132 THE HUMAN MECHANISM 



The chief seat of the putrefactive decomposition of pro- 

 teins is in the large intestine, where conditions are favorable 

 for the activity of the special bacteria responsible for this 

 food change. The reader will recall the provisions for com- 

 pleting the digestion of proteins and carbohydrates in the 

 small intestine, and these certainly play a very important 

 role in limiting harmful microbic action in the large intestine. 

 It often happens, especially in middle life, that the quantity 

 of food eaten, and of protein food in particular, must be con- 

 siderably diminished to insure complete digestion of these 

 nutrients in the small intestine and thus deprive the putre- 

 factive bacteria of the large intestine of the material out of 

 which to make deleterious substances. 



We have thus far been dealing only with those microbes 

 commonly found in the intestine. At times foreign microbes 

 find entrance, some of which cause such diseases as typhoid 

 fever, dysentery, cholera, etc. The action of these occasional 

 intruders will be more fully dealt with in Part II. 



36. The elimination of intestinal waste. Those who are 

 " blessed with a good digestion " sometimes find it hard to 

 realize that the preparation of food for absorption through the 

 delicate membranes lining the alimentary canal is a difficult 

 and complex process, requiring much delicate physical and 

 physiological apparatus and involving various and important 

 chemical reactions. Even when they realize this, they rarely 

 appreciate the indispensable cooperation and fine adjustment 

 of the several parts and processes concerned. It is just here, 

 however, that a clear understanding is important, for without 

 this it is not easy to see how disorders of digestion arise. 



Let us then remember that the efficient handling of the food 

 in the stomach is aided by the preparatory crushing it receives 

 in the process of mastication ; that in the stomach an adequate 

 and efficient secretion of gastric juice must take place, and that 

 this begins as the result of nervous events connected with 

 our enjoyment of the food when eaten ; that the continued 



