174 FUNCTIONS OF NUTRITION. 



is always acid, usually even to its lowest portions. Moreover, some 

 of the products of artificial digestion do not occur with the same readi- 

 ness in the intestine of the living animal. In Kiihne's experiments on 

 the artificial digestion of coagulated fibrine by trypsine solutions, about 

 one-half the peptone produced was further decomposed into other pro- 

 ducts, especially leucine and tyrosine. In the observations of Schmidt- 

 Mulheim, on the contrary, the acid contents of the small intestine in 

 dogs, during the digestion of meat, were very poor in leucine and tyro- 

 sine, but abundant in peptone. He concludes that the digestion of 

 albumen is almost wholly performed by the pepsine ferment in an acid 

 menstruum, that is, by the gastric juice; and that the office of the 

 pancreatic juice in this respect is secondary. 



Bile. 



As compared with other accessory glands of the alimentary canal, 

 the liver presents several striking peculiarities. First, its supply of 

 blood is from two different sources ; namely, the hepatic artery and the 

 portal vein. The ramifications of the hepatic artery are distributed 

 to the walls of the hepatic ducts and of the portal vein, to the capsule 

 of Glisson and to the peritoneal covering of the organ ; while those 

 of the portal vein pass into the glandular parenchyma, and, after 

 traversing its substance as a capillary plexus, become continuous with 

 the rootlets of the hepatic vein. Beside arterial blood, accordingly, 

 which the liver receives in moderate quantity, it is supplied with venous 

 blood in great abundance, conveyed by the portal system from the 

 stomach, the spleen, the pancreas, and the intestine. 



Secondly, the liver is distinguished by its size. While the weight 

 of all the salivary glands together, in man, is but little over 100 

 grammes, and that of the pancreas about 75 grammes, the liver forms 

 a compact vascular and glandular organ, weighing nearly or quite 1600 

 grammes, and occupying a considerable portion of the abdominal 

 cavity. 



Lastly, the liver differs so much in texture from other secretory 

 organs, as to require a special description. The secreting apparatus 

 consists, as usual, of glandular cells and capillary blood-vessels, with 

 ducts for the discharge of the secreted fluid ; but these elements, instead 

 of being arranged as elsewhere in distinct groups of tubules or rounded 

 follicles, are closely united, forming on all sides a continuous mass by 

 mutual contact and adhesion. 



The substance of the liver is divided into masses or islets, about 1.5 

 millimetre in diameter, known as the hepatic lobules. These lobules, 

 however, are not anatomically separate from each other, but are dis- 

 tinguishable only by the arrangement of the afferent and efferent 

 blood-vessels. Each lobule is embraced by the terminal branches of 

 the portal vein, ramifying between the adjacent lobules, and known as 

 the interlobular veins. From the interlobular vein minute vessels 

 into the substance of the lobule, forming by their division and 



