THE LIVER AND BILE 763 



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 con- 

 tact 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 mem- 

 brane 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 excre- 

 tion 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 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 spontaneous activity of the liver cells or have 

 arrived at them after absorption from the alimentary canal. Such questions 

 can be decided only 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 

 a 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. 



