252 THE BLOOD. [CH. X. 



3. Sodium carbonate solution. Dissolve 200 grams, of pure anhydrous 

 sodium carbonate in hot distilled water and make the volume up to i litre. 

 Filter when cold. The solution should be kept in a warm room, as it may 

 crystallise out if the temperature gets very low. 



4. Test-tubes graduated at 12-5 "and 25 cc. A suitable internal 

 diameter is f inch. It is convenient to have one tube engraved with " S " 

 for the standard and one with " B " for the blood. 



5. A 25 cc. volumetric flask. If this is not to hand, one of the graduated 

 tubes can be used. 



6. Ostwald pipettes of i and 2 cc. (See fig. 48.) 



7. A colorimeter. (See p. 384.) 



Method. 2 cc. of blood are drawn into an Ostwald pipette, 

 containing a trace of powdered potassium oxalate to prevent coagu- 

 lation. The blood must be drawn under strict antiseptic precau- 

 tions. Discharge the blood into a 25 cc. volumetric flask (or gradu- 

 ated tube), and wash the pipette out twice with distilled water, 

 adding the washings to the flask. After standing for a couple of 

 minutes, with gentle agitation, to lake the blood, add the picric- 

 picrate mixture to the mark, and thoroughly shake the mixture. 

 After standing for a minute or two* the mixture is poured on to a 

 dry filter and the clear filtrate collected in a small dry flask. Measure 

 8 cc. of the filtrate into one of the " B " calibrated tubes, add i cc. 

 of the sodium carbonate solution, mix, and plug with cotton wool. 

 If glucose is being used as a standard, measure i cc. of the diluted 

 solution mentioned above (i.e. 0-64 mg. glucose) into one of the 

 " S " tubes, using an Ostwald pipette. Add 3 cc. of distilled water, 

 4 cc. of the picric-picrate mixture and i cc. of the sodium carbonate. 

 Mix and plug with cotton wool. Have a beaker or can of water 

 boiling. Immerse both tubes in this and note the time. After 

 exactly ten minutes' heating in the bath, the water of which must be 

 kept boiling the whole time, remove the tubes and cool thoroughly. 

 Dilute the standard to the 12-5 cc. mark with distilled water. 

 Dilute the " B " tube to the same mark and compare the colours of 

 the two solutions. If that of " B " is much greater than that of 

 " S," the " B " tube can be treated with 2-5, 5, 7-5, 10, or 12-5 cc. 

 of water, until the colours of the two solutions appear to be about 

 the same, making a note of the amount of water added. The same 



* The method can be interrupted at this stage, the picric acid preventing 

 glycolysis. 



