THE BILE 807 



whence they are passed gradually into the central lacteal villus and 

 so into the lymphatics of the mesentery and into the thoracic duct. 

 The bile salts thus released from their function as carriers are absorbed 

 by the blood circulating through the capillaries of the villi, and carried 

 by the portal vein to the liver. On arrival they are once more 

 taken up by the liver-cells and turned out into the bile. Owing to the 

 fact of their ready excretion by the liver- cells, bile salts are the most 

 reliable cholalogues with which we are acquainted. By this circula- 

 tion of bile between liver and intestine the synthetic work of the liver 

 in the production of the bile salts is reduced to a minimum, and 

 it has only to replace such of the bile salts as undergo destruction 

 in the alimentary canal, under the influence of micro-organisms, 

 and are lost to the organism by passing out in the faeces as a gummy 

 amorphous substance, known as dyslysin. Further investigation 

 is still wanted as to the exact method in which secretin acts on the 

 liver-cells, and especially as to whether it actually excites in them 

 the manufacture of fresh bile salts, or whether it simply hastens 

 the excretion of such bile salts as have been formed by the spon- 

 taneous activity of the liver-cells or have arrived at them after 

 absorption from the alimentary canal. Such questions can only 

 be decided by studying the action of secretin on animals possessing a 

 permanent biliary fistula. 



The effect of various diets on the secretion of bile has been studied 

 by Barbera. He finds that, whereas the secretion of bile is greatest 

 on a meat diet, it is somewhat less on a diet of fat, and is insignificant 

 on a purely carbohydrate diet. That is to say, the secretion of bile 

 is greatest on those diets the digestion of which is attended by the 

 passage of a large amount of acid chyme or of oil into the duodenum. 

 Oil is almost as efficacious as acid in promoting the production of 

 secretin in the living duodenum, the production in this case being 

 probably determined by the formation of soap from the oil, and the 

 direct action of the soap on the prosecretin in the epithelial cells of 

 the gut. 



THE INTESTINAL JUICE 



For the development of one of its most important properties, 

 namely, that of proteolysis, the pancreatic juice is dependent on the 

 co-operation of the intestinal juice or succus entericus. Besides this 

 activating power on the pancreatic juice, the intestinal juice has 

 numerous other functions to discharge in the digestion of the food- 

 stuffs. In spite of the great similarity which obtains between the 

 microscopic structure of the wall of the gut at different levels from 

 duodenum to ileocolic valve, functionally there are many differences 

 between the upper, middle, and lower portions of the gut. Speaking 



