906 METABOLISM. 



undoubtedly is mainly transformed by oxidation into sulphate, for it is 

 found that the sulphates of the urine go hand in hand with the amount 

 of proteid metabolism which is proceeding (see also p. 630). 



Nitrogenous metabolism in the liver. That a very important part 

 of the nitrogenous metabolism of the body occurs in the liver, has been 

 insisted upon, and the experiments which have led to our knowledge on 

 this matter have already been incidentally referred to. 



Urea. The evidence of the formation of urea in the liver was 

 obtained by v. Schroder in a series of researches of remarkable interest 

 and importance. Schroder 1 first determined that this substance was not 

 formed in the kidneys, at least exclusively. He found that when the 

 kidneys were extirpated in a dog, the amount of urea in the blood was 

 increased in the next twenty -four hours to four times the normal 

 quantity (from 0'05 per cent, to 0*2 per cent.). Nor was he able to 

 obtain any increase of urea in blood passed through the kidney, even 

 when such blood contained substances (e.g. carbonate of ammonia) which, 

 by the liver, are capable of being synthetised into urea. This is the 

 more striking, because, as we have seen, the kidneys are capable of 

 performing such an important synthetic process as the formation of 

 hippuric acid from benzoic acid and glycine (Bunge). 



Schroder also showed that urea is not formed in the muscles. 

 He found that blood containing carbonate of ammonia, when perfused 

 through the hind-limbs of a dog, showed no increase of urea. On the 

 other hand, blood similarly treated, and passed several times through 

 the liver of a freshly-killed animal, was found to contain twice or three 

 times the amount of urea which it had before passing through the 

 organ. It was necessary for success in these experiments that the liver 

 should be taken from a well-nourished animal. If removed from a 

 fasting dog no urea was formed. A similar result, obtained by 

 Schondorff, has been already referred to (p. 903). 



These experiments were repeated by Salomon 2 both upon sheep 

 and dogs. They show conclusively that the liver is capable of 

 forming urea from carbonate of ammonia. We have already seen 

 that it is also capable of forming urea from blood containing the 

 products of digestion. Other salts of ammonia besides carbonate 

 are found to be effective; amongst others lactate and carbamate 

 of ammonia, and also the amido-acids, such as leucine and glycine. 

 On the other hand, in extensive disease of the liver, especially 

 of rapid occurrence, and in experiments involving removal of the 

 liver in mammals, combined with the establishment of a communica- 

 tion between the portal and the general venous system, so that 

 there should be no stasis of blood in the capillaries of the intestinal 

 circulation, ammonia salts are found to largely replace urea in the urine, 

 such salts taking the form of lactates and of carbamates (p. 908). With 

 partial extirpation of the liver, 8 and also with phosphorus poisoning, in 

 which the liver cells undergo extensive degeneration, there is also a 

 greater or less diminution of urea in the urine, and a corresponding 

 increase of ammonia; as regeneration occurs, the urea becomes again 

 gradually increased. The same has also been noted in extensive disease 

 of the liver, especially when of rapid occurrence, but also in cases of 



1 See note 2, p. 902. 2 Ibid. 



3 Ponfick (in rabbit), Virchow's Archiv, Bde. cxviii. S. 225 ; cxix. S. 193, cxxxviii. Suppl. 

 S. 81 ; v. Meister (in cat and dog), C'entralbl. f. allg. Path. u. path. Anat., Jena, 1891, Bd. ii. 



