BLOOD. 2 I 7 



microscope is provided with a mechanical stage, but even without 

 this arrangement, if the observer is careful to see that the leuco- 

 cytes at the extreme boundary of one field move to the opposite 

 boundary when the position of the slide is changed, the device 

 may be very satisfactorily employed. The leucocytes should be 

 counted in 36 of the diaphragm-fields in duplicate specimens and 

 the calculation made in the same manner as explained above. 



If the leucocytes are counted in a separate specimen of blood 

 ordinarily the diluting fluid is 0.3-0.5 per cent acetic acid, a fluid 

 in which the leucocytes alone remain visible. Under these conditions 

 the dilution is customarily made in the pipette having n as the 

 final graduation. The capillary portion is of larger caliber and 

 so requires a greater amount of blood to fill it to the 0.5 or i 

 mark than is required in the use of the other form of pipette. In 

 counting the leucocytes according to this method it is customary 

 to draw blood into the pipette up to the i mark and immediately 

 fill the remaining portion of the apparatus to the n graduation 

 with the 0.3-0.5 per cent acetic acid. It then remains to count the 

 number of leucocytes in the whole central ruled portion of 400 

 squares. This should be done in duplicate samples and the calcula- 

 tion made as follows : 



Number of leucocytes in Q Number of leucocytes per 



o XN 4>OOO /\IO ~^~ oOO sss , . .... 



800 squares. cubic millimeter. 





