130 



PRACTICAL PHYSIOLOGY 



The finger behind the nail is cleaned with alcohol and ether, and a 

 drop of blood is drawn by the stab of a lancet-shaped needle. The 

 finger should not be constricted by a ligature during this operation. 

 The point of the pipette is placed in the drop, and the blood is 

 aspirated as far as the mark 1. The traces of blood on the point 

 of the pipette are then removed, and the pipette is dipped into 

 Hay em's fluid. 1 



This fluid is sucked up until the diluted blood reaches the mark 101. 

 The tip of the mouth-piece is then closed by the finger, and the pipette 

 shaken. The glass bead in E mixes the blood and Hay em's fluid. 

 The bulb contains 1 part blood and 99 Hay em's fluid. 



1 f> 



FIG. 130. The Thoma-Zeiss haemaoytometer. 



Now blow gently into the mouth-piece, reject the first few drops, 

 and then place a drop upon the centre of the counting chamber. The 

 cover-slip is then placed in position, and the counting chamber is 

 placed on the stage of the microscope, and left at rest for a few 

 minutes. When the corpuscles have subsided, count the number in 

 10 squares, and take the average. Count those corpuscles which 

 happen to lie on the lines on two sides of each square only. 

 Each square covers an area of T ^ sq. mm., and has a volume of 

 Y^-Q c.mm., therefore 1 c.mm. contains 4000 times the average 

 number found in a square. The dilution of the blood was I'lOO. 

 Thus the number in a square x 4000 x 100 = number of corpuscles in 

 1 c.mm. of blood. 



In counting the white corpuscles it is best to dilute the blood with 

 1 per cent, acetic acid. This destroys the red corpuscles and brings 

 the white clearly into view. By comparing the number of the red 



1 Sodium chloride, g. 2; sodium sulphate, g.10; corrosive sublimate, g. 1; 

 water, g. 400. 



