DIGESTION IN THE INTESTINE 145 



maltose and isomaltose in much the same way as the ptyalin of 

 saliva splits starch. Starches which escape salivary digestion, or 

 starch and glycogen eaten by carnivora whose saliva contains no 

 ptyalin thus are digested in the intestine. It has been suggested 

 that perhaps amylopsin is really a mixture of two or more 

 enzymes, which are responsible for different phases of the split- 

 ting of starch into the disaccharide maltoses, one enzyme taking 

 the material as far as the dextrin stage, the other converting dex- 

 trins into maltose and isomaltose. The bile seems to have little 

 or no effect upon the activities of amylopsin. The final stage of 

 the digestion of starch is due to an enzyme maltase which splits 

 maltose into glucose. Pancreatic juice of young animals also 

 contains a lactase which splits lactose. This disappears as the 

 animal grows older unless milk. still forms a part of the diet as 

 in man, pigs, and some other animals. Pancreatic juice has 

 been reported to contain a nuclease which acts on nucleic acid, 

 and splits it into its component parts. 



The Bile 



Causes of Flow, Amount. The bile, secreted by the 

 liver into the gall bladder is poured out into the duodenum 

 by way of the bile duct. It is produced continuously by the 

 liver, but its flow from the gall bladder into the duodenum is 

 intermittent. The mechanism by which the secretion of bile into 

 the digestive tract is controlled is little understood. The action 

 of the acid chyme upon the walls of the duodenum seems to be 

 one of the factors concerned. Probably this is due to hormone 

 action. 



The amount of bile secreted by the liver of man in the course 

 of a day has not been determined accurately under normal con- 

 ditions. 550 c.c. per day has been suggested as a possible amount. 

 It may be less than this, but in all probability the amount is 

 greater. Observations on this point have been made in cases of 

 fistulae, but since the bile under these conditions does not enter 

 the intestine, its neutralizing effect on the acid chyme is lost; 

 this would tend to increase the formation of secretin. But bile 



