176 Creatinine and Creatine in Blood 
the maximum from the calculation, 0.86. It is clear that the 
hospital inmates selected as normal individuals presented in gen- 
eral an unmistakably lower level of plasma creatinine than thé 
active male students. 
With respect to the cause or causes of this difference we can 
only speculate. Group II, unlike Group I, included a consider- 
able proportion of females. Several of its members showed an 
abnormally high relative plasma volume, possibly indicative of a 
certain degree of dilution of the blood. Three-fourths of them 
were confined to bed, and the others were at least leading a 
sedentary existence. All, it is safe to assume, were eating less 
than the more actively employed members of Group I, and some, 
it is known, were on a very restricted diet. It is not yet possible 
to decide what actual influence any or all of these circumstances 
may have exerted upon the plasma creatinine of the group as a 
whole. Certainly neither the first mentioned nor the second 
will wholly explain its relative lowness. For, while it is true 
that the average for the females of the group is lower than that 
for the males, and even that within each subgroup the maxi- 
mum for women is lower than the minimum for men, yet the 
males, considered apart, still yield distinctly less creatinine than 
those of Group I; and, although dilution of the plasma doubtless 
may diminish its creatinine concentration, there is evidence on 
the one hand (Cases 58, 59, 60) that it does not always do so, 
and on the other (Cases 8, 5, 36) that a plasma creatinine below 
the average may be encountered in blood which is the reverse of 
hydremic. Of the other two possible factors suggested, low 
diet and enforced inactivity, the latter is the one which seems 
the more likely to be of general importance; for the production 
of creatinine within the body is independent of the diet but 
intimately related to the condition of the muscular tissues.” 
It may well be assumed that few, if any, of our hospital sub- 
jects maintained themselves, while confined to bed, upon the 
same plane of muscular efficiency as the members of Group I. 
Provisionally therefore we are inclined to ascribe the low plasma 
creatinines of Group II partly to the female sex of some of its 
members, but largely to lack of exercise in its effect upon mus- 
4 Shaffer, P. A., Am. J. Phystol., 1908-09, xxiii, 1. 
