COUNTING GRANULES 283 



ing the microscope mirror on its gimbals out of the 

 focal axis, the working 32-c.p. gas-light is changed 

 to the water-cooled ray of light from the 1-amp. 

 Nernst lamp. The image of the ruptured cell will 

 then be seen on the ground-glass screen at the back 

 of the camera, where it can be rapidly focused. 



The special precautions regarding the focusing 

 with this method have already been described, but 

 it should be remembered that in order to be able to 

 count the number of the granules in the ruptured 

 cell it is most important to obtain as perfect a nega- 

 tive (figs. 90, 91) as possible. 



If the photography has been accomplished quickly, 

 the camera may be pushed up out of the way, the 

 microscope mirror replaced, and the specimen may be 

 searched for more eosinophile leucocytes. 



To count the number of granules contained in a 

 ruptured cell, the negative must after it has been 

 developed and dried in the usual way be placed in an 

 optical lantern, and the image of the ruptured leucocyte 

 projected on to a screen which has a sheet of white 

 paper pinned in front of it. One stands close in front 

 of the screen and counts the granules, each of which 

 will now appear about the size of a shilling-piece, and 

 the image of each granule can be "ticked off" with 

 a pencil on the paper (figs. 92, 93) . It is thus impossible 

 to count any granule twice over, and an accurate 

 enumeration can be made. 



Such is the technique. By it there have been 

 counted 38,759 granules from 235 cells from 96 persons, 



