BLOOD ANALYSIS 



279 



taming 2 c.c. of 0.05 N hydrochloric acid as the receiver. ^Xhe-iHustration shows 

 a compact and convenient arrangement for this distillation. 1 



Add to the urease blood filtrate a dry pebble, a drop or two of paraffin oil 

 and 2 c.c. of saturated borax solution. Insert firmly the rubber stopper carrying 

 the delivery tube and receiver and then boil at a moderately fast, uniform rate 

 for 4 minutes. The size of the flame should never be cut-down during the distil- 

 lation, nor should the boiling be so brisk that the emission of steam from the 

 receiver begins before the end of 3 minutes. At the end of 4 minutes slip off 

 the receiver from the rubber stopper and let it rest in a 

 slanting position while the distillation is continued for i 

 more minute. Rinse the lower end of the delivery tube 

 with a little water and cool the distillate with running water 

 and dilute to about 20 c.c. Transfer 0.3 mg. N (3 c.c. of 

 the standard ammonium sulphate solution) to a 100 c.c. 

 volumetric flask and dilute to about 75 c.c. Nesslerize, 

 using 10 c.c. of Nessler's Solution for the Standard, and 

 2.5 c.c. for the unknown in the test tube. Dilute both to 

 volume and make the color comparison.^) 



Calculation. Divide 20 (the height of the standard in 

 mm.) by the colorimetric reading and multiply *by 15. 

 This gives the urea nitrogen in mgs. per 100 c.c. of blood. 

 In explanation of this calculation it is to be noted that the 

 unknown representing 0.5 c.c. of blood, is Nesslerized at 

 25 c.c., whereas in the case of the non-protein nitrogen it 

 is Nesslerized at a volume of 50 c.c. The same colori- 

 metric reading, therefore, represents only one-half as much 

 nitrogen in the urea determination as in the non-protein 

 nitrogen determination. 



Urea Determination by Means of the Autpclave. When 

 a large number of urea determinations are to be made or ma y be cut along the 

 when creatin determinations are also made, it is sometimes side of the stopper of 



convenient to decompose the urea of the blood nitrate by the receiving tube to 



,. . . . , ,,, . permit the escape of 



heating under pressure. To 5 c.c. of the blood nitrate in a s team. 



large test tube add i c.c. of normal hydrochloric acid, cover 

 with tin foil and heat to 150 for 10 minutes. Distil off the ammonia exactly as 

 in the preceding process, except that 2 c.c. of 10 per cent sodium carbonate must 

 be substituted for the borax, because of the added hydrochloric acid. 



Aeration Process in Urea Determination. The ammonia formed from the 

 blood urea by urease, or by heating under pressure, can, of course be, driven 

 into the receiver by an air current plus an alkali, instead of by the distillation 

 process described above. The aeration process gives perfectly reliable results, if a 

 good air current is available. 



To the decomposed blood nitrate in a large test tube add a little paraffin oil 

 and i or 2 c.c. of 10 per cent sodium hydroxide. Connect with a smaller test tube, 

 marked at 25 c.c., and containing 2 c.c. of 0.5 N hydrochloric acid. The connection 

 is made as in the aeration process for urea in urine. Pass the air current through 

 rather slowly for i minute and then nearly as fast as the apparatus can stand for 



FIG. 88. APPA- 

 RATUS FOR DISTIL- 

 LATION OF AMMONIA 

 FROM UREA. A, 

 FIRST POSITION. B, 

 SECOND POSITION. 



(Folin and Wu: 

 Jour. Biol. Chem., 



1 Watson and White have suggested a modification of this apparatus. See Jour. Biol. 

 Chem., 45, 465, 1921. 



