CONDITIONS FAVOURING OVERGROWTH 297 



functional cells, according to the extent in the alteration of their 

 relationships and the extent of the stimulus. Under one order 

 of conditions, inertia and heredity may lead the new cells to 

 assume specific characters very closely approximating those of 

 the parent cells, and the more the cells are of specific functional 

 type the slower will be the growth ; under another, the departure 

 from type may be so extensive that it is difficult to determine 

 from the individual cells the tissue in which they originated. 



Theory of Continuous Tumour Growth 



But even at this point we have not explained tumour forma- 

 tion. We have but reached the stage met with in infective 

 granulomata in which destroy or inhibit the toxic cause of the 

 cell overgrowth and that overgrowth ceases. We have still to 

 account for the continued automatic growth of tumours proper. 

 For such, it seems to me, there are two possible explanations. 

 Of these the first and most obvious is that the modified relation- 

 ship of the parts, or the stimulus which originated the growths 

 in the first place, continues persistently in action. In those 

 cases in which, apparently, modified relationships of the cells 

 to each other are sufficient to act as the primary cause of growth, 

 it is not, I think, possible to conceive the continuance of the 

 same initial disturbance throughout the life of the tumour ; the 

 very growth and massing together of the cells must remove the 

 old and introduce a new series of relationships ; we cannot, for 

 example, apply this idea of altered environment alone to explain 

 the production of metastatic growths. It is not merely the 

 outward relationships of the cells, but something in their con- 

 stitution that can alone explain this active proliferation of cells 

 in regions wholly away from their primary seat of growths, in 

 regions where they are exposed to totally new conditions. 



It is, however, quite possible to conceive the continued 

 existence of microbic parasites within the new growth or within 

 the cells of that growth, the products of which by irritating the 

 cells and modifying their functions would continually stimulate 

 the cells to multiply along the fines already laid down. It is 

 possible to conceive these cells and parasites being conveyed to 

 distant parts by the blood or the lymph stream, and when the 

 cells come to rest the associated or symbiotic parasites still by 



