402 THE METABOLISM OF THE PTJRIN BODIES 



It will be noticed that there was no appreciable change in the 

 nitrogen excretion between the first and second periods. Between 

 the second and third periods there was, of course, a temporary 

 disturbance lasting for three days, more nitrogen being excreted 

 than administered, but by the fourth day equilibrium had again 

 been attained, and on changing to the vegetable diet (fourth 

 period) no further disturbance occurred. The necessary con- 

 ditions for a rational measurement of the endogenous purins were 

 thus obtained in Period II., there being here no disturbance in 

 metabolism. 



Turning now to the excretion of purins during these four 

 periods, and taking for this purpose the average of the last three 

 days of each period (since during the first day the previous diet 

 will still have an influence on the urine), we obtain the following 

 values : 



Period I., total purin nitrogen, O339 grm. 

 i, II- ,. ,, 0-202 



III, 0-203 



IV., 0-203 



The endogenous moiety here is obviously 0'202 grm. purin 

 nitrogen ; and the exogenous moiety during the first period 

 0'137 grm. purin nitrogen. The endogenous moiety, it will be seen, 

 is uninfluenced by the nature and amount of the diet, provided 

 always that this is purin-free and is sufficient in amount, and 

 of proper composition to prevent starvation. Chemical analysis 

 has already shown us that the food- stuffs given in the last three 

 periods of this experiment are practically purin-free, and now we 

 have the proof that from the physiological point of view they 

 may be considered entirely so, for did the food -stuffs during these 

 periods contain any appreciable amount of purin, there obviously 

 would have been variations in the amount of purins excreted 

 between Periods II. and III. and Periods III. and IV. 



These findings of Burian and Schur were almost simultane- 

 ously confirmed by Siven, in whose experiments longer periods of 

 time were allowed and greater variations in nitrogen intake brought 

 about, and still with the same constancy in endogenous purin 

 excretion. 



In a series of very complete metabolism observations on men, 

 recently recorded by Folin, it has been noted, among other things, 



