1906.] Experimental Analysis of the Growth of Cancer. 219 



acquisition of renewed powers of growth by the cells when proliferation 

 is becoming exhausted and may actually terminate, resulting in the 

 spontaneous absorption of tumours which had established themselves and 

 grown for a time. 



From time to time sporadic mammary tumours have occurred in the mice 

 purchased for these investigations, and with all artificial propagation has 

 been attempted. The resulting proliferation has in no case been equal to 

 that obtained with Jensen's tumour. Thus out of 20 sporadic tumours 

 transplanted the primary implantations have been negative in 9. We 

 select for detailed description the features of the proliferation resulting from 

 the propagation of two sporadic tumours (namely, VII and XIX) which 

 exemplify the behaviour of tumours capable of only limited propagation. 

 Both could be transplanted several times from animal to animal. The first 

 was transplanted into 133 mice. One tumour developed in the 12 mice 

 remaining alive after 10 days. It was transplanted after 20 days' growth 

 into 24 mice. One tumour developed in the four mice which remained 

 alive after 10 days. It grew slowly, attaining a diameter of 2 cm. after 

 184 days' growth, when it in turn was transplanted into 208 mice. Two 

 tumours developed in the 80 mice which survived the first 10 days. They 

 were transplanted after 48 and 66 days' growth respectively. ISTo tumours 

 developed in either case, and the experiment came to an end. The 

 accompanying graphic record (fig. 10) shows the contrast which obtains 



ZSO 3TO PATS 



Fig. 10.— Graphic record of propagation of a sporadic mouse tumour VII. Shows a 

 temporary rise (?) in transplantability and extinction of the tumour at the 

 fourth transplantation. 



between the artificial propagation of such a tumour and that of Jensen. 

 Another sporadic mammary tumour (XIX) was removed by operation and 

 transplanted in 85 mice. Fifteen tumours developed in 75 mice remaining 

 alive after 10 days. The accompanying graphic record (fig. 11) shows the 

 results of the transplantations. 



The ultimate fate of the propagated tumours in these two cases was the 

 same. The interest of the second case lies in the fact that the sporadic 

 tumour recurred rapidly after operation, which was rendered necessary on 



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