6R THE CIRCULATING LIQUIDS OF THE BODY 



undiluted blood would contain 400,000 times the number of corpuscles 

 in one square. Suppose the average for a square is found to be 13. 

 This would correspond to 5,200,000 corpuscles hi i cub. mm. of blood. 

 Compare your result with the true number supplied by the demon- 

 strator. (2) Prick the finger to obtain a drop of blood, and repeat 

 the crunt as in (i).* 



To Count the White Corpuscles. Add to i part of blood 9 parts of 

 i per cent, acetic acid, in order to lake the coloured corpuscles and 

 render it easy to see the leucocytes. 



II. Relative Volume of Corpuscles and Plasma by Haematocrite. 

 (i) For practice, fill the two graduated glass tubes with the defibrinated 

 blood of an animal. The rubber tube with mouthpiece supplied with 

 the apparatus is to be attached to the glass tube, and the blood sucked 

 up. Press the tip of the index-finger against the pointed end, and care- 

 fully remove the rubber tube . Place the tube in the haematocrite frame , 

 blunt end outwards that is, farthest from the axis of rotation and 

 then slip the pointed end down into position against the spring. Instead 

 of the rubber tube, a special suction pipette for automatically filling 

 the graduated tubes may be employed (Daland) . Attach the haemato- 

 crite frame to the centrifuge, and rotate till the volume of sediment 



Fig. 19. Haematocrite. A, haematocrite attachment with graduated tubes; B, auto- 

 matic pipette for filling the tubes (Daland). 



(corpuscles) ceases to diminish. The graduations are best read with a 

 hand lens. The leucocytes will be seen to form a thin whitish line 

 proximal to the column of red corpuscles. 



(2) Prick the finger or the lobe of the ear, fill the tubes as in (i), and 

 centrifugalize. Everything must be done as rapidly as possible, so 

 that the blood may not clot till the separation of plasma and corpuscles 

 is completed. The centrifuge must rotate very rapidly (about 10,000 

 revolutions a minute) for two or three minutes. For clinical purposes 

 it is best to rotate the centrifuge always at the same speed for the 

 same length of time rather than to aim at reaching a constant length 

 of the column of corpuscles. In this way useful comparative results 

 can be obtained. It is well, to avoid the risk of accident, to rotate the 

 centrifuge under a guard. 



12. Electrical Conductivity of Blood. (i) Fill a small U-tube with 

 blood up to a mark. In each limb insert a platinum electrodef con- 



* If the tube has not been properly filled, blow the blood out immediately. 

 On no account permit it to clot in the capillary tube. 



t If the platinum electrodes are of good size and the resistance of the tube 

 of liquid considerable, it is not necessary to platinize them i.e., to cover them 

 by electrolysis of a solution of platiuic chloride with a layer of platinum-black. 



