502 A MANUAL OF PHYSIOLOGY 



takes place in the liver. Further, the blood of the portal vein 

 during digestion contains several times as much ammonia as the 

 arterial blood, and the excess disappears in the liver. 



(3) Uric acid which in birds is the chief end-product of 

 protein metabolism, as urea is in mammals is formed in the 

 goose largely, and almost exclusively, in the liver. This has 

 been most clearly shown by the experiments of Minkowski, who 

 took advantage of the communication between the portal and 

 renal-portal veins (p. 356) to extirpate the liver in geese. When 

 the portal is ligatured the blood from the alimentary canal can 

 still pass by the roundabout road of the kidney to the inferior 

 cava, and the animals survive for six to twenty hours. While 

 in the normal goose 50 to 60 per cent, of the total nitrogen is 

 eliminated as uric acid in the urine, and only 9 to 18 per cent, 

 as ammonia, in the operated goose uric acid represents only 

 3 to 6 per cent, of the total nitrogen, and ammonia 50 to 60 per 

 cent. A quantity of lactic acid equivalent to the ammonia 

 appears in the urine of the operated animal, none at all in the 

 urine of the normal bird. The small amount of urea in the 

 normal urine of the goose is not affected by extirpation of the 

 liver. And while urea, when injected into the blood, is in the 

 normal goose excreted as uric acid, it is in the animal that has 

 lost its liver eliminated in the urine unchanged. 



(4) After removal of the liver in frogs, or in dogs which have 

 survived the previous connection of the portal vein with the 

 inferior vena cava by an Eck's fistula (p. 356), the quantity of 

 urea excreted is markedly diminished, and the ammonium salts 

 in the urine are increased. When the Eck's fistula is established 

 and the portal vein tied, without any further interference with 

 the hepatic circulation, the amount of urea in the urine is not 

 lessened to nearly the same extent, evidently because the sub- 

 stances from which urea is formed still, for the most part, gain 

 access to the liver through the hepatic artery and by means of 

 the back-flow which is known to take place through the hepatic 

 vein. Yet while in normal dogs the proportion of ammonia to 

 urea in the urine is only i : 22 to i : 73, in dogs with Eck's 

 fistula it rises to i : 8 to i : 33. If the animals are kept on a 

 diet poor in proteins, no symptoms may develop for a considerable 

 time. But if much protein is given, characteristic symptoms, 

 including convulsions, always appear. These may be produced 

 by the saturation of the organism with ammonia compounds, 

 which are formed from the proteins as in the normal animal, 

 but which the liver, with its circulation crippled, is unable to 

 cope with, and to completely change into urea, although the 

 statement has been made that when ammonia or ammonium 

 salts are injected into the blood larger quantities must be present 



