanically operative foreign bodies, the last being unimportant. Just how important the first mentioned are is a matter of some question which must be subjected to considerable study before any solution can be expected.