8 METHODS OF EXAMINATION 



the remaining diluted blood, with pure water, drawing in water 

 and expelling it several times, then with alcohol, then with ether, 

 finally forcing air through until it is thoroughly dry. When the 

 pipette is dry the glass bead will roll about freely in the bulb with- 

 out adhering to any part. An aspirating bulb will be found time 

 saving in cleaning the pipette. To draw fluid into the pipette the 

 rubber tube may be attached or the aspirating bulb may be com- 

 pressed and the thumb placed over the valve. Care must he 

 taken not to allow the aspirator to become moistened dining 

 cleaning as the last step is to force dry air through the pipette. 

 Even when care is taken to clean the pipette well it will be found 

 necessary at more or less long intervals to fill with strong nitric 

 acid and let it act for several minutes. All trace of the acid must 

 lie removed by drawing water through the pipette several times, 

 following the water with alcohol, ether and dry air as ordinarily. 



COUNTING THE LEUCOCTYES 



If the counting chamber with the Zappert-Ewing ruling is used 

 the leucocytes may be counted in the same preparation as the 

 red corpuscles. The leucocytes in the entire ruled space, nine 

 sq. mm., are counted. The leucocytes are readily distinguished 

 as they have a bluish tinge in contrast to the straw color of the 1 

 red corpuscles. A dilution of 1:100 is more accurate when the 

 leucocytes are to be counted. Repeat the count with a second 

 drop as with the red corpuscles. 



Computation. As with the red corpuscles divide the number 

 of leucocytes counted by the volume of blood counted (.9 cnnn.), 

 and this by the dilution. The count should be repeated with a 

 second drop. The formula for leucocytes counted with a dilution 

 of 1:100 is: 



No. of leucocytes counted x 10 x 100 



= No. of leucocytes per cmm. 



When the counting chamber having only the central square 

 millimeter ruled is used, a pipette giving a dilution of 1 :1() should 

 lie used. As it costs more to get the two pipettes and is less con- 

 venient to use it is recommended to get the counting chamber 

 with the Zappert-Ewing ruling. 



With the special pipette for leucocytes it is necessary to have 



