[Il] THE DIGESTIVE ORGANS 47 



whereas its presence in the sheep and ox has been attributed to 

 the fact that these are ruminating animals in which the passage 

 of food into the duodenum only occurs at stated intervals when 

 the presence of bile is desirable, the fluid being stored in the gall 

 bladder between whiles. This explanation, however, is scarcely 

 adequate in view of the facts recorded above that the deer and 

 roe which ruminate have no gall bladder, whereas the pig Avhich 

 does not ruminate possesses one. 



Obstruction of the bile duct, due for example to a flux of 

 mucus leading to its closure, or to disease, causes the bile to pass 

 into the blood, and this produces the disease known as jaundice. 



The Pancreas. The sweetbread or pancreas is a diffuse 

 gland lying in the loop of the duodenum and communicating 

 with it by a duct which usually opens into its ascending portion. 

 In the horse and the sheep there is a common aperture for both 

 bile duct and pancreatic duct but in the ox, pig and dog the 









Fig. '2d. Section of piincieas (after Harris from 

 Halliburton), showing alveoli and i.slets of 

 Langerhans. 



ducts open separately. In structure the pancreas presents a 

 general similarity to the salivary glands, but in addition to the 

 secretory alveoli it contains certain cells which have a different 

 staining reaction and do not communicate with the secretory 

 ducts. These constitute the islets of Langerhans and are referred 

 to again later in describing the pancreas as an organ of internal 

 secretion. The secretory cells contain granules which are 

 probably zymogenic. They disappear after prolonged activity 

 of the gland. 



