BLOOD ANALYSIS 285 



This cooling is not essential and, in case of one or two determinations only, may 

 be omitted. In a large series of determinations it is probably best to use it. The 

 important point is that the standard and the unknowns should not only be heated 

 the same length of time but should also have substantially the same temperature 

 when the acid reagent is added. The maximum color develops faster in hot solu- 

 tions; but if a reasonable uniformity of condition is maintained it makes no differ- 

 ence whether the color comparison is made at the end of 5 minutes or at the end of 

 i hour. 



Reading of Standard mg. of glucose in standard 



Calculations. -X - - = Grams 



Reading of Unknown 2 



of glucose per 100 c.c. of blood. 



Interpretation. ^Normal blood contains from 0.08 to 0.12 per cent, 

 of glucose. In mild diabetes values of from 0.14 to 0.30 are obtained, 

 and in severe diabetes values up to 1.2 per cent. Hyperglycemia is 

 found also in nephritis and hyper thy roidism. Hypoglycemia has been 

 noted in hypo thy roidism, Addison's disease, muscular dystrophy, 

 etc. Normally sugar begins to appear in the urine when the blood 

 concentration reaches 0.15 to 0.18 per cent. 



The concentration of sugar in the corpuscles is usually a little lower 

 than in the plasma and more variable. Plasma determinations may, 

 therefore, possess some advantage over whole blood determinations. 1 

 For sugar tolerance test see page 290. 



8. Determination of Chlorides. 2 Principle. The chlorides are 

 precipitated from the blood filtrate by means of silver nitrate in the 

 presence of nitric acid and the excess of silver titrated with standard 

 sulphocyanate solution, using ferric ammonium sulphate as an indicator. 



Procedure. Because of the slight variations in the chloride content of blood, 

 dilution in preparation of protein-free filtrates should be made very carefully 

 and volumetric flasks may be preferred. 



Pipette 10 c.c. of the protein-free filtrate into a porcelain dish. Add with a 

 pipette 5 c.c. of the standard silver nitrate solution 3 and stir thoroughly. Add 



1 Wishart, M. B.: Jour. Biol. Chem., 44, 563, 1920. 



2 Whitehorn, J. C.: Jour, Biol. Chem., 45, 449, 1921. This method is applicable to 

 plasma and whole blood. The same principle was used by Rieger: /. Lab. Clin. Med., 

 6, 44, 1920-21. Rappleye: Jour. Biol. Chem., 35, 509, 1918, showed that the Volhard 

 method could be applied directly to plasma without prior removal of protein. Van Slyke 

 and Donleavy: Jour. Biol. Chem. 37, 551, 1919, showed that the iodometric method of 

 McLean and Van Slyke: Jour. Biol. Chem., 21, 361, 1915, could also be used in this way. 

 Austin and Van Slyke: Jour. Biol. Chem., 41, 345, 1920, used the picric acid precipitation 

 in the case of whole blood. Myers and Short: Jour. Biol. Chem., 44, 47, 1920, have com- 

 bined the picric acid precipitation of protein with the Volhard titration to produce a con- 

 venient and satisfactory method. Wetmore; Jour. Biol. Chem., 45, 113, 1920, uses copper 

 hydroxide precipitation and the Volhard titration. 



3 Preparation of Reagents. Dissolve 4.791 gm. of C.P. silver nitrate in distilled water. 

 Transfer this solution to a liter volumetric flask and make up to the mark with distilled 

 water. Mix thoroughly and preserve in a brown bottle, i c.c. = i mg. Cl. (It is to be 

 noted that the silver nitrate and nitric acid are not added to the protein-free nitrate simul- 

 taneously. To do so may result in the mechanical enclosure of silver nitrate solution 

 within the curds, and a consequent error in the positive direction.) 



Because sulfocyanates are hygroscopic, the standard solution should be prepared 

 volu metrically. As an approximation about 3 gm. of KCNS or 2.5 gm. of NEUCNS should 



