DIGESTION 395 



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 invert 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 of water is absorbed in the 

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

 the intestinal contents are as concentrated in the duodenum as 

 in the ileum. But as soon as they pass beyond the ileo-csecal 

 valve water is rapidly absorbed, and the contents thicken into 

 normal faeces, to which the chief contribution of the large intestine 

 is mucin, secreted by the vast number of goblet cells in its 

 Lieberkiihn's crypts. 



Bacterial Digestion. So far we have paid no special atten- 

 tion to other than the soluble ferments of the digestive tract, 

 although we have incidentally mentioned the action of the lactic 

 acid bacilli on carbo-hydrates and of the fat-splitting bacteria 

 on fats. It is now necessary to recognise that the presence of 

 bacteria is an absolutely constant feature of digestion ; and 

 although their action must in part be looked upon as a necessary 

 evil which the organism has to endure, and against the conse- 

 quences of which it has to struggle, it is not unlikely that in 

 part it may be ancillary to the processes of aseptic digestion. 

 But bacteria are not essential (in mammals, at any rate, living 

 on milk), as some have supposed. For it has been shown 

 that a young guinea-pig, taken by Caesarean section from its 

 mother's uterus with elaborate aseptic precautions, and fed in an 

 aseptic space on sterile milk, grew apparently as fast as one of 

 its sisters brought up in the orthodox microbic way. The 

 alimentary canal remained free from bacteria (Nuttall and 

 Thierfelder) . On the other hand, chickens hatched from sterile 

 eggs and kept in a sterile enclosure lived, indeed, for a time, 

 but did not thrive in comparison with the control animals, and 

 died at latest after eighteen days (Schottelius). It is probable 

 that the difference in the results is to be attributed to the 

 difference in the food, purely vegetable food requiring the aid of 

 bacteria for its proper digestion, while an easily-digestible food 

 like milk does not. 



Among the more important actions of bacteria on the protein 

 food-products in the intestines may be mentioned the formation 

 of indol, phenol, and skatol, the first having tyrosin for its pre- 

 cursor, and being itself after absorption the precursor of the 



