306 PHYSIOLOGICAL CHEMISTRY 



Calculation. In connection with the calculation it is to be 

 noted (a) that the blood nitrate taken corresponds to 2 c.c. of 

 blood, (b) that the standard is diluted to twice the volume of 

 the unknown, and (c) that the standard used contains 0.1 or 0.2 

 mg. of uric acid. The blood nitrate from blood containing 2.5 

 mg. of uric acid will be just equal in color to the weaker stand- 

 ard. Twenty times 2.5 divided by the reading of the unknown 

 gives, therefore the uric acid content of the blood when the 

 weaker standard is set at 20 mm. 



The two standards recommended were adopted on the basis 

 of the experience gained from the analysis of more than 150 

 different samples of human blood. The uric acid may sink to 

 as low as 1 mg. of uric acid per 100 c.c. of blood. It seems 

 hardly worth while to prepare a third and weaker standard 

 regularly in order to provide for such low acid values. A stand- 

 ard corresponding to the color obtained from 1.25 mg. of uric 

 acid per 100 c.c. of blood can be prepared within a couple of 

 minutes as follows: Transfer 1 c.c. of 10% sulphite solution, 

 3 c.c. of 20% sodium carbonate, 2 c.c. of the acidified sodium 

 chlorid, 0.5 c.c. of the sodium cyanid solution, and 25 c.c. of the 

 weaker one of the two regular standard solutions already on 

 hand. Dilute to 50 c.c. and mix. Or, simply add 5 c.c. of 20% 

 sodium carbonate to 25 c.c. of the regular weaker standard, and 

 dilute to 50 c.c. 



If a low uric acid value is expected, an alternate procedure 

 is to dilute the unknown to a final volume of 10 c.c. with corre- 

 sponding reduction in the amount of the reagents used. 



Special attention should perhaps be called to one small yet 

 essential variation in the process for developing the blue uric 

 acid color, a variation made necessary by the use of sodium sul- 

 phite. The uric acid reagent must invariably be added after, 

 and not before, the addition of the sodium carbonate, because in 

 acid solution the sulphite will itself give a blue color with phos- 

 photungstic acid. 



Blood Sugar. (Folin and Wu : Jour. Biol. Chem., xli, 368, 

 March, 1920.) Sugar Reagent. Transfer to a liter beaker 35 



