142 BACTERIOLOGICAL DIAGNOSIS. 
ESTIMATION OF THE RED CORPUSCLES. 
The best apparatus for the estimation of the number 
of corpuscles (whether red or white) is the Thoma- 
Zeiss hemocytometer. It should be provided with two 
pipettes, and costs about thirty-six shillings. 
Examine the pipettes. Each has a small bulb con- 
taining a little glass ball and a stem which is graduated 
into several parts below the bulb, and has a single 
transverse graduation above it. 
The pipette intended for use in counting the leuco- 
cytes may be distinguished by the fact that it has the 
figure 11 over the single transverse graduation above 
the bulb. 
There are two sorts of pipettes used for counting the 
red corpuscles. In the one form the stem below the 
bulb is divided into ten parts, the upper one (nearest 
the bulb) being marked 1, and the middle one o'5 
(fig. 23, S). Inthe other one the same portion of the 
stem is graduated into three portions numbered ;45, 
zio, and 345; the figure mentioned first is placed 
nearest the bulb. These pipettes are used in the same 
way, and it is quite immaterial which is obtained; we 
shall describe the use of the first form. 
The rationale of the method is this:—Blood is sucked 
up to one of the divisions on the lower part of the stem, 
and then an inert diluting fluid is drawn up to the 
single mark above the bulb, and the two mixed by 
rotating the whole apparatus for a minute or two. 
This gives us a dilution of blood of definite strength, 
the exact amount of dilution depending upon the 
amount of blood which was taken. Thus, if blood had 
