A. Hunter and W. R. Campbell 17] 
mulation of creatinine in the blood has shown itself to be a use- 
ful index of renal insufficiency; but we are as yet unaware whether 
the excess present in the circulation of a nephritic permeates all 
the elements of the blood, or accumulates in the plasma alone. 
If the latter alternative should prove to be correct, the varia- 
tions of the plasma creatinine in kidney disease would be even 
more striking than those of the whole blood creatinine, and would 
form a still more delicate index of the organ’s capacity to excrete. 
A separate study of plasma and whole blood creatinine and 
creatine in different pathological conditions might even reveal 
significant variations in the permeability of the corpuscles for 
these substances. 
It was with these considerations in mind that we undertook 
recently to add creatinine and creatine to the list of blood con- 
stituents with more or less definitely established distribution. 
In a preliminary communication,” in which each aspect of 
our interest in the problem was distinctly indicated, we have 
already presented an abstract of our earliest results. This con- 
stituted, as far as we have been able to discover, the first pub- 
lished contribution to the subject in relation to human, or in- 
deed mammalian blood; although some data upon the distribu- 
tion of creatinine and creatine in fish blood were simultaneously 
communicated by Wilson and Adolph.§ Among the conclusions 
which we thought to be justified by our observations the chief 
was that both in creatinine and in creatine the corpuscles are 
under nearly all conditions richer than the plasma. So long as 
the reliability of our methods was taken for granted no other con- 
clusion was possible. A continuation of the work along the origi- 
nal lines did nothing to modify the general tendency of our 
analytical results, but it gradually engendered doubts concerning 
their real significance. These doubts were not a little accentu- 
ated by the work of Wilson and Plass,!% who, dealing a little 
later with the problems upon which we were engaged, confirmed 
in a general way our view regarding the distribution in human 
blood of creatine, but upon that of creatinine reached a different 
12 Hunter, A., and Campbell, W. R., J. Biol. Chem., 1917, xxix, p. 
XVlil. 
18 Wilson, D. W.; and Plass, E. D., J. Biol. Chem., 1917, xxix, 413. 
