iv DIGESTION IN THE INTESTINE 213 



Boiled starch is rapidly converted into maltose. According to 

 Rohmann the glandular crypts of the jejunum secrete a juice that 

 has a more pronounced diastatic action than that from the crypts 

 of the ileum. Owing again to the action of invertin and lactase 

 enzymes peculiar to the succus entericus (though some hold that 

 they exist in minute quantities in pancreatic juice as well), 

 saccharose and lactose are hydrolysed and converted into mono- 

 saccharides, in which form the carbohydrate introduced with the 

 food is constantly present in the blood. Thus the succus entericus 

 completes the metamorphosis of this important group of food- 

 stuffs, the conversion of which commences in the mouth with the 

 action of the saliva, and is continued with increasing intensity in 

 the duodenum by the action of the pancreatic juice (Paschutin, 

 Eohmann, Bastianelli, Brown and Heron). Lastly the succus 

 entericus, from its alkalinity, co-operates with the bile and the 

 pancreatic juice in neutralising the chyme, in emulsifying the fats, 

 and perhaps also in their cleavage. 



Taken as a whole the results of these experiments in vitro 

 upon the digestive action of the succus entericus secreted by the 

 small intestine bear out the general theory formulated by 

 Hermann to the effect that digestion in the intestine converts the 

 greater part of the solid or colloidal, insoluble and iiidiffusible sub- 

 stances, represented by the protein compounds, the polysaccharides, 

 and the fats, into their respective decomposition or cleavage 

 products or units, which are soluble, readily diffusible, and easily 

 absorbed by the intestinal epithelium, e.g. peptones and amino- 

 acids, glucose, soaps, and free fatty acids. 



II. In order to form a more adequate notion of the sum of the 

 chemical processes which go on in the intestine, it is necessary to 

 examine the changes that take place successively in the acid mass or 

 chyme in the different parts of the gut, owing to the synchronous 

 action of the three secretions whose activity we have been 

 separately considering, in so far as it can be detected from artificial 

 digestions of the natural food-stuffs. 



But there is a preliminary question. In Chapter II. we saw 

 that the secretion of bile from the liver is continuous, unlike the 

 other digestive secretions, which take place only during digestion, 

 and cease entirely, or almost entirely, during abstinence (see pp. 

 134-138, Fig. 51). But while the secretion of bile is continuous, 

 its excretion or output into the duodenum is not continuous, but 

 periodic, and coincides exactly with that period of digestion in 

 which the acid chyme is spurted by rhythmical jets from the 

 stomach to the intestine. It is therefore evident that in the 

 intervals between digestion, the bile secreted by the liver must 

 all collect within the gall-bladder, which is a lateral diverticulum 

 of the excretory bile-ducts, where the bile becomes condensed by 

 absorption of water. What is the mechanism, by which the bile 



P 1 



