262 THE EVOLUTION OF CONTINUITY 



a main evolutionary road, there is an accompanying side- 

 evolution of cell-species for the performance of special 

 function. And these species when fixed, or fully differen- 

 tiated, represent so many arrested evolutionary lines of the 

 Individual, repeated cell-multiplication never in their case 

 ending in the restoration of sexual elements. 



It is through this fundamental interpretation of the 

 living growth-cycle that a theory of tumour formation can 

 be offered capable of embracing tumours innocent and 

 malignant. This is to the effect that the problem centres 

 in Arrest, and Release from Arrest. 



Fundamentally, Arrest may be Unnatural, or Natural. 



Unnatural Arrest is the premature arrest of cells of the 

 developing Individual, and it may occur in two forms. 

 (1) At a very early stage of development, long before tissue 

 differentiation has occurred, or the fixed cell-species of the 

 body have evolved. (2) At a later stage, when full differen- 

 tiation is about to be accomplished. It represents the 

 absolute arrest of cell multiplication, and also of given 

 lines of cell -species evolution. 



Natural Arrest, on the other hand, is the normal arrest 

 of cell multiplication which occurs when maturity is reached. 

 In one sense it is not absolute, for all through life cell- 

 multiplication goes on in most tissues to make good damage 

 or loss, and for the needs of the organism. But in the sense 

 thatj in the normal body, this multiplication is rigidly 

 controlled and limited for the preservation of the Individual's 

 size and personality, we may say that cell-multiplication 

 in contrast with that during development is arrested. At 

 the same time, naturally arrested tissues are composed of 

 fixed cell-species which as species are absolutely arrested, 

 and under normal control cannot change their characters. 

 Thus a fat cell can only become two fat cells when it 

 divides. 



Given, then, these forms of Arrest, it is obvious that 

 were the controlling or arresting influences removed different 

 results would follow — different types of growth abnormal 

 and unprovided for in the body ; all, however, would be 

 similar in the selfish " individuality " they manifested. 



