DIGESTION. 



127 



agency in the form of certain bacteria which occur normally in health 

 in varying amounts. Strassburger states that 128,000,000 bacteria 

 may be found in a day, chiefly in the large intestine. They are 

 swallowed by the mouth with the food, drinks, and saliva. The 



Fig. 35. Aspect of an Intestinal Loop before and after Section of its 

 'Nerves. (ARMAND MOREAU, from GLEY.) 



A, Normal segment of intestine. B, Same segment several hours after sec- 

 tion of its nerves. The nerves are represented by fine lines. The distension of 

 the intestine is often much greater than indicated in the figure. 



bacteria are one-celled organisms and are produced with marvelous 

 rapidity. From a physiological point of view we are able to classify 

 them into three groups: (1) fermenting, (2) chromogenic, and (3) 

 pathogenic bacteria. However, only the ferment bacteria interest us. 

 Bacteria of different kinds have been noticed at various times 



