ACTION OF MICRO-ORGANISMS IN THE INTESTINES 391 



partly dissolved in the stomach are subjected chiefly to the action of the 

 pancreatic juice. The pepsin is rendered inert by the bile. The pancreatic 

 trypsin proceeds with the further conversion of the proteoses into peptones, 

 and, with the erepsin, of the peptones into leucin, tyrosin, and the other 

 amino-acids. (3) The starchy portions of the food are now acted on briskly 

 by the pancreatic juice and the succus entericus, and are changed to maltose 

 and dextrose. (4) Salines are usually in a state of solution before they 

 reach the intestine. 



Digestive Changes in the Large Intestine. The changes which take 

 place in the chyme in the large intestine are probably only the continuation 

 of the same changes that occur in the course of the food's passage through 

 the upper part of the intestinal canal. No special enzymes have been clearly 

 shown for the mucous membrane of the large intestine. The enzymes of the 

 small intestine may continue their action here, being hindered only by the 

 acid developed from fermentation processes. 



Action of Micro-organisms in the Intestines. Certain changes take 

 place in the intestinal contents independent of, or at any rate supplemental 

 to, the action of the digestive ferments. These changes are brought about 



0. 



O 

 " O 



C 



I 



f 



FIG. 276. Types of Micro-organisms, a, Micrococci arranged singly; in twos, 

 diplococci if all the micrococci at a were grouped together, they would be called staphylo- 

 cocci and in fours, sarcinae; b, micrococci in chains, streptococci; c, and d, bacilli of 

 various kinds, one is represented with flagellum; e, various forms of spirilla;/, spores, either 

 free or in bacilli. 



by the action of micro-organisms or bacteria. We have indicated elsewhere 

 that the digestive ferments are examples of unorganized ferments, so bacteria 

 are examples of organized ferments. Organized ferments, of which the yeast 

 plant may be taken as a typical example, consist of unicellular vegetable organ- 

 isms, which when introduced into a suitable medium grow with remarkable 

 rapidity. By their growth they produce new substances from those supplied to 

 them as food. Thus, for example, when the yeast cell is introduced intou solu- 

 tion of grape-sugar, it grows, and alcohol and carbon dioxide are produced. 

 The alcohol and carbon dioxide arise from the formation by the cell of some 

 chemical substances which are allied to the unorganized ferments and which 

 greatly increase in amount with the multiplication of the original cell. In 



