3 66 VETEEINAEY PHYSIOLOGY 



can be retained and built into the protoplasm of the animal. 

 Vernon has shown that a similar proteolytic enzyme is widely 

 distributed in the tissues, being specially abundant in the kidney. 

 (4) Enterokinase a zymin which, acting on trypsinogen, con- 

 verts it into active trypsin (p. 364). 



Mechanism of Secretion. The taking of food leads to a flow 

 of intestinal secretion which reaches its maximum in about three 

 hours ; and this flow is much greater from the upper part of 

 the bowel than from the lower. There is some evidence that 

 the injection of secretin calls forth this secretion, and according 

 to some observers, the injection of succus eiitericus into the 

 circulation acts in the same way. 



As regards the action of nerves very little is known. It 

 has been found that, when the intestine is ligatured in three 

 places so as to form two closed sacs, if the nerves to one of 

 these be divided, it becomes filled with a clear fluid closely 

 resembling lymph. The dilatation of the blood vessels may 

 account for this without secretion being implicated. 



C. Bile 



1. Characters and Composition. The bile is the secretion of 

 the liver, and it may be procured for examination (a) From 

 the gall bladder, or (6) from the bile passages by making a 

 fistula into them. Bile which has been in the gall bladder 

 is richer in solids than bile taken directly from the ducts, 

 because water is absorbed by the walls of the bladder and the 

 bile thus becomes concentrated. 



Analyses of gall bladder bile thus give no information as 

 to the composition of the bile when formed. In several cases, 

 where surgeons have produced biliary fistulse, opportunities 

 have occurred of procuring the bile directly from the ducts 

 during life in man. 



Such bile has a somewhat orange-brown colour, and is more 

 or less viscous, but not nearly so viscous as bile taken from 

 the gall bladder. It has a specific gravity of almost 1005, 

 while gall bladder bile has a specific gravity of about 1030. 

 Its reaction is slightly alkaline, and it has a characteristic smell. 



It contains about 2 per cent, of solids, of which more than 

 half are organic. 



