182 MARSHALL-BANKS— NEW NEPHELOMETER. [April 23, 



work of rather an empirical nature along biochemical lines. Kober 

 in one of his papers suggested the possibility of a nephelometric 

 determination of albumin in urine, and a turbidimetric method for 

 the same has been developed by Folin and Denis/' We therefore 

 decided to apply our instrument to this problem. The standard was 

 prepared from fresh normal human serum as recommended by Folin 

 and Denis, and was standardized by nitrogen determinations and 

 also by gravimetric determination of the heat coagulable proteins. 

 Difficulty was encountered at the start in comparing in the 

 nephelometer albumin precipitated in the urine with that precipitated 

 in the solution of standardized blood serum, on account of the dif- 

 ference in color due to the urinary pigments. In order to eliminate 

 this interference of color, and also to obtain identical conditions of 

 precipitation for both urine and standard, two equal portions of 

 the urine of from 0.3 c.c. to 10 c.c. depending upon the quantity of 

 albumen present, were taken. To one of these a known amount of 

 standard was added (about 0.5 c.c. of 0.4 per cent, solution of serum 

 protein). Both were then diluted to 75 c.c. with water and finally 

 made up to 100 c.c. by the addition of a 7.5 per cent, solution of 

 sulpho-salicylic acid. This gave a final concentration of 1.87 per 

 cent, sulpho-salicylic acid, while the amount of protein varied from 

 2 to 5 mg. in 100 c.c. The resulting opalescent solutions were then 

 compared in the nephelometer, the tube containing the urine plus 

 standard being placed under the tapered slot. The light from this 

 tube was then progressively diminished by adjustment of the slotted 

 plate until photometric balance was obtained. From a scale with 

 suitable vernier the position of the plate was read. As the theory 

 has not advanced far enough as yet to permit of a purely formula- 

 tive interpretation of the readings, the ratio of the concentrations of 

 the two suspensions was determined from a curve. This curve had 

 been obtained by plotting against the concentrations the scale read- 

 ings obtained when known ratios of serum, made up with albumin 

 free urine and precipitated with sulpho-salicylic acid under identical 

 conditions, were compared. From the ratio R determined by means 

 of the curve, the amount X of albumin originally present in the urine 



was found by the formula R=^ c^— — where n is the amount of 

 5 Folin and Denis, Jour. Biol. Chem., XVIIL, 273, 1914. 



