42 J. F. Danielli 



Muggleton has found that if cells are kept for some months 

 under maintenance conditions, without growth, they show 

 marked differences from cells which are allowed to proliferate. 

 Cells which proliferate normally follow the pattern shown in 



/ ^O 



o 



o — -oCT 



normal 

 proliferation 



o dies 



behaviour after 

 long period 

 ""*-*. O -Odies without growth 



O — -Qdies 



Fig. 2. To illustrate the effect of a period 

 without growth on proliferation of amoe- 

 bae. In the upper diagram, three divisions 

 have given rise to eight identical cells. 

 After six months without growth, restora- 

 tion to growing conditions results in the 

 products shown in the lower diagram, i.e. 

 three cells are produced which die, and 

 one cell persists, equivalent to a stem cell. 



the upper part of Fig. 2, division being equational and all the 

 daughter cells apparently equivalent. But after six months 

 without growth, on restoration to normal growing conditions 

 the result shown in the lower diagram is obtained — the 

 daughter cells are not equivalent and one of the products of 

 each division dies after a relatively brief life. 



