ESTIMATION OF THE RED CORPUSCLES l8l 



and then give the patient a single large inunction of mercury, 

 thoroughly rubbed in : Justus recommends 3 grammes (45 grains) 

 for an adult, i gramme for an infant. About twenty-four hours 

 afterwards estimate the haemoglobin again. In a positive case there 

 will be a fall of 10 to 20 per cent., and this fall may continue for 

 a day or two, and then give place to a gradual rise. 



The test should not be employed when there is marked anaemia 

 to begin with, as in these patients the blood-corpuscles seem very 

 sensitive to the mercury, even when the disease is not syphilitic. 

 With these exceptions, I believe the test to be of very great value, 

 though more importance is to be attached to a positive than to a 

 negative result. 



ESTIMATION OF THE RED CORPUSCLES 



The best apparatus for the estimation of the number of 

 corpuscles (whether red or white) is the Thoma-Zeiss hsemocyto- 

 meter. It should be provided with two pipettes, one for counting 

 the red corpuscles and one for the leucocytes. The latter is rarely 

 used and need not be procured. 



Examine the pipettes. Each has a small bulb containing 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 leucocytes may be 

 distinguished by the fact that it has the figure 1 1 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. 44, 5). In the other one the same 

 portion of the stem is graduated into three portions numbered ■^■^, 

 yij-, and 2^ij- ; 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 been drawn up to the 



