88 PRACTICAL PHYSIOLOGY 



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 Hayem's 

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



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 ^Vs c.mm., 

 therefore 1 c.mm. contains 4000 times the average number found in a 

 square. The dilution of the blood was 1*100. 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 

 corpuscles in a square with the percentage of the haemoglobin, the 

 worth of the corpuscle in haemoglobin is obtained. 



J ofHb = 'worth' of corpuscles. 

 JNo. in sq. 



The average number of red corpuscles is 5,000,000 per 1 c.mm.; of 

 white, 10,000 per 1 c.mm. 1 



Specific Gravity of the Blood. A number of test-tubes are taken 

 and filled with mixtures of glycerine and water, which vary in specific 

 gravity from 1030 to 1075. A pipette is taken with the point bent 

 at a right angle. The skin is pricked behind the finger nail, and a 

 drop of blood is drawn into the pipette. The blood is blown in small 

 droplets into the middle of the solution in several of the test tubes 

 until the solution is found in which the blood neither sinks nor rises. 

 The specific gravity of this solution is determined with the hydrometer. 

 The behaviour of the droplet must be noted at the moment when it 

 enters the solution. The blood quickly alters owing to osmotic change. 

 The specific gravity of the blood is about 1060, of the plasma 1026-29. 

 The specific gravity of fragments of muscle or other tissues may be 

 determined in the same way. The method is - thus employed to 

 determine the amount of tissue-lymph in the organs. 



1 After using, clean the pipettes of these instruments. Suck water, alcohol, 

 and ether up them in turn, and let the liquids run out. Never blow down the 

 pipettes. 



