344 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



ligation of the former. This seems to indicate that oxidation 

 plays an important part in the formation of urea in the liver 

 (Doyon and Dufourt)." 



That the substances thus oxidized reach the liver by the 

 portal vein needs hardly to be emphasized. But Foster says: 

 "The introduction of even a small quantity of proteid mate- 

 rial into the alimentary canal at once increases the urea in the 

 urine, and in the curve of the discharge of urea in the twenty- 

 four hours each meal is followed by a conspicuous rise. . . . 

 We have seen reason to think that the proteids of a meal are 

 absorbed not by the lacteals, but by the portal blood-vessels, 

 and such bodies as leucin probably take the same course. This 

 being so, all these bodies pass through the liver and are sub- 

 jected to such influences as may be exerted by the hepatic 

 cells." 



Such bodies of leucin one of the main products of nitrog- 

 enous dissociation naturally follow the same course. Drech- 

 sel has suggested that all bodies of this class i.e., leucin, 

 tyrosin, glycocoll, etc. first undergo oxidation in the tissues, 

 and that their ammonia and carbonic acid then combine syn- 

 thetically, forming ammonium carbamate, this, in turn, being 

 carried to the liver and there transformed into urea. 



It is clear that these ammonia compounds take the course 

 outlined by Foster: i.e., the venules of the villi, the mesenteric 

 veins, and finally the portal vein. That they undergo oxida- 

 tion in the blood of these vessels, however, is not likely, for 

 they contain probably the most watery blood of the organism, 

 and that most depleted of its oxygen. 



Quite another field of activity is afforded, however, when 

 the hepatic lobule is reached; here the ammonia compounds 

 meet the oxidizing substance brought ~by the hepatic artery's capil- 

 laries. Taking the ammonium compound referred to by Drech- 

 sel for example, the series of reactions outlined by him seem 

 to follow in normal sequence: 1. In the portal vein: hydro- 

 lytic cleavage with the formation of amido-bodies, such as 

 leucin, tyrosin, aspartic acid, glycocoll, etc. 2. In the hepatic- 

 lobule capillaries and their oxidizing substance: oxidation, 

 with the formation of ammonia, carbonic acid, and water, fol- 

 lowed by the synthetic union of ammonia and carbonic acid, 



