296 THE MICROSCOPIST. 



the methods of examination and considerations useful in 

 diagnosis. 



The presence of too large a proportion of white corpus- 

 cles (leucocytes) in the blood constitutes what is known 

 as leucaemia, and is usually associated with morbid changes 

 in the spleen and lymphatic glands. But the relative 

 numbers of white and red corpuscles vary in different 

 persons, at different times, and in different morbid states, 

 so that great care is needed in forming an opinion. Thus 

 in anaemic and cancerous patients the proportion of white 

 corpuscles is increased. 



Prick the skin of the finger with a needle after moderate 

 compression, and place the drop of blood thus obtained on 

 a perfectly clear slide, and cover with thin glass in the 

 usual way. ]S r o more blood should be taken than is suffi- 

 cient to fill the capillary space between the slide and cover. 

 The white corpuscles in the field of the microscope should 

 then be counted, or an estimate made of the proportion 

 of white to red corpuscles. 



Several "fields" should be averaged before arriving at 

 an opinion. This is but a rough method, and for more 

 accurate determination a variety of tubes and slices have 

 been devised. The capillary apparatus of Dr. Malassez 

 is so constructed that one volume of blood diluted with 

 one hundred volumes of a ten per cent, solution of sul- 

 phate of soda, to facilitate enumeration and prevent co- 

 agulation, is placed in a capillary tube adjusted on a glass 

 slide so as to indicate a definite cubic capacity for a given 

 length, which relation is marked on the slide by the in- 

 strument-marker. Then, by means of an eye-piece mi- 

 crometer, divided into squares, the actual number of cor- 

 puscles, white and red, can be counted, and on multiplying 

 by one hundred for the dilution used, we have the figure 

 desired. Hayem and Cachet employ a slide having a 

 glass ring one-fifth of a millimeter in depth cemented on 

 it. A drop of blood diluted as above is placed in the cell 



