Mechanism of Colch'icine-Mitosis 



393 



of colchicine. These have been analyzed at length in Chapters 2, 3, 

 and 4, and only a short summary is necessary at this point. Colchi- 

 cine is a mitotic poison; that is to say, it belongs to the vast and 

 rajiidly increasing group of substances which act spccificallv on divid- 

 ing cells. In Chapter 7 many other actions of the alkaloid on "rest- 

 ing" (intermitotic) cells were mentioned, but these are limited to 



Fig. 17.1 — Root tips of Vicia faba treated for three hours by a 1 per cent solution of 



chloral hydrate and replaced for 24 hours in water. Pseudo-metaphases and pseudo- 



anaphases. (After van Regemoorter,""' Fig. 1) 



some specialized tissues and to some groups of animals. Effects on 

 cell-shape, apart from mitosis, have also been recorded in Chapter 4. 

 These arc most interesting for a proper understanding of the c-mitotic 

 effect, but are mainly side-effects, usually brought about with strong 

 concentrations of the alkaloid. 



On the contrary, the sjjindle action is remarkably sjiecific, and 

 solutions of colchicine diluted to one part in one billion, may still 

 exhibit spindle poisoning: colchicine has Jiiij^h ncthnly. This is ex- 

 pressed as the inverse of the activity threshold. Colchicine is also of 

 great efjiciency; that is to say, it acts over a wide range of concentra- 



