190 Creatinine and Creatine in Blood 
is the rule. Their evidence, unfortunately, is in some respects 
as defective as our own. The number of human cases they re- 
port is but nine in all,.and in none of them was the urine actu- 
ally analyzed. A final settlement of the question of a creatine 
threshold must therefore await the. collection, by methods of 
unquestioned accuracy, of data more complete and reliable than 
any that we yet possess. 
SUMMARY. 
1. The creatinine content of normal human blood plasma 
ranges under different conditions from 0.70 to 1.3 mg. per 100 
cc., the average for 60 specimens examined being 1 mg. 
2. It is practically certain that the creatinine of normal blood 
. is distributed through corpuscles and plasma in uniform con- 
centration. 
3. The figures given for plasma indicate, therefore, also the true 
creatinine content of whole blood. 
4. The blood creatinine is apt to be lower in females than in 
males, and lower in subjects deprived of exercise than in those 
leading an active life. It is suggested that the blood creatinine 
is related to muscular development in much the same way as the 
creatinine coefficient. 
5. The creatine of the blood is chiefly concentrated in the cor- 
puscles. With the method used exact determinations were un- 
~~ attainable, but it is roughly estimated that the average creatine 
content of the corpuscles lies between 6 and 9 mg. per 100 cc., 
while that of the plasma is not more than 0.4 to 0.6. The blood 
as a whole contains apparently an average of about 3 mg. per 
100 cc. There seems to be more in the blood of females than of 
males. 
6. There is a distinct correspondence between increase of 
plasma creatine and the appearance of creatine in the urine; but 
whether the plasma, in the absence of creatinuria, 1s creatine-free 
or whether there exists a threshold for creatine excretion, has 
not been positive'y determined. If there is a threshold, it is a 
very low one. 
We take this opportunity of thanking the students and instruc- 
tors of Toronto University Medical School who permitted us to — 
