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 haemocytometer. 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 ii 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 i, and the middle one 0-5 

 (fig. 23, S). In the other one the same portion of the 

 stem is graduated into three portions numbered T Q, 

 3-i^, and ^J n ; 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 



