Mechanism of Colchicine-Mitosis 395 



ij.i-y. Materials and inelhods. W^hile ihe problems ot colchicine 

 technique have been reviewed in C:hapter IC), it is necessary to say 

 something more about this subject in introducing a chapter on 

 s])iiidk- poisons. The fundamental processes of mitosis are very similar 

 in all nucleated cells, but it would be an error to think about cell divi- 

 \ ision as an identical phenomenon in all nature from the unicellulars 

 to higher plants and animals. Though the changes brought about 

 by exposure to colchicine are nearly identical, it has been pointed out 

 in previous chapters that Amoeba reacts only when the alkaloid is 

 injected with a micropipette into the cytoplasm, that in plant cells, 

 chromosome division proceeds for a long time in the absence of any 

 spindle, and that in animals the hormones and other influences 

 regulating cellular nudtiplication interfere with the action of colchi- 

 cine (cf. Chapters 7, 8, and 9) . 



Spindle poisons have been studied by a small group of research 

 workers, and each laboratory has used the celhdar material which 

 appeared the most convenient. It would l)e unwise to compare un- 

 critically results obtained on Allium root tips or on sea-urchin eggs 

 with those observed in fibroblast cultures or in mammals injected 

 with colchicine, or to comjiarc colchicine and spindle-poison effects 

 in normal and neoplastic cells, in embryos or in adults, in slow-grow- 

 ing cells or in tissues stimulated to cellular multiplication by the 

 action ot hormones — both in plants and animals. These facts may 

 seem e\ident from previous chapters. The great mass of data that 

 has accunuilated for twenty years about spindle poisons can only be 

 discussed with catition. It is clear that the time is not yet ripe for a 

 single theory covering all types of cells. This important point should 

 be kept in mind when, in the next pages, different and apparently 

 conflicting theories are considered. The only firm ground is that of 

 the experimental facts, and this alone provides a varied and interest- 

 ing insight into the action of spindle poisons. 



17.1-4: The problem. The jnnpose of this chapter can now be 

 defined more clearly. The fundamental problem is that of spindle 

 inactivation by colchicine, a highly specific property of a complex 

 molecide. Other spindle poisons will be considered as far as they 

 help to understand colchicine, and also the modifications of the 

 fibrous properties of the spindle, as evidenced by its structine and by 

 sLibmicroscopic evidence (polari/ed light) ^••'^- ''i (Chapter 8) . 



The following jjoints will be considered: 



(1) Like most biological activities, spindle formation and modifi- 

 cations during mitosis may be under the control of enzymes. Most 

 work on the effects of colchicine on enzyme systems does not bring 

 much tiseful evidence, fjut should be pmsued. Some of the latest 

 theories, discussed in Subsections 17.5-2 and -4, point to enzymes as 

 the targets inhibited l)y colchicine. 



