248 THE URINE. 



These are in part derived from disintegrating cells of the body 

 (endogenous uric acid) and in part from the ingested food (exogenous 

 uric acid). Through the researches of Horbaczewski we know 

 that in the mammalian organism uric acid is formed together 

 with the xanthin bases in all organs of the body, and is most 

 abundantly produced in those which are especially rich in nuclei, 

 such as the spleen and the lymph-glands. Burian further has demon- 

 strated that the muscle tissue also must be viewed as one of the 

 most important sources of uric acid and that hypoxanthin is there 

 its antecedent. The very interesting observation was further made 

 that larger amounts of uric acid could be obtained from these parts 

 when the blood used in the transfusion experiments contained much 

 oxygen, while with venous blood xanthin bases only were obtained. 

 In the amphibia and fish in which the oxidation-processes are especi- 

 ally sluggish, we accordingly find xanthin bases and little or no uric 

 acid. The interesting question now suggests itself, Why is it that 

 in mammals uric acid appears in the urine at all in view of the fact 

 that uric acid which is introduced into the stomach is eliminated as 

 urea ? A final answer to this question cannot be given, but there is 

 reason to suppose that the uric acid is here first carried to the liver, 

 and is probably oxidized to urea by the oxidizing ferments of this 

 organ. We find, as a matter of fact, that an increased elimination 

 of uric acid results at once when the blood of the portal vein is pre- 

 vented from flowing through the liver by establishing a so-called Eck 

 fistula between this and the inferior cava, and when the hepatic artery 

 is at the same time ligated. In this manner the blood of the spleen 

 and the extensive lymphatic districts of the intestinal tract is carried 

 directly into the general circulation, and the contained xanthin bases 

 and uric acid hence find their way into the urine without being sub- 

 jected to the action of the oxydases of the liver. We may hence 

 conclude that the appearance of these bodies in the urine is under 

 normal conditions, owing to the fact that not all the blood of the 

 body reaches the liver before being carried to the kidneys. 



In birds and reptiles we have also seen that a certain amount 

 of urea appears in the urine, and, as I have already explained, this 

 is no doubt produced directly in the tissues. As ingested urea is 

 transformed into uric acid, we must assume that the portion which 

 is eliminated in the urine has reached the kidneys without having 

 previously passed through the liver, and the process is thus quite 

 analogous to what we observe in mammals in the case of uric acid. 



Under normal conditions the elimination of uric acid rarely ex- 

 ceeds 1 gramme, of which 0.3 to 0.6 gramme is represented by the 

 endogenous form. Increased amounts are met with under various 

 pathological conditions. 



In leukaemia especially, a greatly increased elimination is com- 

 monly observed, and referable to the increased destruction of leuco- 

 cytes. But excessive amounts of uric acid may also occur in 

 conditions in which there is no direct evidence of increased nuclear 



