ITS FORMATION. 87 



formed biliary substances. On these grounds, it is necessary that 

 a stringent comparison should be instituted between the blood of 

 the veins which enter and leave the liver. 



In passing to the consideration of the individual biliary sub- 

 stances, and inquiring which of these exist pre-formed in the 

 blood of the portal vein, we find that none of the most essential 

 constituents of the bile can be detected in it The presence of 

 resinous biliary acids, and therefore chiefly of cholic or choloidic 

 acid, in the portal vein, has been conjectured even by those who 

 do not believe in the formation of these acids in other parts than 

 the liver; nor was their presence here to be wondered at, since 

 there appeared to be grounds for assuming that a portion of the 

 bile effused into the intestinal canal was resorbed by the veins, 

 and that the rudiments of this resorbed bile must then of necessity 

 be again collected in the portal vein; yet the most carefully 

 conducted inquiries, instituted under various conditions, have 

 hitherto failed to demonstrate the existence of these resinous 

 biliary acids in the blood of the portal vein. The error of sup- 

 posing that biliary substances have been demonstrated in the 

 blood of the portal vein by means of sugar and sulphuric acid, 

 arises from the similar reaction which Pettenkofer's test gives 

 with olein and oleic acid. 



We endeavoured in the first volume of the present work (see 

 pp. 126 and 2?0) to demonstrate the chemical grounds on which 

 we based our hypothesis that cholic acid must be regarded as a 

 conjugated acid, consisting of a non-isolable modification of oleic 

 acid and a carbo-hydrate. We were led to adopt this view mainly 

 in consequence of the large quantity of olein contained in the 

 blood of the portal vein, in which respect it differs so greatly from 

 the blood of every other vein, including even the hepatic veins. 

 A careful examination of the blood of the portal vein, and a com- 

 parison of this blood with that of the hepatic and other veins, 

 lead almost involuntarily to the conclusion that the oleaginous 

 fats which occur in preponderating quantity in the blood of the 

 portal vein, and are only contained in very small quantity in the 

 blood of the hepatic veins, must participate to a considerable 

 extent in the formation of the bile ; for the blood is rich in olein 

 when it enters the liver, but exhibits only a very small portion 

 when it leaves that organ; the fat of the blood of the hepatic 

 veins is also more consistent, and contains relatively more mar- 

 garin. On an average, the solid residue of the portal blood 



