FOOD AND DIGESTION. 401 



the alimentary matters or iu the digestive fluids, or both. The acid 

 reaction, which had disappeared in the small bowel, again becomes very 

 manifest in the caecum probably from acid fermentation processes in 

 some of the materials of the food. 



There seems no reason to conclude that any special secondary diges- 

 tive process occurs in the caecum or in any other part of the large in- 

 testine. Probably any constituent of the food which has escaped 

 digestion and absorption in the small bowel may be digested in the large 

 intestine; and the power of this part of the intestinal canal to absorb 

 fatty, albuminous, or other matters, may be gathered from the good 

 effects of nutrient enemata, so frequently given when from any cause 

 there is difficulty in introducing food into the stomach. In ordinary 

 healthy digestion, however, the changes which ensue in the chyme after 

 its passage into the large intestine are mainly the absorption of the 

 more liquid parts; the chief function of the large intestine being to act 

 as a reservoir for the residues of digestion before their expulsion from 

 the body. 



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 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, torula 



0, 



f , * 



' s 



Fig. 274. Types ot micro-organisms, a, micrococci arranged singly; in twos, diplococci if all 

 the micrococci at a were grouped together, they would be called staphylococci and in fours, sar- 

 cinse; 6, micrococci, in chains streptococci ; cand d, bacilli of various kinds, one is represented 

 with flagellum; e, various forms of spirilla; /, spores, either free or in bacilli. 



(saccharomyces} cerevisice, may be taken as a typical example, consist of 

 unicellular vegetable organisms, which when introduced into a suitable 

 culture medium grow with remarkable rapidity, and by their growth 

 produce new substances from those supplied to them as food. Thus for 

 example, when the yeast cell is introduced into a solution of grape sugar, 

 26 



