380 Colchicine 



animals. Here again, temperature may play a great part, but no 

 quantitative work relating temperature to the duration of action of 

 colchicine exists. In tissue cultures, colchicine may be left to act 

 much longer, and 24 hours is often mentioned in work with bone 

 marrow. - 



This brings in another problem which we have not yet dealt 

 with: the duration of interphase. It is evident that, if colchicine were 

 acting longer than a normal interphase, no more new prophases 

 would be available and the mitotic index would cease to rise. While 

 most data on grasshoppers, i'' tissue cultures,^- and complex tissues 

 indicate that interphase is far longer than mitosis, precise information 

 is often lacking. It has been suggested that colchicine itself may pro- 

 vide a means for measuring the duration of interphase. ^'^ If new pro- 

 phases were indefinitely provided by the tissues, i.e., if interphase 

 diuation did not interfere with mitotic counts, the number of 

 arrested mitoses would increase until all the cells would be in a con- 

 dition of c-mitosis. This is never observed, and even in the fastest 

 growing tissues never many more than 50 per cent of the cells show 

 c-mitoses. This is because after a certain time no more interphasic 

 cells are ready for prophase. On the curve of the numbers of mitoses 

 in function of time, the time which elapses between the beginning 

 of mitotic arrest and the leveling of the number of mitoses is related to 

 the duration of interphase. Theoretically, under ideal conditions, it 

 is equal to interphase. ^'^ This is of interest for workers handling 

 colchicine and certainly deserves further study. In the preceding 

 chapters, enough has been said about the comi:)lexities of c-mitosis 

 to prevent conclusions to be drawn hastily. One fact remains true: 

 In colchicine experiments, the duration of the action of the alkaloid 

 should be much shorter than the interphasic duration of the cells 

 which are studied. 



Considering the great variations in mitotic duration which are 

 mentioned in the literature (from about 30 minutes to three hours 

 in the mouse) , our ignorance about the duration of interphase, the 

 difficulties of accurately counting mitoses, and the complexities of 

 colchicine's pharmacology, it is evident that quantitative conclusions 

 are only possible in a few instances. 1 he advantages of tissue cultures 

 are obvious. 



16A.4: Polyploidy 



Polyploid animals have been produced experimentally, -•■^- -^- ^ but 

 colchicine has not yet proved very effective in doubling the chromo- 

 some number. This is prol^ably only a question of technique, though 

 cellular destruction, nondivision of the centromeres, and restitution 

 during early development (Chapter 8) may be factors which prevent 



