624 ' METABOLISM 



It should be pointed out that, since the creatine is estimated by an 

 indirect method, there are considerable chances for inaccuracy. Indeed, 

 it has been shown that errors may have been incurred in some of the 

 recent work on account of the fact that when acetoacetic acid is present 

 in the urine it prevents the creatinine from developing its full reducing 

 power on picric acid in the cold, so that when subsequently the urine is 

 heated with acid for the purpose of converting the creatine into creati- 

 nine, the destruction of acetoacetic acid allows the reducing power of the 

 creatinine to develop to full intensity. It is obvious that this would make 

 it appear as if creatine had been converted into creatinine. It is par- 

 ticularly in the urine of diabetic patients, in which acetoacetic acid is 

 present that mistakes are likely to be made. 



Metabolism 



When we come to consider the metabolism of creatine and creatinine, 

 we find that there are remarkably few facts definitely known concerning 

 it. The average amount excreted daily, expressed as the number of milli- 

 grams of creatinine in twenty-four hours per kilogram body weight, 

 is known as the creatinine coefficient (Shaffer). 36 For a lean person this 

 is about 25 mg. ; for a corpulent person, about 20 mg., the difference in- 

 dicating that muscle mass, and not body weight, is the important factor 

 determining the coefficient. Further evidence that this relationship ex- 

 ists is furnished by the fact that in the muscular atrophies creatine ex- 

 cretion is distinctly below normal. It must be the mass of the muscles 

 rather than their activities that is the determining factor, for the creatine 

 excretion does not become increased by muscular exercise. 



Influence of Food, Age, and Sex. Although creatine and creatinine are 

 endogenous metabolites, it must be remembered that, under ordinary 

 dietetic conditions, a part of each is derived from these substances pres : 

 ent in the food. It is important therefore to consider the conditions 

 under which the creatine and creatinine in the food appear in the urine. 

 Regarding creatinine, it is pretty well established that practically all 

 that is taken with the food reappears as creatinine in the urine. Shaffer 

 has, for example, succeeded in recovering 76 per cent of ingested creat- 

 inine in the urine excreted during twenty-one hours following the in- 

 gestion of 0.7 gm. creatinine. 



The conditions for the excretion of creatine are more complex. It is 

 present in the urine of children in considerable amount, but in that of 

 adults only as traces. In the first years of life the creatine in boys' 

 urine may amount to one-half of the total creatine and creatinine, but 

 it becomes gradually less and practically disappears at about seven 



