230 THE CYCLE OF CELL-DIVISION 



alkali is correct according to the equation that is to 

 say, unless the index of diffusion of the jelly is correct 

 for the coefficient of diffusion of the cells, the latter 

 will take no notice whatever of the mitosis inducing 

 agents in their surroundings. But make diffusion 

 factors of the jelly right and the cells will then re- 

 spond immediately, and as many as 90 per cent of 

 the lymphocytes in a specimen may be made to divide. 

 Not only does the rapidity of the onset of mitosis 

 depend on the physical laws of the diffusion of sub- 

 stances into cells, but the actual stage reached in a 

 given cycle of cell-division also depends on them; for 

 the completion of the mitotic cycle occupies a certain 

 amount of time, which varies inversely with the quantity 

 of the stain absorbed by the cell, and this absorption 

 depends on the coefficient of diffusion, heat, alkali, etc. 

 The following experiment illustrates this point. A 

 jelly-film was made which induced almost completed 

 divisions in lymphocytes in ten minutes. By making 

 several films and removing them, one at a time, 

 from the 37 C. incubator at each minute, it was 

 seen that mitosis began with the staining of the 

 granules at about the seventh minute, and that death 

 occurred at about the ninth. The experiment was 

 repeated, and at the seventh minute, immediately while 

 mitosis was occurring, the slide was quickly removed 

 from the 37 C. incubator to one which maintained 32 C. 

 The sudden lowering of the temperature delayed the 

 diffusion of the stain into the cells, and the interesting 

 point is that the mitosis ceased when the diffusion of 

 the stain was suddenly arrested, and the cells died 



