Creatinine and Creatine. 393 



On comparing the excretion of creatinine during the first 12 hours of the day 

 with the total nitrogen (see table 198) it is seen that while in experiment No. 

 75 on the average 57.7 per cent of the total nitrogen for 24 hours is excreted 

 between 7 a. m. and 7 p. m., but 51.6 per cent of the preformed creatinine is 

 excreted during the same period. Furthermore, while the proportion of 

 nitrogen excreted during the first 12 hours of the day remains quite constant 

 on all days of the fast, the proportion of creatinine has a distinct tendency to 

 diminish as the fast progresses. 



Proportions of creatine nitrogen and total creatinine nitrogen excreted. The 

 proportions of the total urinary nitrogen derived from creatinine nitrogen and 

 creatine nitrogen are of interest. The amounts of total nitrogen, total creatine- 

 nitrogen and of total creatinine-nitrogen, as well as the proportions, are given 

 in table 205. 



The absolute amounts of total creatinine-nitrogen vary from 0.294 gram to 

 0.778 gram. While these wide variations are noted with different individuals, 

 with the same individuals the absolute amount is relatively constant. The 

 nitrogen of creatine is inappreciable save on the later days of the longer fasts, 

 the highest amount observed being on the sixth day of experiment No. 75, 

 0.188 gram. The relative constancy in the creatinine-nitrogen from day to day 

 is not accompanied by a similar constancy in the total nitrogen excretion, 

 hence the proportion of creatinine-nitrogen in total nitrogen varies somewhat. 

 In experiment No. 75, there is a distinct tendency for the proportion of 

 creatinine-nitrogen to increase as the fast progresses, while in experiment No. 

 77 the reverse is true. An inspection of the figures shows that in almost every 

 instance the variation is due to the fluctuations in the total nitrogen of the 

 urine rather than to the nitrogen of creatinine. 



The proportion of creatine nitrogen in the total nitrogen is exceedingly 

 small on all save the later days of fast. The highest per cent observed was 1.75 

 on the sixth day of experiment No. 75. It is highly probable that errors in 

 determination may account for the minute quantities of creatine found on the 

 first day of fasting. 



Relation of total creatinine excreted to body-weiglit. As Folin has pointed 

 out, the total creatinine excretion is relatively unaffected by the total nitrogen 

 excretion when creatinine-free diets are consumed. The total creatinine elimi- 

 nation does vary, however, according to the individual, and in general, with 

 body-weight. With persons of the same body-weight, nevertheless, marked 

 differences in the proportion of body fat, and height, may result in marked 

 variations in the amount of creatinine excreted per kilo of body-weight. For 

 purposes of comparison, the data regarding the body-weight and the total 

 creatinine, as well as the total creatinine per kilo of body-weight, are given in 

 table 206. 



