1906.J Experimental Analysis of the Growth of Cancer. 221 



{cf. fig. 12) and spontaneous absorption (cf. figs. 3 and 4) supervene on a high 

 degree of transplantability and when negative results are obtained either 

 immediately, or by graduated steps, when a tumour of a series giving a high 

 percentage is transplanted. 



60 XL 41S 



40 



20 



' 700 750 800 850 DAYS 



Fig. 12. — Graphic record of propagation of a strain of Jensen's tumour which gradually 

 gave a lower and lower percentage of success till a negative result terminated 

 growth. Cf. fig. 10 and fig. 11. 



Many tumours of the mouse's mamma give negative results on trans- 

 plantation, and in this respect resemble the tumours of the other longer- 

 lived mammals. Of those, in which the primary transplantation is 

 successful, the later results often show a gradually diminishing percentage 

 of success till, finally, negative results are obtained, on transplantation. The 

 enormous proliferation obtained with Jensen's tumour is exceptional. Growths, 

 undoubtedly malignant, are not necessarily equally capable of artificial propa- 

 gation. As our experience of malignant new growths in mice widens, the 

 power which small fragments of tumour possess of establishing themselves in 

 new hosts on successful implantation is found to be rarer than might be 

 expected from the frequency of metastasis formation, to which it is closely 

 related. The factor or the factors actively responsible for the development, 

 the continued growth, and the formation of metastases of the different 

 sporadic tumours in the animals primarily affected are not equally efficacious 

 in ensuring a continuance of proliferation under the similar experimental 

 conditions of artificial propagation. We must therefore conclude that the 

 causative factors have operated with varying intensity, or that additional 

 factors are superadded in some cases. 



