Experimental Growth in Animals 221 



9.3 gives the results, with the percentages of dividing cells and of 

 mitotic stages in control and colchicinized aninials.'^'^ From these 

 results, it is apparent that mitotic arrest at metaphase has increased 

 in six hours the number of cell divisions by 17.63/3.32. The mitotic 

 duration, calculated as indicated in Section 9.2, is 3.32 X 6-0/17.63 = 

 1.13 = 1 hr. 8 min. It can be calculated from this result that in 

 37.7 hours (1.57 days), 100 per cent of the cells will have divided; 

 that is to say, a complete renewal of the e])ithelium will have taken 

 place. This is, of course, only statistically correct, for there must re- 

 main a certain number of stem cells so that growth may persist. 

 These cells will divide into one differentiating cell and one stem cell 

 identical to the first. A great discrepancy between results obtained 

 with radio-phosphorus on the nucleic acid turnover and the figures 

 given bv the colchicine method as used by the same authors has been 

 discovered.'^! This may throw more light on the complex problems 

 of growth in differentiating tissues. 



The skin of small rodents has been excellent testing material for 

 the study of growth as analyzed by colchicine. A very extensive series 





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Fig. 9.4— Colchicine-mitoses (black dots) in an ovarian follicle (left), ancJ in Follicular 

 cells surrounding an egg found in the uterus in the rat. (After Allen et al. ) 



of experiments has been carried on, especially by Bullotigh.-^ -^ This 

 has provided ample material for a precise analysis of growth and the 

 fundamental mechanisms of mitosis. Further reference Avill be made 

 to some of these jiapers in the section on hormonal stimulation of 

 mitosis. Diurnal variations, the action of sleep, the efiects of blood- 

 sugar level and ol injections of starch, have led to the most im- 



