218 



Colchicine 



trol animals demonstrate that it does not, for it can be seen that be- 

 tween the thirtieth and thirty-fifth hours after the hormone injection 

 the mitotic index rises sharply. If colchicine had been injected at 

 the thirty-first hour, a mitotic increase from 2.92 to 108.60 would have 

 been observed, and this could not be explained by the theory of meta- 

 phase arrest. This increase is, however, not only the result of mitotic 



X 35 mitotic index 



^C'2 



CALCULATED DURATION OF 



MITOSES = A = '^-^ 



x30 



x25 . 



x20 



X 15 . 



x lO - 



x5 - 



X I 



hours : I 



Fig. 9.2 — Progressive increase of the numbers of mitoses, in repeated biopsies from 

 the rabbit's uterus, after stimulation by chorionic gonadotropins and injection of col- 

 chicine. Calculated duration of mitoses on the assumption that colchicine does noth- 

 ing more than arrest them at metaphase. (From original data of A. P. Dustin, 1943 ) 



stasis, but also of the progressive action of testosterone, demon- 

 strated by the fact that in untreated animals the mitotic count rises 

 about threefold. Therefore, colchicine alone has increased the mitoses 

 only from about 10 (2.92 X 3) to 108.60 within 4 hours, which means 

 that the average mitotic duration nuist be about 25 minutes or less. 

 This agrees with knowledge of mitotic duration in mammals. 



Such an example demonstrates the intricacies of quantitative 



