9 o6 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. 
Xj r ea. — 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 - 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, 3 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), Virchoiu's Archiv, Bde. cxviii. S. 225 ; cxix. S. 193, cxxxviii. Suppl. 
S. 81 ; v. Meister (in cat and dog), Ccntralbl. f. ally. Path. u. path. Anat., Jena, 1891, Bd. ii. 
