ESTIMATION OF THE RED CORPUSCLES 239 



poured out into a watch-glass or other suitable vessel, so as 

 to avoid any possibility of allowing some blood to escape into 

 the stock bottle, and invalidating a subsequent observation. 

 Suck the diluting fluid slowly into the pipette until it reaches 

 the single mark above the bulb; rotate the pipette between 

 the finger and thumb as you do so. 



Now remove the pipette from the diluting fluid, place the 

 tip of the finger over the aperture of the pipette (Fig. 46, S), 

 and proceed to mix the contents by rotating the pipette and 

 by turning it over and over. 



If the examination is to be made at a distance, remove the 

 indiarubber tube and stretch an indiarubber band over it, so 

 as to close both apertures of the pipette. It is advisable to 

 make the examination in a few hours, otherwise considerable 

 errors may creep in. 



3. Preparation of the Specimen. The slide which is sup- 

 plied with the instrument consists of a thick and perfectly 

 flat slip of glass (Fig. 46, o), on which is cemented a glass 

 square having a round hole in its centre (W). In the centre 

 of the hole thus left there is a circular disc of glass (5); this 

 inner disc is made of glass which is exactly 7*0 millimetre 

 thinner than that of which the outer glass is constructed. 

 When the whole cell is covered with a perfectly flat cover- 

 glass (D) there will, therefore, be a space exactly T^ milli- 

 metre deep between the lower surface of this cover-glass and 

 the upper surface of the central disc ; this space is to be filled 

 with the diluted blood. 



Slide and cover-glass are to be wiped clean with a soft 

 handkerchief moistened with water (not alcohol or xylol, 

 which may spoil the former), and then thoroughly dried; 

 there must not be the minutest particle of dust on any part 

 of the surface. 



The slide and cover-glass being ready, mix the contents of 

 the pipette as you did before (this must always be done 

 immediately before making the specimen, no matter how 

 carefully it had been done a short time previously), and blow 

 out about half of the fluid in the bulb; this is to wash the 

 diluting fluid out of the lower part of the stem. Now blow 

 very gently down the indiarubber tube so as to) expel a small 

 drop of fluid, which must be allowed to flow on to the raised 

 portion of the central circular disc of the counting chamber. 



