vii KATABOLIC CONSTITUENTS OF UEINE 391 



has the power of breaking up both endogenous and exogenous uric 

 acid, and since the faculty of destroying uric acid manifested by 

 different organs is very considerable, a fraction of the uric acid 

 which circulates in the blood is always eliminated as such, i.e. that 

 which passes with the blood directly to the kidneys, and thus 

 escapes further decomposition. 



The mean value of the fraction of uric acid excreted is approxi- 

 mately constant for each individual ; so that in every case there is 

 an integral factor by which the quantity of uric acid eliminated 

 must be multiplied, in order to calculate approximately the total 

 quantity of uric acid that enters the vascular circulation. 



This constant integral factor is the same in man even for 

 different individuals, while in carnivora there may be individual 

 differences. It varies, on the contrary, very much in the different 

 species of mammalia ; carnivora eliminate only about -^ or -^ of 

 the uric acid which reaches the circulation in an unaltered form ; 

 rabbits excrete a larger amount, about ^ ; man, as a rule, fully \. 

 These striking differences evidently depend on the varying number 

 and capacity of the organs which destroy uric acid in the different 

 species of animals. 



IV. Creatinine, as we have seen, is one of the principal nitro- 

 genous constituents of urine. The amount excreted in man in 24 

 hours varies considerably according to Neubauer from 0'6 to T3 

 grms. ; according to Johnson from 1 -I 7 to 2 g l grms. ; according to Hof- 

 mann from 0'5 to - 9 grms. In young and robust individuals Grocco 

 as a rule obtained 0'98 grm. on an average, while in old people of 

 70 only 0'45 grm. was obtained. But the amount varies greatly 

 with the diet. We saw in fact that in the healthy young man on 

 whom Bunge experimented 2*16 grms. creatinine were obtained 

 with an exclusively flesh diet, and only 0'91 grm. on a regimen 

 consisting entirely of bread. 



The creatinine of the urine is certainly derived from the 

 creatine of the muscles, from which it differs only by the 

 absence of one molecule of water. According to Voit and Meissner, 

 a small quantity of creatine is always present in the urine of 

 mammals along with the creatinine ; this increases when the urine 

 secreted has an alkaline reaction. It is further to be noted that 

 the reciprocal transformation of these two substances by hydration 

 or dehydration is very easy. In an acid solution the creatine is 

 dehydratised and converted into creatinine ; in an alkaline solution 

 the opposite occurs by hydration. 



Crealine is the most abundant nitrogenous katabolic product 

 of the proteins in the body. In the muscles alone creatine is 

 present in a quantity of about 3 per cent, and the muscles of 

 adult man as a whole contain about 90 grms. of this substance. 

 Seeing that urea, of which 30-40 grms. are daily excreted with 

 the urine, is present only in small quantities in the blood, and 



