222 



Colchicine 



portant conclusion that carbohydrate metabolism is indispensable 

 for mitosis in epidermal cells, and that it provides the energy neces- 

 sary for a cell to initiate division. Once prophase has started, no 

 further energy requirements are apparent, and mitosis proceeds as 

 if it were an all-or-none reaction.-^- -^ These experiments have also 

 shown that the mitotic increase after colchicine corresponds to a 



TABLE 9.2 

 Effect of Age on Mitotic Actimtv in the Pituitary Glands of Female Rats 



(After Hunt^^) 



Age 



(days) 



Pituitary Mitoses 

 (per sq. mm.) 



96 77.5 



148 45 



188 32 



220 15 



300 5 



normal duration of about three hours. This is very long compared 

 to that of ten minutes mentioned in Section 9.1. The difference may 

 be partly explained by the action of hormonal stimulation, which not 

 only increases the number of new cells starting to divide but also 

 apparently shortens the duration of mitosis. This will be considered 

 in a subsequent paragraph. Some other complexities of the study 

 of epidermal growth and of the action of colchicine can be under- 

 stood by the tact that the alkaloid may decrease the number of ne^v 

 mitoses,-^ and that unless observations are made within six hours 

 after the injection of the alkaloid, some arrested metaphases may 

 proceed to telophase. 



TABLE 9.3 



Dividing Cells (per cent) in the Ileal Epithelium of Male Rats 



(After Leblond and Stevens^") 



