332 VETERINARY PHYSIOLOGY 



circulation. Among these substances are the salts of the 

 bile acids and their derivatives, many alkaloids such as 

 curarine, and in all probability the amines formed by 

 putrefactive decomposition of proteins in the gut. The 

 liver thus forms a protective barrier to the ingress of certain 

 poisons. 



2. Enzymes — Ptyalin appears to be destroyed in the 

 stomach by the hydrochloric acid. Pepsin is probably 

 partly destroyed in the intestine, but a proteolytic enzyme 

 acting in an acid medium is present in the urine, and this 

 may be absorbed pepsin. Trypsin appears to be destroyed 

 in the alimentary canal ; but the fate of the other pancreatic 

 enzymes and of the enzymes of the succus entericus is 

 unknown. 



3. Bile Constituents- — 1. The bile salts are partly re- 

 absorbed from special parts of the small intestine — sodium 

 glycocholate being taken up in the jejunum and taurocholate 

 in the ileum. The acids of these salts are also partly broken 

 up. The glycocholic acid yields amino-acetic acid, which 

 is absorbed and passes to the liver to be excreted as urea ; 

 while the taurocholic acid yields amino-isethionic acid, which 

 goes to the liver, and yields urea and probably sulphuric 

 acid. The fate of the cholalic acid is not known, but it is 

 supposed to be excreted in the faeces. 2. The 'pigments 

 undergo a change and lose their power of giving Gmelin's 

 reaction. They appear in the faeces as stercobilin. It is 

 probably formed by reduction of bilirubin in the intestines 

 as the result of the action of micro-organisms. 3. The 

 cholesterol is passed out in the faeces in a modified form as 

 co23rosterol. 



F. Movements of the Intestine. 

 1. The Small Intestine. 



These are of two kinds — segmental and peristaltic. 



1. The segmental movements consist in the formation of 

 local constrictions, which divide the gut up into little 

 segments or compartments. A constriction next forms in 

 the middle of each of these, and the former constriction is 



