944 THE EXTERNAL SECRETIONS 



vein. These facts clearly show that the secretion of bile is closely 

 dependent upon a proper secretory pressure. It should be noted, 

 however, that the formation of bile takes place in accordance with 

 the same principles as the formation of other secretions; i.e., it is not 

 due to filtration alone but also to osmosis, diffusion, and a certain 

 vital activity on the part of the hepatic cells. To prove this point, 

 it may be shown that these cells are able to secrete against a higher 

 pressure than the portal blood pressure. Thus, if a cannula is inserted 

 in the common duct which in turn is connected with a narrow vertical 

 glass tube, the bile will rise in this tube until its height equals a pres- 

 sure considerably above that prevailing in the portal vein at the hilum 

 of the liver. How rapidly this level will be reached differs with the 

 general condition of the animal. In a robust cat under ether, prob- 

 ably 30 to 60 minutes will be required before the pressure in the com- 

 mon duct will have risen to 15 mm. Hg, which equals twice the pres- 

 sure ordinarily encountered in the portal vein of this animal. In the 

 dog, a pressure of 15 to 20 mm. Hg may be established before the 

 secretion of bile cease's. Clearly, since the hepatic cells are capable 

 of secreting against a pressure higher than that under which they 

 obtain their material, filtration cannot be the only factor concerned 

 in this process. 



A very good proof of the secretory power of the hepatic cells is 

 also furnished by the fact that the constituents of the bile are not brought 

 to the liver in their complete form but are formed here from their 

 precursors. Lastly, it is possible to vary the secretion of bile by chem- 

 ical agents which act in the manner of secretogogues, and stimulate 

 the cells directly. These bile-driving substances are known as chola- 

 gogues. While aloes, calomel, peptone and, salicylates may be used 

 for this purpose, the most powerful agent is the bile itself. Schiff, 

 however, has shown that if the bile is administered by the mouth or 

 through an intestinal fistula, a considerable portion of it is absorbed. 

 Thus, at least a part of the cholagogic action of the constituents of bile 

 may.be due to the fact that the material absorbed is again made use 

 of in the formation of new bile. To prove this point Wertheimer^ 

 injected sheep's bile into the mesenteric vein of a dog and was able to 

 demonstrate the presence of cholohematin in the bile of this animal. 

 This body occurs normally only in the bile of the sheep. 



Icterus. Cholemia. Resorption of Bile. — While it cannot be 

 doubted that the hepatic cells are capable of secreting against a higher 

 pressure than that prevailing in the portal vein, this process cannot 

 be continued indefinitely. The upper limit having been reached, 

 the secretion ceases and some of the constituents of the stagnated 

 bile pass over into the circulation. This resorption gives rise to the 

 condition of icterus or jaundice, which is characterized by a deposition 

 of the biliary pigments in the tissues of the body, causing a yellow 



1 Archive de physiol. norm, et path., 1892, 577; Stadelman, Zeitschr. fiir Biol., 

 xvi, 1897, 1; Whipple and Hooper, Am. Jour, of Physiol., xl, 1916, 349. 



