AND SUBSEQUENT FIXATION 41 



the jelly into the citrated plasma, and the cells are 

 able slowly to absorb the substance as it passes into 

 the solution. 



Ordinary fixed films can now be made from the 

 rest of the mixture in the pipette. Eilms made in 

 this way, however, have not proved to be very 

 satisfactory because the dividing cells are fre- 

 quently ruptured or distorted out of recognition. 

 It may be pointed out that in making an ordinary 

 blood film by placing a drop of fresh blood on a 

 slide and spreading it out with the edge of another 

 slide, the lymphocytes, being in the resting stage 

 and spherical in shape, will always appear as cir- 

 cular cells composed of nucleus, granules, and 

 cytoplasm, no matter in what attitude they happen 

 to come to rest. But when the cells are elliptical, 

 figure-of-eight, or spindle-shaped, as they are when 

 they are dividing, the process of spreading them 

 out by force on the surface of the slide frequently 

 distorts them or even tears them asunder. The 

 delicate mitotic figures therefore may not be dis- 

 cernible, or the cells may be seen to lie in frag- 

 ments in different parts of the slide. We have 

 found it preferable to place a drop of the mixture 

 containing the dividing cells on to a cover-glass 

 and then to invert the latter on to a film (set on a 

 slide) of agar jelly containing 1*5 per cent of 

 sodium citrate and 1 per cent of sodium chloride. 

 This causes the cells to come to rest gradually and 

 evenly spread out without distortion ; and they can 

 afterwards be fixed and stained by the procedure 

 described in the last paper, 



