272 



so as to ensure thorough mixing. After rejecting 

 the first few drops, which consist of diluting fluid 

 simply, a small drop of the mixture is blown on 

 to the counting chamber, and the coverglass 

 applied as rapidly as possible. No fluid should 

 escape into the moat or under the coverglass. 

 When Newton's rings are seen between the cover- 

 glass and side of the chamber, the former is in its 

 right, closely-applied position. 



In counting the corpuscles in each square, 

 include, of those that touch or overlap the sides, 

 only those on the left hand and top side or right 

 hand and bottom side. Count at least 1,000 cells, 

 the error is then only about two per cent. 



The number of corpuscles per mm.' 

 _ No. of corpuscles counted x dilution (100) x 4,000 



Number of squares counted. 

 The normal average values are for man 5,000,000, 

 for woman 4,500,000. 



Total Leucocyte Count 



The leucocytes may also be counted at the 

 same time as the red cells, i.e., from the pipette 

 used for the red. This method has the advantage 

 that all errors effect both counts equally, and the 

 true ratio of red to white may still be got. Now 

 for counting the leucocytes much larger fields are 

 necessary than in the case of the red, as for every 

 five hundred red cells there is only one white, so 

 that counting chambers especially ruled are often 

 sold for this purpose, but their use is unnecessary 

 and may be obviated by the following method. 



We require simply to determine the area of the whole 

 microscope field with a given eye-piece, objective and given 

 length of tube. 



