50 



MANUAL OF HISTOLOGY. 



tened capillary tube, the capacity of a given length of which has 

 been ascertained previously and marked on the slide to which 

 the tube is fixed. Thus, in his capillary tube a length of 400 mi- 

 cromillimetres represents the T? V.* P art of a cubic millimetre 

 of the mixture. The counting is performed with the aid of a 

 squared ocular micrometer, the microscope tube having been 

 previously so adjusted by the aid of a stage micrometer that 

 the side of the square shall have the value of one of the lengths 

 (400 n ' for example) marked on the slide. The result of the 



SDi I 



FIG. 21. Hayem and Nachet's apparatus for blood -counting. 



counting gives the number of corpuscles in a known quantity 

 (TW c.mm.) of the mixture, and the number in a whole cubic 

 millimetre can therefore be readily determined. 



Dr. Keyes uses a modification of the method of Hayem and 

 Nachet, making a dilution of 1 to 250, in order to render the 

 counting more easy. In Fig. 21 the pipette, A, is filled up to 

 the mark, 5 D ; it is then emptied into the glass vessel, F. The 

 pulp of the finger of the patient whose blood is to be tested 

 should be pierced with a triangular needle (glover's). Quick 



1 A micromillimetre (/*) = 



