212 DIGESTION 



DIGESTION IN THE LARGE INTESTINE. The chief function of the 

 large intestine is undoubtedly absorption, especially of water, and as a 

 reservoir for the ever-accumulating chyle. It is likely, however, that the 

 uses of this part of the gut are more numerous than this, its hydrolysis 

 of proteid, for example, being perhaps of consequence. It has long been 

 known that in diseased conditions of the stomach, etc., a person may be 

 kept alive a long time by enemata of, for example, a solution of the whites 

 of eggs in water, and even when introduced in far too small amount to 

 reach the ileum or jejunum. Berlatsky, working in Pawlow's laboratory, 

 finds that the large intestine not only absorbs proteid, but that it digests 

 it. Milk especially, he thinks, may be digested in this part of the intestine, 

 the reaction there being regularly alkaline. Comparatively little research 

 has been done on zymolysis in the colon. 



Bacteria seem to have a part normally in digestive processes in the 

 intestine, although their influence is possibly more helpful in absorption 

 than in digestion proper. In the small intestine the bacteria are relatively 

 few, but within a day after birth multitudes of them have developed in the 

 colon and rectum, and they continue there through life. Their food is the 

 various organic substances found in the feces (see page 252), especially 

 the undigested bits of proteid and carbohydrate food and cellulose. 

 The changes produced in the proteids by the bacteria are those of putre- 

 faction ; the end-products are the (odorous) substances indol, skatol, etc. 

 The sugars and starches are promptly broken up, and cellulose with the 

 liberation of methane (Moore), but in what manner is not well under- 

 stood. 



It is not obvious then what benefit the colonic bacteria are to their 

 host, and it is possible that to be without them would be advantageous'. 

 Indeed, Arloing has shown that mucin and mucus are destructive of all 

 microorganisms, even the most resistant if time enough be given. This 

 then is probably the chief function of the mucus of the alimentary canal 

 (especially abundant in the colon): to destroy the bacteria or some of 

 them, or to lessen their activity. The well-known work of Nuttall and 

 Thierfelder on guinea-pigs has shown that these young animals thrive 

 for eight. days after birth at least with no bacteria in them. Other 

 researchers suppose, however, that this period is too short to be indicative, 

 and that most animals at least do not grow to maturity without aid from 

 the mysterious action of the bacteria in their intestines. Nevertheless, it is- 

 likely that there are many more bacteria in the colon than can be said to be 

 normal. Those which are the most offensive decompose the proteids and 

 produce thereby a large number of substances of an aromatic and almost 

 alkaloid al nature. These are to a greater or less extent absorbed, and 

 probably do harm, in ways little suspected as yet, before they are either 

 decomposed or excreted bodily in the urine. Could the proteid food- 

 fragments in the colon be lessened, much of this baterial growth would 

 be checked. These fragments probably indicate the excessive ingestion 

 of flesh-foods. Work by Fletcher and by Chittenden has shown a prob- 

 able excess in meat-consumption by all but the poorest classes of society. 



