ADVANCED EXPERIMENTAL PHYSIOLOGY 147 



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 I 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 haemo- 

 globin, the worth of the corpuscle in haemoglobin is obtained. 



% of Hb 



^ - = " worth of corpuscles. 

 No. 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 



FIG. 141. The Thoma-Zeiss haBmacytometer. 



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. 



In place of the mixture of glycerine and water a mixture of 

 chloroform and benzol may be used. By the addition of either 



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, 



