THE METABOLISM OF PROTEIN 625 



years of age. Girls, on the other hand, continue to excrete creatine until 

 about puberty, after which, although ordinarily absent, it reappears in 

 the urine at each monthly sexual cycle, and is present during pregnancy 

 and for some days after delivery. Feeding creatine to children causes 

 it to appear in the urine, accompanied usually by a slight increase in 

 the creatinine. The same results can be observed in women during the 

 monthly periods, when as much as 0.1 gm. may be present, and during 

 pregnancy. Creatine is also present in the urine of most if not all of 

 the other mammalia. Some of these facts are shown in the following 

 table : 



.AGE CREATININE-N CREATINE-N EXCRETED 



IN 24-HR. URINE 



(From Mathews.) 



When creatine is given to an animal that has been kept in a starved 

 condition, most of it seems to disappear. It can not be recovered in the 

 urine either as creatine or as any other nitrogenous metabolite. It seems 

 to functionate more as a food than as a useless substance. The possi- 

 bility that some of it can be destroyed by the intestinal bacteria being 

 admitted, there is nevertheless some justification for the view that the 

 creatine finds a useful function in the anabolic process of the muscles. 



Influence of Complete and Partial Starvation. Although, as we have 

 seen, the creatinine excretion remains constant when the amount of pro- 

 tein in the diet is greatly reduced, yet it does not remain constant during 

 complete fasting or when carbohydrates are entirely withheld from the 

 diet. In fasting it has been found that creatine appears in place of the 

 creatinine which has disappeared, so that if both creatine and creatinine 

 are determined, very little if any diminution will be found to have oc- 

 curred. Fasting, therefore, causes the adult creatine and creatinine 

 metabolism to become like the juvenile metabolism. As pointed out by 

 Mathews, it would be interesting in the light of this observation to see 

 whether other substances, passed in the urine of young animals but ab- 

 sent in that of the adult, would reappear in the urine when the animals 

 were made to fast. In the case of man, for instance, allantoin would be 

 worth investigating in this regard (page 641). 



