6 



NUMBER OF BLOOD-CORPUSCLES. 



315 x 107 x 100 = 3,370,000 blood-corpuscles in 1 cubic millimetre. (After the 

 experiment the instruments must be carefully washed with distilled water.) 



To estimate the colourless corpuscles only, mix the blood with 10 

 parts of 0*5 per cent, solution of acetic acid, which destroys all the red 

 corpuscles (Thoma). 



Various forms of apparatus for the same purpose have been devised by Thoma, 

 Zeiss, Abbe", and Gowers. 



[The following is a description of Gowers' instrument (Fig. 3): "The 

 Hcemacytometer consists of (1.) A small pipette, which, when filled to the 

 mark on its stem, holds exactly 995 cubic millimetres. It is furnished with 

 an India-rubber tube and mouthpiece to facilitate filling and emptying. (2.) A 

 capillary tube marked to contain exactly 5 cubic millimetres, with India-rubber 

 tube for filling, &c. (3.) A small glass jar in which the dilution is made. (4.) A 

 glass stirrer for mixing the blood and solution in the glass jar. (5.) A brass stage 

 plate, carrying a glass slip, on which is a cell, of a millimetre deep. The bottom 

 of this is divided into ^a millimetre squares. Upon the top of the cell rests the 

 cover glass, which is kept in its place by the pressure of two springs proceeding 

 from the ends of the stage plate." 



The diluting solution used is a solution of sodic sulphate in distilled water, 

 S. G. 1,025, or the following sodic sulphate, 104 grains; acetic acid, 1 drachm 

 distilled water, 4 ozs. 



Fig. 3. 



Gowers' apparatus, made by Hawksley, London. A, Pipette for measuring the 

 diluting solution. B, Capillary tube for measuring the blood. C, Cell with 

 divisions on the floor, mounted on a slide, to which springs are fixed to secure 

 the cover glass. D. Vessel in which the solution is made. E, Spud for 

 mixing the blood and solution. F, Guarded spear-pointed needle. 



" 995 cubic millimetres of the solution are placed in the mixing jar ; 5 cubic 

 millimetres of blood are drawn into the capillary tube from a puncture in the 



