ABNORMAL GROWTH. TUMOURS 263 



Tumours which are the Result oe Escape from 

 Unnatural Arrest. 



1. Where the Arrest was comparatively late in appli- 

 cation. 



Let us suppose that in a certain region of a developing 

 embryo cell-differentiation from mucous tissue into fat 

 tissue was about to commence, and that several of the cells 

 were unnaturally arrested and remained isolated amidst the 

 multiplying evolving fat cells. On the attainment of 

 maturity the normal fat tissue in the region mentioned would 

 consist of cells naturally arrested, while in their midst would 

 be those unnaturally arrested, both as regards multiplication 

 and species-evolution. 



If now these latter cells started to multiply, their product 

 would be unexpected, for the lack of their product earlier 

 in the life of the Individual would have been made good 

 by the extra proliferation of the unarrested cells. 



The new growth would now try to fulfil the destiny 

 originally potential in the unnaturally arrested cells, but 

 would find no place for itself in the fully developed body- 

 plan ; and as a result an innocent tumour would develop 

 myxomatous or fatty in nature, or it might be exhibiting 

 both characters, according to whether the unnatural arrest 

 preceded or coincided with fat-tissue differentiation. 



If the latter was the case, the tumour would be a lipoma 

 with fat cells apparently identical to those of the surrounding 

 fatty tissue. In reality, however, the tumour cells would 

 be less highly evolved than the cells of the normal fat-tissue, 

 and presumably only after much cell-multiplication would 

 they become " equivalent " to these. At the same time 

 this multiplication would take place in a mature body 

 environment, and not in that of the developing body, as 

 ought to have occurred. 



That the tumour cells are fat cells suggests that their 

 development is controlled as regards character, and it may 

 be that the surrounding environment of normal fat tissue 

 exerts the influence. At the same time it is to be remem- 

 bered that when the unnatural arrest occurred the destiny 

 of the cells affected was already largely fulfilled. On the 



