30 



Colchicine 



chromosomes acciinuilatc in pairs, "colchicine-pairs," ■''*"' in cytoplasm. 

 Their distribution then is not the usual equatorial plate arrange- 

 ment. Furthermore, an arrest at metaphase reduces the number of 

 anaphases or telophases (Fig. 2.3) thus adding to the apparent in- 

 creases in this one jjarticular stage, the c-metaphase. That is why the 

 observer is struck by a totally different mitotic pattern as he looks 

 at treated tissues throtigh the microscope. Usually tissues ha\'e a tew 

 metaphases, some anaphases, some telophases, but mostly non-dividing 

 cells. Even a meristematic tisstie in plants or a sarcoma of animals, i^ 



Early Equator. Ana- 



Prophases metaphases platss phases Telophases Reconstruction 



CONTROLS , 



COLCHICINE 

 1 in 500 millions 



1 in lOOmillions 



1 in SO millions 



1 in 40 millions 



1 in 30 millions 



Fig. 2.3 — Graphic representation of the percentages of mitotic stages in fibroblast cul- 

 tures exposed for ten hours to solutions of colchicine. With increasing concentration, the 

 percentage of metaphases with unoriented chromosomes increases. The displacement 

 to the right of the arrow, indicating the end of anaphase, demonstrates that in the most 

 concentrated solutions, nearly all mitoses remain arrested and do not proceed to telo- 

 phase. This effect is clearly related to concentration. (After Bucher, 1947) 



each noted lor cell di\isi(;n. has only a limited number oi cells show- 

 ing chromosomes at a particidar moment. It is not smprising that the 

 accumulation ot metaphases impressed one pioneering investigator 

 who described this reaction by colchicine as "an explosion of 

 mitoses. ""1 



Ultimately, exclusive of recovery, the restitution nucleus is formed 

 when the chromosomes transform-- to interphase without forming 

 the daughter nuclei. This transformation may start from an arrested 

 metaphase, thus by-passing the c-anaphase. Or, the changes-- may 

 begin after the chromosomes of each c-pair have fallen apart in the 

 (-anaphase'''' — a transition involving separate chromosomes. Some- 

 times the uncoiling begins as early as prophase. ''^ These different 

 points of origin mark three routes taken when the chromosomes "un- 

 ravel" and vmdergo transformations to interphase. If the number of 

 centromeres has doubled, a featine clearly seen at (-anaphase, then 



