372 THE FINAL DECOMPOSITION OF FOODSTUFFS IN THE BODY 



been excreted as urea. Now if it be true that only the liver can transform 

 ammonia into urea, it follows that only a part of the nitrogen contained in 

 proteid passes over into ammonia,, while another part runs through other 

 stages until finally it also is given off from the body as urea. 



Under normal circumstances ammonia in certain quantities is always present 

 in the urine. This ammonia is necessary in order to help saturate the acids 

 excreted in the urine, for the fixed bases are not sufficient for this purpose. If 

 the acid production in the body is large, or if free acids are taken into the body, 

 the quantity of ammonia is larger and the quantity of urea correspondingly 

 decreases. With increased supply of fixed alkalies the quantity of ammonia falls, 

 and the quantity of urea rises. The formation of urea from ammonia varies 

 therefore according as a greater or less amount of ammonia finds employment 

 as such. It appears to follow from what has already been said that the regula- 

 tion of this function is committed to the liver. 



The uric acid which is eliminated from mammals in general does not 

 represent a product of proteid decomposition, but appears to come mainly 

 from the nucleins (Horbaczewski). The nucleins are split up in the body 

 into proteid, phosphoric acid and purin bases (cf. page 76). The latter 

 pass by oxidation over into uric acid ; however, some purin bases besides uric 

 acid occur in the urine, though the quantity of these is rather small. 



Eecent observations (Burian and Schur, Siven) have proved that uric acid 

 is derived in part from purin bases which are introduced into the body with 

 the food (exogenous), and in part from those present in the body itself 

 (endogenous). 



The amount of the latter is constant for the same individual for an adult 

 man in health amounting to 0.3-0.6 g. (=0.1-0.2 g. 1ST) per day. It can be 

 determined directly if a diet containing no nucleins (purin bases) consisting 

 for example of milk, cheese, eggs, potatoes, rice, white bread, etc. be given. 

 The amount of purin bases and of uric acid in the urine is then relatively con- 

 stant, notwithstanding that very great variations in the quantity of proteid 

 may be supplied in such foods. We have no positive information yet as to the 

 processes upon which the so-called endogenous acid depends. 



If, however, the diet consist of foods which contain purin bases (meat, liver, 

 thymus, etc.) the quantity of uric acid eliminated increases in proportion to the 

 amount of purin eaten. The amount of any purin base that will appear in the 

 urine as such, or as the closely related uric acid, depends upon its chemical 

 nature. Thus with hypoxanthin (meat, liver, spleen) one-half, and with adenin 

 (thymus) one-fourth of the purin nitrogen fed appears again in essentially the 

 same form in the urine (Burian and Schur). 



According to the investigations of Wieners, uric acid is formed at least in 

 the liver, the thymus and spleen, and it is not unlikely that all the organs par- 

 ticipate in its production according to the quantity of nucleins contained in them. 



At any rate, the purin derivatives given off in the urine of mammals is only 

 a fractional part of that taken up in the food, or of that formed in the body 

 itself. A considerable part of both must be further oxidized and be transformed 

 into urea. Probably the best proof of this is the fact that after extirpation of 

 the kidneys, uric acid does not accumulate in the blood. Hence the normal 

 elimination of uric acid might be due to the circumstance that the transforma- 

 tion of urea is not quite complete, but the blood takes the opportunity presented 



