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HAND-BOOK OF PHYSIOLOGY. 



. screw; a brass stage plate (c) carrying a glass slide, on which is a cell 

 one-fifth of a millimetre deep, and the bottom of which is divided into 

 one-tenth millimetre squares. On the top of the cell rests the cover 

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

 from the stage plate. A standard saline solution of sodium sulphate, or 

 similar salt, of specific gravity 1025, is made, and 995 cubic millimetres 

 are measured by means of the pipette into the glass jar, and with this five 

 cubic millimetres of blood, obtained by pricking the finger with a needle, 

 and measured in the capillary pipette (B), are thoroughly mixed by the 





FIG. 79. Haemacytometer. 



glass stirring-rod. A drop of this diluted blood is then placed in the cell 

 and covered with a cover-glass, which is fixed in position by means of the 

 two lateral springs. The preparation is then examined under a micro- 

 scope with a power of about 400 diameters, and focussed until the lines 

 dividing the cell into squares are visible. 



After a short delay, the red corpuscles which have sunk to the bottom 

 of the cell, and are resting on the squares, are counted in ten squares, 

 and tlje number of white corpuscles noted. By adding together the 

 numbers counted in ten (one-tenth millimetre) squares the number of 

 corpuscles in one-cubic millimetre of blood is obtained. The average 

 number of corpuscles per each cubic millimetre of healthy blood, accord- 

 ing to Vierordt and Welcker, is 5,000,000 in adult men, and rather fewer 

 in women. 



