152 BACTERIOLOGICAL DIAGNOSIS. 
ESTIMATION OF THE NUMBER OF 
LEUCOCYTES. 
All the steps are similar to those just described at 
full length, except that a different diluting fluid is used. 
The diluting fluid is one which destroys (‘‘lakes’’) 
the red corpuscles, but does not injure the leucocytes. 
It consists of a +3 or *5 solution of acetic acid (glacial) 
in water; it is better to add a small quantity of methyl 
violet or gentian violet, so that the leucocytes are 
stained and thereby rendered more prominent. This 
solution is best prepared fresh or at any rate kept in 
a well stoppered bottle. 
The pipette is distinguished from that used for the 
red corpuscles by its having the number 11 above 
the bulb. This indicates that if blood be sucked up 
to the mark 1 below the bulb, and diluting fluid up to 
the transverse mark above the bulb, the dilution will be 
1 in 10, and so on. 
The blood should be sucked up to the mark 1 if a 
great excess of leucocytes is not expected. If the case 
is one of leucocytosis a greater dilution is better, whilst 
if there is a great excess of leucocytes (such as occurs 
in severe leucocythemia) it is best to use the red 
corpuscles pipette with a dilution of 1 in 100, but 
employing the acetic acid diluting fluid. 
In counting the squares a different method has to be 
employed, as a far greater number of squares must be 
counted. Either you may count al/ the squares on the 
slide and then make a fresh preparation and count all 
the squares on it; or you may adopt the following 
method, which is much quicker and, therefore, since it 
