A. Hunter and W. R. Campbell 173 
the figures yielded by Group I possess a rather better claim than 
the others to be regarded as standards. The patients of Group 
II were not exactly in the best physical condition, nor were they 
living under altogether normal circumstances; while, with ref- 
erence to Group III, we cannot at present be certain that even a 
| normal pregnancy is entirely without effect upon the relations 
we arestudying. The evidence furnished by Groups II and III 
is therefore to be taken as suggestive or confirmatory rather 
than conclusive in itself. 
Methods. 
The blood was taken from a superficial arm vein by means of 
& syringe, and its coagulation was prevented by the prompt 
addition of 20 per cent potassium oxalate in as nearly as possible 
the proportions prescribed by Folin.= The plasma was imme- 
diately separated from a portion by centrifugation. While this 
was being done, the subject was usually required to provide a 
specimen of urine. The analyses planned were then carried out 
with the briefest possible delay. They included the determi- 
nation of total and preformed creatinine in whole blood, plasma, 
and urine, together with the estimation, by means of the simplified 
hematocrit of Epstein,!® of the relative plasma volume in the 
oxalated blood.!” For the creatinine and creatine determinations 
in blood and plasma we employed the methods of Folin,” although 
the technique followed was not always precisely the same. Thus 
in many of our earlier observations we followed the directions of 
Myers and Fine!® in laking the blood before saturating it with 
picric acid; and in our creatine determinations we did not take 
the precaution, which we have Jately’* found to be desirable, of 
so diluting blood and plasma in every case that the same standard 
could-be employed throughout the series. In one respect at 
16 Folin, O., J. Biol. Chem., 1914, xvii, 475. 
16 Hipstein, i A., J. Lab. a Clin. Med., 1915-16, i, 610.” 
17Tn many cases, but not all, we had sufficient bleed to determine 
also the total non-protein nitrogen. It seemed hardly worth while to 
report individually the scattered results thus obtained. It may be stated 
that they ranged from 29 to 40 mg. per 100 cc., and that, as far as they 
went, they revealed no constant relation to the data for creatinine. 
18 Myers, V. C., and Fine, M. S., Chemical Composition of the Blood 
in Health and Disease, Cooperstown, N. Y., 1915, 19. 
