THE LIVER AND BILE 717 



promoting the closer approach of the lipase of the pancreatic juice to the fats 

 on which it is to act, but it has also the power of dissolving fatty acids and 

 soaps, including even the insoluble calcium and magnesium soaps. It is 

 probable that it aids also in holding in solution, and bringing in contact 

 with the fat, the lipase of the pancreatic juice. It has been shown by 

 Nicloux that the lipase contained in oily seeds, such as those of the castor 

 plant, is insoluble in water, but soluble in fatty media. The dried ferment 

 obtained from the pancreas in many cases yields no lipase to water, but gives 

 a strongly lipolytic solution when extracted with glycerin. The digestive 

 function of bile therefore lies in its power of serving as a vehicle for the 

 suspension and solution of the interacting fats, fatty acids, and fat- 

 splitting ferment. This vehicular function plays an important part 

 in the absorption of fats. These pass through the striated basilar 

 membrane bounding the intestinal side of the epithelium, not, as was 

 formerly thought, in a fine state of suspension (an emulsion), but dissolved 

 in the bile in the form of fatty acids or soaps and glycerin. On the arrival 

 of these products of digestion in the epithelial cells, a process of resynthesis 

 is set up. Droplets of neutral fat make their appearance in the cells, 

 whence they are passed gradually into the central lacteal of the 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 cholagogues with 

 which we are acquainted . By this circulation of bile between liver and intes- 

 tine 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 fseces 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 spontaneous 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. 



