n8 SCIENCE PROGRESS 



the cells of the sarcoma as being derived from those of the 

 stroma and not from the carcinomatous cells. Subsequently 

 Bashford 1 made similar claims with regard to a similar change 

 from carcinoma to sarcoma with another strain of tumours. 



It is not made at all clear by these observers, however, 

 that the carcinomatous cells themselves do not take on the 

 characters of sarcoma, so the real point of their claim — 

 that the sarcoma develops from the stroma and not from the 

 carcinoma cells — remains very doubtful. Apolant 2 transformed 

 a carcinoma into a benign adenoma by transplanting it into 

 immunised mice. 



In considering these observations, one realises that besides 

 the general effect upon the health of the animal and the other 

 points of difference already referred to between the trans- 

 planted tumours and primary cancer, there appears to be a 

 difference in the general history of the succeeding generations 

 of cells which form the growths. There is, I think, no record 

 of a primary carcinoma changing into a sarcoma or vice versa, 

 yet such changes in transplanted tumours were noted directly 

 they were brought under systematic observation. 



It is quite clear that the conditions obtaining in a primary 

 cancer must be very different, in so far as the cells forming 

 them are concerned, from the conditions to which the cells 

 of the graft are subjected. The cells of the primary growth 

 are subjected to a minimum of selection by the environment, 

 as they or their immediate ancestors have arisen in the 

 identical environment in which they continue. Moreover, 

 they must act less as foreign bodies towards the surround- 

 ing tissues from which they arose than do cells introduced 

 from outside and so do not cause that inflammatory reaction 

 which is so marked a feature in tumours growing from grafts. 

 These considerations suggest an explanation of the invasive 

 nature of the primary growth as compared with the non- 

 invasiveness ol those arising from grafts and for the rarity 

 or total absence of true metastases in mice bearing tumours 

 produced by inoculation. The more or less stringent selection 

 of those cells possessing high resistance to a change of en- 

 vironment which is involved in the transference to new hosts 

 is probably also sufficient to account for the other differences. 



1 Berl. klin. Wohnschr. 1907, xliv. 1238. 



2 Miinchen Med. Wohnschr. 1907, liv. 1720. 



