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, i.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 



