A. Hunter and W. R. Campbell Was 
cular tone. If the associations thus suggested are correct, a 
low plasma creatinine would be characteristic of such cases as 
might be expected to have a low creatinine coefficient; and it 
is of some interest that according to Shaffer” there is found under 
similar conditions a smaller concentration than usual of creat- 
inine in the muscles also. The possible influence of prolonged in- 
action upon the plasma creatinine could obviously be put to 
experimental proof; and.a further examination of the question 
is accordingly in contemplation. Meanwhile it may be of 
practical clinical importance to note that a plasma creatinine 
of 1.2 mg., which would be perfectly normal in an active sub- 
ject, already verges upon the pathological for one who is resting 
in bed. 
The idea, suggested by the results within Group II, that fe- 
males have naturally a lower plasma creatinine than males, 
receives additional support from the data furnished by the sub- 
jects of Group III. These, as already stated, were all females, in 
whom pregnancy constituted the only deviation from normality. 
The ten plasmas included in this group contained amounts of 
- creatinine ranging from 0.71 to 1.2, seven of them falling below 
1.0 mg., and the average of all reaching only 0.92. These fig- 
ures certainly occupy a lower general level than those of Group 
I, with their minimum of 0.80 and their average of 1.1. It 
may, of course, be objected, that women advanced in pregtiancy, 
even if they are still taking a certain amount of exercise, can 
hardly be regarded as physiologically comparable with active 
young men. The comparison, at the end of Table I, of the 
general average for all males (1.04) with that for all females (0.87) 
has to be regarded with similar reserve. It is really only within 
Group II that difference of sex is not obviously complicated by 
some other circumstance of possible consequence. We are 
therefore not yet prepared to state with conviction, although we 
regard it as exceedingly probable, that the sex effect indicated 
by our figures has an existence independent of all other factors. 
To determine finally its actual importance, it would be necessary 
to possess for comparison with the data of Group I a series of 
observations upon active and healthy young women; unfortu- 
25 Shaffer, J. Biol. Chem., 1914, xviii, 525. 
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