ABNORMAL GROWTH. TUMOURS 265 



arrest. An increase in local blood-supply might perhaps 

 sometimes account for it. Local injury or breach of con- 

 tinuity from various causes, physical or bacterial, could 

 conceivably set free the cells from their unnatural arrest. 

 Another factor appears to be Age. The majority of 

 tumours generally, and a great number of innocent tumours, 

 appear when the sexual life of the Individual is drawing 

 to a close ; and it might well be that at such a time there 

 is a call for the development of any arrested potentialities, 

 or perhaps a weakening of certain inhibiting influences 

 which the normal tissues exercised over the unnaturally 

 arrested cells in previous years. Internal secretion might 

 be involved in the matter in various ways. 



2. Where the Unnatural Arrest is applied early in 

 development. 



The unnatural arrest here occurs long before tissue 

 differentiation has taken place, and release from arrest 

 produces different results. There is tumour growth, but it 

 is atypical. The supposition is (like Conheim's) that some 

 of the undifferentiated cells of the early embryo, by being 

 shut off or separated from their companions during the 

 infolding of cell strata, or in some other way, find them- 

 selves in unnatural or uncongenial surroundings, and become 

 arrested. They are not wanted in their locality, and they 

 miss the growth-regulating and exciting impulses which 

 they would receive if normally situated. Environment is 

 hostile, and they assume, as it were, the characters of rest- 

 ing spores, awaiting better conditions for their further 

 development. 



The embryo so affected develops, and in time the organism 

 reaches maturity with its various somatic tissues apparently 

 normal in every respect ; yet in a certain one there lies 

 unnaturally arrested or quiescent a little group of early 

 embryonic cells. The body has developed without their 

 assistance, they perform no function, and are not really 

 part of the body except in that they are continuous with 

 it. If these cells escape from arrest when the body is mature 

 or begins to decline, they proceed to multiply actively. 



But the product of their division is not typical of any 



