EXISTENCE OF FREE SUGAR IN BLOOD 207 



actions peculiar to the carbohydrates in colorimetric estima- 

 tion of the blood sugar. Wacker has elaborated a method 46 

 which utilizes a sensitive red color reaction given by 

 p-phenylhydrazinsulphonic acid with carbohydrates in 

 presence of alkali (also with a number of alcohols and 

 aldehydes.) By comparing the red color with a color scale 

 worked out from a standard sugar solution the method is 

 said to successfully differentiate as small amounts as 0.05 

 mg. of glucose and too requires only small quantities of 

 blood (about 10 to 15 drops). In view of certain inherent 

 sources of error 47 , the method is of doubtful availability. 



Existence of Free Sugar in the Blood. It has been fre- 

 quently asked whether the blood sugar is present in the 

 blood free or in colloidal combination, as many authors have 

 concluded from a variety of physiological and analytical 

 observations (particularly from the fact that sugar, which 

 diffuses readily, does not normally pass through the renal 

 filter). Primarily F. Schenk, in connection with his pioneer 

 work on the sugar of the blood, concluded because of its 

 diffusibility that the sugar is not combined in any way with 

 albuminoid substances, but that it exists free in the blood. 

 Further observations in the same line have been published 

 by Arthus, and, too, by Asher, 48 who has been able to prove 

 that diffusion of sugar takes place when, instead of water, 

 a like sample of blood, but previously freed from sugar by 

 fermentation, is used as the outer fluid. Finally, Michaelis 

 and Eona 49 have shown in detail how the sugar proportions 

 in an isotonic salt solution may be prepared so that in 



40 L. Wacker (Wiirzburg), Zeitschr. f. physiol. Chem., 67, 197, 1910; 

 L. Wacker and F. Poly, Deutsch. Arch. f. klin. Med., 100, 567, 1910; 102, 597, 

 1911. 



47 Forschbach and S'everin (Minkowski's Clinic, Breslau), Centralbl. f. 

 Stoffwechselkr., 6, 54, 1911. 



48 L. Asher and R. Rosenfeld (Berne), Biochem. Zeitschr., 8, 351-358, 1907; 

 consult therein Literature; consult also the objections of E. Pfliiger, Pfliiger's 

 Arch., Ill, 217, 1907. 



48 L. Michaelis and P. Rona, Biochem. Zeitschr., 14, 476, 1908, and earlier 

 contributions. 



