126 RESPONSES OF CELLS ON THE BIOLOGICAL LEVEL 



as mitotic poisons because they have the common effect 

 of deranging of mitosis. At present our knowledge of 

 the biochemical, biophysical and biological character- 

 istics of the various known mitotic poisons is quite in- 

 sufficient for an analysis of their actions, but some hints 

 of the type of sub-groupings that may be expected are 

 available. For example, colchicine differs frommostof the 

 other mitotic poisons in that, in low concentrations, its 

 action appears to be almost entirely restricted to sup- 

 pression of spindle-formation. It is therefore probable 

 that it attacks the cell in a different way from, say, some 

 of the nitrogen mustards, with which bridge formation 

 and fragmentation are very prominent phenomena. 



OsTERGREN has shown that a very wide variety of or- 

 ganic compounds may cause stickiness (adhesion of 

 chromosomes) and suppression of spindle-formation. 

 The equitoxic concentrations of these substances are 

 roughly proportional to their oil-water partition coeffi- 

 cients, and it may be that in such cases the toxic effect 

 is produced by a mechanism similar to that discussed 

 in the chapter on narcosis. A small number of substances 

 are active as mitotic poisons in concentrations much 

 smaller than would be suggested by their oil-water par- 

 tition coefficients. This suggests that their action is a 

 specific action on the cell at some point more intimately 

 related to mitosis than is the generalised effect of organic 

 compounds which is proportional to the oil-water par- 

 tition coefficients. It does not, however, necessarily 



