154 BACTERIOLOGICAL DIAGNOSIS. 
way we are looking at 50 squares; and this fact enables 
us to dispense entirely with the rulings and count over 
the whole area of the disc with great rapidity. The 
slide is placed in position and all the cells which are 
seen in the field counted and the result noted down, or, 
preferably, dictated to someone else. The slide is then 
moved on until a perfectly fresh portion of the field 
comes into view; it is advisable to go too far rather 
than not far enough. For this purpose (as for a great 
deal of blood work) a mechanical stage is a great 
advantage. In this way 2000 squares may be counted 
in a very short time; it is an advantage, however, to 
count 1000 squares, #.e, 20 fields, and then to clean the 
slide and to prepare a fresh preparation from the fluid 
which remains in the pipette and count another 20 
fields. 
The calculation is just the same as for the red cor- 
puscles, remembering that the dilution is very different. 
The average per square will of course be less than 
unity. The same formula is applicable. 
Immediately after use the pipettes must be thoroughly 
cleaned. The fluid which remains in the bulb must be 
blown out; and for this purpose, as well as for the 
subsequent washings, it is an advantage to reverse the 
position of the india-rubber tube, so that the fluid may 
be blown out through the upper part of the pipette, this 
being the wider. The whole pipette must now be filled 
with water (preferably distilled) and the water blown 
out. This process is repeated, using absolute alcohol 
and allowing it to run out of the pipette without blowing 
it. Lastly, fill the whole pipette with ether, remove 
the india-rubber tube, replace it with the tube of an 
ordinary spray (such as is used for scent fountains, 
throat sprays, &c.) and pump air through until the 
