404 THE METABOLISM OF THE PURTN BODIES 



That the excretion of endogenous purins is variable for dif- 

 ferent individuals, has been accepted by most of the modern 

 workers, but is denied by Loewi ( 14> 15> 1G ). His conclusions are 

 based mainly on observations on three persons who were of about 

 the same age, and each of whom received the same mixed diet. 

 The uric acid excretion in the three persons was the same, and 

 from this Loewi concludes that similarly fed men in similar 

 conditions of metabolism excrete the same amount of uric acid, 

 and that this latter is dependent on the food alone, and does 

 not show any difference due to individuality. It must be evi- 

 dent, however, that it by no means disproves Burian and 

 Schur's statement, that Loewi should have happened to observe 

 three persons excreting, on the same diet, the same amount 

 of uric acid. In the collected cases, which we have given 

 above, ten out of eighteen had the same endogenous purin 

 excretion, and if to any three of these ten persons the same 

 amount and kind of purin were given in the food, their total 

 purin excretion would be the same, for, as we shall see later, 

 exogenous purins reappear in the urine to the same extent in all 

 individuals. 



Loewi states further that it is incorrect to try and measure 

 the endogenous uric acid on a purin-free diet, because the 

 tissues, in such a case, will be starved of nuclein, and will, 

 consequently, not destroy so much of it as they would 

 were an adequate supply furnished them from without. This 

 presupposes, of course, that tissue nuclein is regenerated from 

 food nuclein, and, in such a case, Loewi' s argument would be 

 correct enough : Burian' s endogenous purins would represent a 

 starvation amount, and on giving nuclein in the food the 

 first thing to happen would be that the starving tissues 

 appropriated some, at least, of the nuclein for reconstruction, 

 and the endogenous factor would fall. Loewi's contention is, 

 however, absolutely groundless, for tissue nuclein is not built 

 up out of food nuclein, but out of a nuclein-free substance, 

 even when nuclein rich food -stuffs are also present (Burian and 

 Schur). 



Although variable for different individuals, the endogenous 

 purin excretion seems to be constant for any one person , provided lie 

 be living under the same physiological conditions. Even a consider- 

 able disturbance of nitrogen equilibrium appears to have no 



