178 Creatinine and Creatine in Blood 
nately the opportunity of collecting such a series has not yet 
arisen.” 
There is no evidence in any of the groups that the variations 
of the plasma creatinine are definitely related to the age of the 
subject, at any rate within the limits of 12 to 55 years. 
Creatinine of Whole Blood and Its Distribution. 
In each of the 60 pairs of preformed creatinine determinations 
included in the table the whole blood yielded a higher value than 
the plasma. As far, therefore, as the immediate outcome of the 
analysis is concerned, our original report” receives here the fullest 
corroboration. If the colorimetric method were of the same ac- 
~ curacy in blood asin plasma, it would follow at once that, as we 
formerly announced, the creatinine of the blood is chiefly conéen- 
trated in the corpuscles. Unfortunately the condition of equal 
accuracy is not fulfilled. We have recently,“ on a careful ex- 
amination of the method, convinced ourselves that, as Wilson and 
Plass® had already assumed, the values reported for whole blood 
are an exaggeration of the truth. The extent of the exaggeration 
we found to vary with the individual instance and the particular 
technique employed. With the original technique of Folin," 
modified only by the use of standard curves!® in the interpretation 
of the colorimeter readings, the error, as we estimated it, amounts 
on the average to about 50 per cent of the quantity actually pres- 
ent. While therefore it is not possible to apply to each of the 
single determinations in our table a uniform correction, we are 
in a position to correct the average of any group of determina- 
tions in which the blood was not laked. Two such averages 
appear in Table I; one is that of 17 out of the 30 results in Group 
I, the other that of 27 (including the above 17) out of the total 
60. The two averages are practically identical (1.57 and 1.58). 
If these are 50 per cent in excess of the true average, the latter 
will be found by deducting from each one-third. This gives a 
_ corrected average of 1.05 for both cases. 
26 Plass (Bull. Johns Hopkins Hosp., 1917, xxviii, 137) states that the 
serum creatinine of women in purturition is the same as that of normal 
non-pregnant women, which again is somewhat lower than in normal 
men; but detailed data in support of these statements are not presented. 
e 
