ALIMENTARY TRACT AS AN EXCRETORY SYSTEM. 317 



pected to be of the utmost practical value in medicine. It 

 was shown above to how great an extent certain inorganic 

 substances are eliminated by the alimentary tract. FLEXNER 

 has found that the toxin of the SHIGA bacillus, no matter 

 how introduced into the body, is eliminated through the 

 intestinal tract, and in this elimination gives rise to the 

 ulcers found in the dysentery produced by this organism. 

 The recognition of the fact that morphin is secreted into 

 the stomach, even when subcutaneously introduced, has led 

 to the practice of gastric lavage for morphin poisoning; and the 

 knowledge that arsenic appears in the gastro-intestinal tract, 

 no matter how it is given, has led to scientific methods of 

 recognizing cases of poisoning by this element, not only for 

 diagnostic but also for medico-legal purposes. 



2. The Character of the Alimentary Contents. The Faeces. 

 The alimentary contents differ markedly in general appear- 

 ance and chemical composition in the various portions of the 

 alimentary tract. The reasons for this are readily ap- 

 parent. Not only does the food of different animals differ, 

 but it is not always the same in the same animal. In its 

 passage from the mouth to the anus it is acted upon by the 

 various portions of the canal through which it passes, and 

 changes are wrought in it of a mechanical and chemical char- 

 acter. Not only is its physical state of aggregation pro- 

 gressively altered in this way, but it has poured out upon it, 

 one after the other, a number of secretions, each of which, by 

 virtue of the substances contained in it ; alters the chemical 

 composition of the alimentary contents. The metabolic 

 products excreted by the bacteria accomplish a similar end. 

 To the changes brought about in this way must be added 

 those induced through the absorption from the alimentary 

 contents of certain of the substances contained in them. 

 All these are together responsible for the progressive change 

 which the food suffers in its passage from the mouth to the 

 anus. 



The food enters the mouth in a state of coarse division, 



