ALKALI RESERVE OE BLOOD 551 



(37. Bleeding Time. 



Clean the lobe of the ear with ether and puncture with a sterile lancet. As 

 the first drop of blood appears, start a stop watch goinj?. Using the edge of 

 a circle of filter paper, remove the drops of blood as they form. Note the time 

 when no further drop appears. 



Repeat. Compare the clotting time and the bleeding time of the same 

 subject. 



(kS. Haematocrite. 



This apparatus consists of two similar graduated capillary tubes, which, 

 after clipping in a holder, may be spun horizontally by a centrifuge. A 

 small measured quantity of Midler's fluid (Na2S04 - 1 gni. ; K2Cr.07 - 2 gm. ; 

 distilled water, 100 gm.) is placed in a test glass. The same quantity of 

 blood is added. Mix thoroughly with a glass rod. Fix a short length of 

 rubber tubing furnished with a mouthpiece to each of the graduated 

 tubes and suck up sufficient of the mixture to fill the tubes. Place them in 

 a holder and spin for 5-7 minutes with a velocity of 8,000 revs, per minute. 

 Read off the relative length of the column of corpuscles. As the glass 

 walls of the tubes are thick, it is advisable to aid the eye by looking along 

 a glass plate held at right angles to the tube. The tube^^have a bore of one 

 square millimeter and are divided into 100 equal parts. The reading multi- 

 plied by 2 will give the volume of corpuscles in 100 parts of blood. The 

 function of the Miiller's fluid is to retard clotting and to fix the red corpuscles 

 in their natural size. 



69. To Demonstrate the Effect of the Tension of COo on the /)H of a 

 Solution of Bicarbonate. 



Put 5 c.c. of a 0-25 per cent, solution of NaHCOa in each of three tall 

 sto})pered cylinders. To each add 2 drops of neutral red. Fill (a) with air 

 expired after a deep inspiration, (6) with alveolar air ( Experiment 70 (6) ) and (c) 

 with COj; from a generator or cylinder. Stopper and shake. Note colours. 

 Remove the COg in (c) by repeated changes of atmospheric air. Note that 

 the colour goes back from crimson through the red of (6) to the orange of 

 (a) or even to the yellow seen before any CO2 was added. 



70. Determination of the Alkali Reserve of Blood. 



(a) An approximate method. (Rieger.) Principle. Erythrocytes are 

 easily damaged by acid. This will lead to agglutination and haemolysis on 

 the addition of acid as soon as the reserve of base has been used up. 



Method. Ten test tubes (8 in. X 1 in. or thereabout) cleansed thoroughly and 

 dried are set in a rack. The first or stock tube is charged with 9 c.c. of a 

 0-85 per cent, solution of NaCl (pure salt in distilled water) and 1 c.c. of 

 whole b'.ood (oxalated with 0-2 per cent, pure sodium oxalate). Mix thoroughly 

 by drawing up into the pipette several times, keeping the tip of the pipette 

 always below the surface of the liquid. 



One cubic centimetre of the diluted blood is placed in the bottom of each 

 tube, avoiding the sides, and then, starting on the left, N/lOOHCl is added 

 from a graduated pipette. The first is given 0-75 c.c. acid, the next 0-8 and 

 so on, increasing the amount by 0-05 c.c. with each tube, the last tube thus 

 receiving 1-20 c.c. In about an hour examine the tubes. Those on the left 

 should show no haemolysis and the corpuscles should be settled in a sharply 

 defined clump in the centre of the foot of the tube. The tube on the right 

 may show haemolysis and have corpuscles scattered over the bottom in an 

 irregular manner, giving a speckled appearance. The tube with the greatest 

 amount of acid which shows no haemolysis or scattering of corpuscles gives 

 an indication of the alkali reserve of the blood. 



