608 SCIENCE PROGRESS 



Six tumours were removed from rats after their general 

 character of growth had been charted ; counts of N and n 

 were then made by an independent observer with the following 

 result : 



N 

 Character of growth. Ratio — . 



Very slow 300 



Slow 240 



Rather slow 204 



Rather slow at start 176 



Rapid 138 



Very rapid 82 



It will be seen that when the tumour grows more rapidly, 



the ratio of — decreases, i.e. the proportion of dividing cells 

 n 



to growing cells is larger than when the tumour is growing 

 slowly. 



Unless the gradual diminution of the ratio — with in- 



n 



creased rapidity of growth is accidental, we may see to what 



conclusions it leads. 



The normal strain of the tumour has a rate of growth such 



that it doubles its volume in about four days, and the value 



of the ratio — is approximately 100. It appears from the 

 n 



mathematical expressions obtained that the simple relation 



_? = — holds, which being interpreted expresses the fact that, 

 \i n 



since the growth of the tumour is progressive, a very much 

 bigger percentage of the dividing cells are passing over to 

 the growing stage per unit of time than obtains in the com- 

 plementary stage. The whole life cycle takes on the average 

 a time T which may be observed (vide above, four days), and 

 it can be shown, moreover,, that the time h spent by a cell 

 in the growing stage is very much larger than the time t 2 

 spent in the dividing stage — again a simple relation holds, 



viz - = — where t\ and t 2 are the respective times, and 

 t 2 n 



t x -f t 2 = T. From this it appears that in a tumour which 

 doubles its volume in four days the average time spent in 

 the process of division is about one hour. 



