BLOOD ANALYSIS 289 



Coagulation of Blood Protein. Transfer the piece of paper to a test-tube and 

 add 6.5 c.c. of boiling acid-potassium chloride solution 1 and let stand half an hour. 

 The clear solution containing the sugar is poured into a 50 c.c. Jena flask the 

 flange of which has been removed. Wash the paper and tube again with 6.5 c.c. 

 of hot salt solution and transfer washings to the flask. Cool. 



Reduction of Cupric Chloride. Attach to the mouth of the flask a piece of 

 tight-fitting rubber tubing about 2 inches long (see Fig. 91), provided with a 

 clamp which permits of shutting off the contents of the flask from the outside air. 

 Now add to the flask i c.c. of the cupric chloride solution. 2 Heat so that the 

 solution is brought to a boil in one minute and 30 seconds (an error of five seconds 

 may be disregarded). Allow to boil for exactly two minutes; at the end of this 

 time tighten the clamp over the mouth of the flask. At the 

 same time remove from the flame and cool at once under the 

 tap for about a minute. 



Titration of Cuprous Chloride Formed. The titration is 

 made with N/2OO iodine solution 3 run in from a very accurate 

 burette (preferably a 2 c.c. burette graduated in 1/50 c.c.). 

 Two or 3 drops of starch solution (preferably soluble starch 4 ) 

 are added as an indicator. During the titration air must be 

 excluded to prevent re-oxidation. This is done by running a 

 slow stream of carbon dioxide from a generating bottle through 

 a small tube which extends nearly to the bottom of the flask. 

 The titration should be carried out against a white background FIG. 91. 



and the end point taken when the blue color persists for 20-30 

 seconds. 



Calculation. The copper and other solutions used in the test bind about 

 o.i 2 c.c. of the iodine solution. This amount must hence be subtracted from 

 the reading. The corrected reading is then divided by 4 to obtain the num- 

 ber of milligrams of glucose in the sample. 



. Example. If 0.68 c.c. of N/2OO I solution were required, - = 0.14 



mg. glucose in the amount of blood used. If 140 mg. of blood were taken for 



analysis the per cent of glucose in the blood would be - X 0.14 mg. = o.i per 

 cent glucose. 



The results obtained by this method are a little higher than those obtained 

 by other reliable methods due to the presence of certain I -binding substances in 

 blood. As these appear to be nearly constant in amount a correction may be 

 applied. To obtain true values for glucose of the blood therefore subtract 

 0.015 per cent from the value obtained as above, o.i pe*r cent 0.015 per cent 

 = 0.085 per cent glucose. 



1 Consisting of 1360 c.c. of saturated KC1 to which is added 640 .c.c. of water and 1.5 

 c.c. of 25 per cent HCL. 



i 2 Copper solution. Introduce into a 1000 c.c. flask 700 c.c. of boiled and cooled water. 

 Warm to about 3oC. and add 160 grams of pure potassium bicarbonate in powder form. 

 When dissolved add 66 grams of pure KC1. Cool and then add 100 grams potassium car- 

 bonate. Finally add 100 c.c. of 4.4 per cent solution of pure crystalline copper sulphate. 

 Let stand a short time, then make to mark with boiled water. Allow to stand a day or so 

 before using. 



3 N/2oo I solution, made fresh each day. Dilute N/io I solution 20 times, or make 

 as follows: Introduce into a 100 c.c. flask 2 grams KI, 1-2 c.c. of 2 per cent KIOj solution 

 and 5 c.c. of N/io HCL Make to mark with boiled and cooled distilled water. 



4 A i per cent solution of Kahlbaum's soluble starch in a saturated KC1 solution. 



19 



