CH. X.] BLOOD SUGAR. 253 



procedure is adopted if the standard solution of picramic acid is 

 used. The two solutions are now compared in a colorimeter (see 

 p. 385), the standard being set at 15 mm. 



Calculation. 2 cc. of blood are taken, diluted to 25 cc. and 8 cc. 

 of the nitrate taken. The amount of blood actually used for the 



o 



test is therefore x 2 = 0-64 cc. 

 25 



Since the colorimeter readings are inversely proportional to 

 the concentrations of glucose 



mg. glucose in 0-64 cc. blood Reading of " S " 



0-64 (i.e. mg. glucose in standard) Reading of " B " 



"S" 0-6, 

 r7 B T ' X o^ 

 Reading of " S " 



c . ,,, , Reading of "S" 0-64 



So glucose in I cc. of blood = - x - - mg. 



Reading of " B " 0-64 



So gram, of glucose in 100 cc. blood = 



Reading of " B " x 10 



This is for a dilution of " B " to 12-5 cc. Should the dilution 

 exceed this, a correction must be applied. Thus, if 7-5 cc. of water 

 are added beyond the 12-5 mark, the result must be multiplied by 

 12-5 + 7'5 = _ = I>6 

 12-5 12 -5 



NOTE. Benedict thinks that in advanced nephritis it might be necessary 

 to modify the procedure owing to the presence of interfering substances, such 

 as creatinine. His original paper should be consulted for details. 



312. The micro-analysis of sugar in blood by Bang's method. 



Principle. A few drops of blood are drawn up on a piece of 

 absorbing paper, the amount taken being determined by measure- 

 ment or by weighing with a torsion balance. After drying, a boiling 

 acidified solution of potassium chloride is added. The proteins are 

 coagulated and the glucose that diffuses out of the paper is estimated 

 by an indirect method. 



Solutions and Apparatus required. 



i. Stock copper solution. In a litre flask place 700 cc. of boiled out, 

 cold distilled water. Warm to about 30 C. Add 160 grams, of pure powdered 

 potassium bicarbonate. When dissolved, add 66 grams, of pure potassium 

 chloride. Cool and add 100 grams, of potassium carbonate. Then 100 cc. of 

 a 4 -4 per cent, solution of pure crystalline copper sulphate. Allow to stand 



