274 ON GROWTH AND OVERGROWTH 



nancy, go hand-in-hand with tumour formation of a pronounced 

 embryonic type. 



The failure to recognize the normal existence of mother cells 

 in those tissues which are prone to tumour formation is very 

 obvious in reading over Cohnheim's chapter upon tumours and 

 in following the course of the argument which led him to conclude 

 that tumours arise from latent superfluous embryonal tissue 

 lying either within a tissue of the same nature or heterotopic. 



While we must admit the existence of such embryonal rests 

 in order to explain the development of such tumours as, for 

 example, myomata of the kidney and primary cancerous growths 

 developing in bone, the permanent existence of these mother 

 cells as the normal constituent of the tissues throughout life is 

 wholly adequate to explain most benign and malignant tumours. 

 To this larger conception of what is " embryonal tissue " we 

 must, I think, inevitably come, and with Senn and others we must 

 regard tumours as products of tissue proliferation of embryonic 

 cells of either congenital or post-natal origin, even though we at 

 present continue unable to state definitely what it is that im- 

 mediately induces these cells to undertake excessive growth. 

 Granting this, that in tumours we have aberrant tissue growth 

 and that that tissue growth is due to certain cells assuming 

 excessive proliferative properties wholly outside the needs of 

 the economy, then such proliferating cells are to be considered 

 as being derived : 



1. From embryonic " cell rests " which have for a shorter or 

 longer period remained latent in one or other tissue and then 

 have taken upon themselves a rapid proliferation leading to 

 tumour formation. 



2. From the mother cells of a tissue which, remaining un- 

 differentiated, but capable of active proliferation throughout 

 life, now assume excessive proliferative powers, their daughter 

 cells retaining to a greater or less extent the characters and 

 the properties of the mother cells. 



3. From differentiated cells which reverting to a simpler, 

 more embryonic type, with this reversion gain the capacity for 

 active and excessive proliferation. 



Possibly I may add that the tendency to the development 

 of glandular cancer in later life bears some relationship to the 

 reversion and degeneration of gland cells at this period. As the 



