— 174— 



Filter, and tlie solution will ])e ready for iisp. The 

 wliite 1)l<Mi(l cells are stained violet, and may thus be 

 counted with tlie red. 



The diluting lluid contained in the capillary tube is 

 then blown out, and a small drop of tln' diluted blood is 

 placed on the centre of the small glass disc. This small 

 disc is surrounded l\v a ring of glass,.cemented to the slide. 

 The glass ring is 0.1 m. ni. thicker than the glass disc. 

 When this small moist chamber is covered with a thick 

 cover glass, we have a layer of blood 0.1 m. ni. deep be- 

 tween tlu! disc and the cover glass. On the u})per surface 

 of the small glass disc (on which the droj) of diluted l)lood 

 was placed) there are nnirked ofif 400 small squares. The 

 sides of the small squares are ^V of i tn. m. long. It will 

 be seen that the layer of blood over each of tlie squares 

 w'ould have a cubical contents of — 



The hsemacytometer slide is now placed on the stage of 

 the microscope, where it should remain undisturbed for 

 several minutes before counting. The red blood cells in 

 25 to 50 squares are then counted. To ascertain the num- 

 ber of red cells in a cubic millimeter the following formula 

 may be useful : — 



