180 Creatinine and Creatine in Blood 
Our minimum is 1.1, our maximum 2.8; if results in puerperal 
women, which appear to be aberrant, are excluded, our maximum 
is reduced to 2.4, or, if we further limit the record to analyses of 
unlaked blood, to 2.1. Now, if it is granted that creatinine is 
uniformly distributed throughout the .blood, the correct cre- 
atinine content of the latter will be given not by the figures just 
quoted, which we believe to exceed the truth, but by those for 
plasma, which we have shown" to be substantially free from 
error. On that basis the normal range of blood creatinine is 
found to be 0.70 to 1.3, with an average of practically 1 mg. This 
range is all but identical with that which may be found among 
results for human plasma reported by. Plass** and by Wilson 
and Plass.4’ It indicates for the true creatinine content of blood 
a somewhat lower general level than the figures of Myers and 
Fine or even of Folin and Denis. It remains, nevertheless, of the 
same order of magnitude as these, and is very far from ap- 
proaching the extraordinarily low estimate of Gettler and Baker.?® 
These authors found that out of 30 bloods 26 contained only 0.1 
mg. or less of creatinine per 100-cc.; and Gettler,®° in a subse- 
quent analysis of 11 other specimens, indicates 0.5 as the upper 
limit of normality, and reports only 5 as having more than 0.1. 
For such results as these we have failed to find either confir- 
mation or explanation. The work of Gettler may be admitted to 
prove (see his Experiment V*°) that the limits of 1.0 to 1.4, as 
found by Folin and Denis, should be corrected to 0.95 to 1.7; 
but that will hardly serve to explain how Gettler and Baker ob- 
tain values as low as 0.1. 
Relation between Plasma and Urinary Creatinine. 
The determination of urinary creatinine was undertaken simply 
as a step in the detection and estimation of creatine, and not 
with any deliberate intention of studying the laws regulating its 
own passage through the kidney. Any such purpose would have 
necessitated the taking of many precautions which for the present 
were neglected. It did, nevertheless, seem possible that even 
29 Gettler, A. O., and Baker, W., J. Biol. Chem., 1916, xxv, 211. 
30 Gettler, A. O., J. Biol. Chem., 1917, xxix, 47. 
