TECHNIQUE 247 



methylene blue do not induce divisions like azur, 

 and yet they kill the cells by staining the chromatin 

 of the nucleolus-centrosome. Why should only the 

 latter dye cause cell-division; presumably both would 

 cause death-struggles ? Moreover, we have often killed 

 cells by prussic acid and nitro-benzol, but no division 

 occurred and nothing resembling a death-struggle. 

 Again, in connection with the experiment given in 

 this chapter in which it was ascertained that the stage 

 reached in a single act of mitosis varies directly with 

 the quantity of the chemical substance absorbed, it 

 appeared to us that if these mitotic figures induced in 

 lymphocytes were in the nature of death-struggles, 

 a cell once it had been started in its act of mitosis 

 would continue that act until it was complete. But 

 as the experiments showed, they did not do so, for 

 when the diffusion of the chemical agent was arrested 

 the mitosis ceased even in its early stages. 



These suggestions were worthy of consideration, 

 and the only way to disprove them was to continue 

 the investigations. It appeared to us reasonable to 

 suppose that other cells, besides lymphocytes, would 

 possibly respond by dividing to the chemical auxetic, 

 and we also considered it possible that other chemical 

 agents existed which would induce divisions. Lym- 

 phocytes responded in such a constant manner, and 

 always required a definite quantity of the substance 

 that we thought it possible that there might be some- 

 thing similar to it in the body which would cause their 

 proliferation. The question was, What was this sub- 

 stance and where was it contained ? Was it associated 



