282 THE DIVISION OF LEUCOCYTES 



on" and focused, and the cell is brought into the 

 centre of the field. Watching it through the eye- 

 piece, keeping one hand on the fine adjustment, 

 the cover-glass, which of course is resting on the 

 jelly-film, is gently struck (tapped) with a glass rod 

 held in the other hand. At each tap the cells are 

 seen to be jerked out of the field, but, provided the 

 taps are not too forcible, the eosinophile cell can 

 easily be followed by using the mechanical stage. 

 It is usually necessary to strike the cover-glass two 

 or three times, and generally at the third blow the 

 eosinophile is seen to totter and then burst, scattering 

 its stained granules about on the surface of the jelly 

 in the field of the microscope. This is a trick, of 

 course, which was devised by one of us (J. W. C.), 

 and with a little practice rupture can nearly always 

 be assured. 



When a cell ruptures on this jelly which contains 

 salts its nucleus loses its stain instantly, but at the 

 room temperature the granules do not usually become 

 achromatic for some little time. On the other hand, 

 in some instances they may become unstained in a 

 few moments, and for this reason, in order to secure 

 the photographic negative, speed is now required. 

 The ruptured cell is placed in the centre of the field 

 'with the mechanical stage; the working eye-piece is 

 removed from the microscope, the camera is allowed 

 to slide down the wooden slide, and its projecting 

 eye-piece, which is already attached to it by means of 

 a flexible velvet collar, is inserted into the draw-tube 

 of the microscope. By the simple movement of swing- 



