A New Blood Sugar Method

The purpose of the investigation described in this paper was to develop a method for the determination of sugar in 0.1 cc. of blood.Heretofore I have not been much interested in so called micro methods of blood analysis, because one usually wants to determine more than one blood constituent, and whenever that is the case it is more practical to use larger quantities of blood and make the several determinations on one filtrate.The sugar problem is, however, so distinct from the nitrogen problem that it would seem to merit separate consideration.In this method I have abandoned the use of copper solutions.The sugar is oxidized with alkaline potassium ferricyanide, and the ferrocyanide produced is measured calorimetrically as Prussian blue.The color obtained from 0.04 mg. of glucose in a 25 cc.tube is quite as deep as the color obtained from 0.2 mg. of sugar in the Folin-Wu method.Two separate determinations, therefore, can be made on the extract from 0.1 cc. of normal blood, and several determinations can be made when the extract is obtained from diabetic bloods with high sugar contents.Reagents.1. Dilute Tungstic Acid Solution.-Transfer20 cc. of 10 per cent sodium tungstate solution to a volumetric liter flask.Dilute to a volume of about 800 cc.Then add with shaking 20 cc. of $ N sulfuric acid and dilute to volume.Add a little toluene to prevent the growth of moulds.2. Potassium Ferricyanide Solution.-Dissolve 1 gm. of C.P. potassium ferricyanide in distilled water and dilute to a volume of 500 cc.The major part of this solution should be kept in the dark.