110 METHODS FOR THE ANALYSIS OF BLOOD 



perature of the solutions below 20. In the third stage when the 

 nitric oxide is being absorbed by the permanganate, the Hempel 

 pipette should be shaken not faster than twice per second. This 

 is to prevent the breaking off of small gas bubbles. 



It is especially necessary that in the first stage the removal of 

 ah* be complete. This is assured by shaking the solution in the 

 deaminizing bulb back each time, in this stage, until the bulb is 

 two-thirds filled with nitric oxide. 



SUGAR 



Benedict Modification of the Method of Lewis and Benedict l 



Principle. The red color obtained by heating a glucose solu- 

 tion with picric acid and sodium carbonate is employed as the 

 basis of the colorimetric determination. The blood protein is 

 removed by precipitation with picric acid. 



Procedure. Two c.c. of blood are aspirated through an hypo- 

 dermic needle and a piece of rubber tubing into an Ostwald pipette, 

 a little powdered potassium oxalate in the tip of the pipette pre- 

 venting clotting. (It may be more convenient to draw about 5 c.c. 

 of blood directly into a test-tube containing a little powdered 

 potassium oxalate and removing 2 c.c. portions of this with the 

 Ostwald pipette.) The blood is drawn up a little above the mark 

 and the end of the pipette is closed with the finger. After the 

 rubber tubing and needle are disconnected, the blood is allowed 

 to flow back to the mark and is discharged at once into a 25 c.c. 

 volumetric flask, or into a large test-tube graduated at 12.5 c.c. 

 and at 25 c.c. The pipette is twice rinsed with distilled water, 

 these washings being added to the blood. The contents of the 

 flask are shaken to insure thorough mixing and a consequent 

 laking or hemolysis of the blood, which is practically complete 

 after a minute or two. A solution of sodium picrate and picric 

 acid is added to the 25 c.c. mark (using a few drops of alcohol to 

 dispel foam if necessary) and the mixture thoroughly shaken. 

 After a minute or two (or longer) the mixture is poured upon a 

 dry filter, and the clear nitrate collected in a dry beaker. Exactly 

 8 c.c. of the filtrate are measured into a large test-tube bearing 



Benedict: Jour. Biol. Chem., 1918, 34, 203. Lewis and Benedict: 

 Jpur f Bjpl, Chem., 1915, 20, 61. 



