A 



MITOTIC FIGURE INDUCED IN A LARGE LYMPHOCYTE. 



This illustration was obtained after the book had gone to press and does not appear in 

 the list of illustrations. It is included because it so clearly demonstrates the mitosis of the 

 lymphocyte which was unstained. The division was induced by means of bensamidine, one 

 of the several compounds containing the amidine grouping (N = C N) the presence of which 

 appears to be necessary in a substance before it can cause cell-division. This point was de- 

 termined after the book had gone to press. 



