792 URIC ACID. [BOOK 11. 



system do not give rise to an increase of urea in the blood as they 

 do in the intact organism. And again, when the blood of the 

 portal system is diverted from the liver and sent directly into the 

 vena cava ( 309) the ammonia salts of the urine are largely 

 increased with diminution of the urea. 



When the liver is wholly removed mammals succumb within 

 a period too short to allow satisfactory observations to be made ; 

 but birds may be kept alive after the operation for a considerable 

 time ; and when in geese the liver is removed the uric acid 

 (representing in these animals the urea of the mammal) is largely 

 decreased, while the ammonia of the urine is largely increased. 

 After the removal of the liver also, leucin, glycin, and other amides 

 or amido-acids administered by the alimentary canal no longer 

 increase the uric acid of the urine, as they do in the intact 

 animal. In these animals, the synthesis of ammonia compounds 

 into uric acid, which is parallel to the synthesis into urea 

 occurring in the mammal, seems to take place in the liver, and 

 we may infer is in some way or other effected by the hepatic 

 cells. 



As to the exact way in which ammonia either as such or in 

 form of an amide or amido-acid changes into urea we have 

 no certain knowledge. Ammonium carbonate, we know, is readily 

 formed out of urea by simple hydration, and we may imagine 

 that the living organism can carry out the reverse process and 

 dehydrate ammonium carbonate into urea. There is, however, 

 a certain amount of evidence that not ammonium carbonate but 

 ammonium carbamate is the immediate antecedent of urea ; and 

 indeed, out of the body, by electrolysing a solution of ammonium 

 carbamate with alternating currents, a certain amount of urea may 

 be artificially produced. But this is a matter too obscure to be 

 discussed here. 



490. Uric Acid. This, like urea, is a normal constituent of 

 human urine, and, like urea, has been found in the blood, in the 

 liver and in the spleen; it is a conspicuous constituent of an 

 extract of the latter organ. In some animals, such as birds and 

 most reptiles, it takes the place of urea. In various diseases the 

 quantity in the urine is increased ; this is especially the case in 

 leucaemia. At times, as in gout, uric acid accumulates in the 

 blood, and a deposit of urates takes place in the tissues. Since 

 by oxidation a molecule of uric acid can be split up into two 

 molecules of urea, and a molecule of some carbon acid, uric 

 acid is commonly spoken of as a less oxidised product of proteid 

 metabolism than urea. But there is no evidence whatever to 

 shew that the former is a necessary antecedent of the latter; 

 on the contrary, all the facts known go to shew that the ap- 

 pearance of uric acid is the result of a metabolism slightly 

 diverging from that leading to urea; indeed it is probable that 

 the divergence occurs towards the end of the series of changes, for 



