

SURVEY OF DIGESTION AS A WHOLE 421 



stantly going on. It has been actually shown that small particles, 

 such as lycopodium spores, suspended in water, soon reach the 

 stomach when injected into the rectum. So that micro-organisms, 

 aided by the antiperistalsis of the colon, may be able to work their 

 way above the ileo-colic sphincter and valve, even against the 

 downward peristaltic movement of the small intestine. But even if 

 this were not the case, a few bacteria or their spores, passing through 

 the stomach with the food, would be enough to set up extensive 

 changes as soon as they reached a part of the alimentary canal 

 where the conditions were favourable to their development. In- 

 deed, from the time when the first micro-organism enters the diges- 

 tive tube soon after birth, it is never free from bacteria; and their 

 multiplication in one part of it rather than another depends not so 

 much on the number originally present to start the process, as on 

 the conditions which encourage or restrain their increase. 



A certain amount of already emulsified fats is broken up into 

 their fatty acids and glycerin in the stomach, unemulsified fats 

 entirely by the fat-splitting ferment of the pancreatic juice. The 

 acids will form soaps with alkalies wherever they meet them in the 

 intestinal contents, or even in the mucous membrane. A portion 

 of those soluble soaps may be immediately absorbed; the rest will 

 aid in the emulsification of the fats not yet chemically decomposed, 

 and thus greatly hasten the fat -splitting action of the pancreatic 

 juice. The phosphatides are in all probability acted upon in the 

 alimentary canal much in the same way as the fats. Lecithin is 

 decomposed by pancreatic and intestinal juice into fatty acids and 

 glyceryl-phosphoric acid, and cholin is liberated. As regards the 

 behaviour of the sterins of the food little is known, but it is not 

 unlikely that their esters are split up, and the sterins thus set free 

 as well as those originally free in the food may then be absorbed, 

 in part at least, without further change. The starch and dextrin 

 which have escaped the action of the saliva are changed into 

 maltose by the amylase of the pancreatic juice, and the maltose 

 into dextrose by the maltase of the same secretion and of the succus 

 entericus. 



The succus entericus, in addition to its important functions 

 already mentioned, aids as an alkaline liquid in lessening the acidity 

 of the chyme and establishing the reaction favourable to intestinal 

 digestion. It will convert into monosaccharides any cane-sugar, 

 maltose, or lactose, which may reach the intestine; but it cannot 

 be doubted that some cane-sugar may be absorbed by the stomach, 

 after being inverted by the hydrochloric acid of the gastric juice 

 or by inverting ferments taken in with the food, or on its way 

 through the gastric walls. 



Upon the whole no great amount oi water is absorbed in the small 

 intestine, or at least the loss is balanced by the gain, for the intestinal 



