THEORIES AND PROBLEMS OF CANCER 117 



meaning is somewhat obscure but from the context he appears 

 to imply that as some tumours are more malignant than others, 

 the method followed had the effect of selecting the rapidly 

 growing tumours from among other tumours, because the less 

 rapidly growing tumours could not be successfully perpetuated 

 by the method used. The selection he suggests is that of 

 different kinds of primary growths and not of variations among 

 the cells of the same growth. He refers at some length to 

 variations among cancer cells but his remarks appear to apply 

 only to morphological characters. The mode of selection he 

 suggests might apply in a few particular points with regard 

 to some experiments. It is difficult to see how it can apply 

 to most of the experiments referred to here, which appear to 

 be adequately explained by the selection of variations in poten- 

 tialities occurring among the cells of the tumours and the 

 transmission of these variations in successive generations 

 of cells. 



There are records of other observations which I think throw 

 some further light upon the difference between the behaviour 

 of transplanted tumours and that of primary growths from 

 which they are derived. These refer to the changes in the 

 histological characters of the growths from carcinoma to 

 sarcoma and vice versa and from a structure similar to that 

 of a primary cancer to that of a benign tumour. Considerable 

 interest was aroused in 1905 by the discovery in Ehrlich's 

 laboratory that in the tenth generation of transplantations of 

 a carcinoma in mice the characters of the tumour had altered 

 to a mixed sarcoma and carcinoma. In the thirteenth generation 

 this became a large spindle-celled sarcoma. 1 A permanent 

 mixed tumour was also produced from the material of four 

 different strains all of which had originally been carcinomata. 



The surprise aroused by these observations, however, was 

 somewhat uncalled for, as Loeb 2 had some years previously 

 recorded the change of a spindle-celled sarcoma occurring in 

 a rat to an endothelioma, a myxoma, alveolar sarcoma and 

 other forms of tumour upon transplantation to other rats. 

 Apolant 3 claims to have followed the microscopical changes 

 in the development from carcinoma to sarcoma and describes 



1 Ehrlich, Arb. a. d. k. Inst. f. exp. Therap. zu Frankfurt a/M., Jena, 1905, i. 77, 



1 Journ. Med. Research, Boston, vi. 28, 1901. 



3 Arb. a. d. k. Inst.f. exp. Therap. zu Frankfurt a/M., Jena, 1906, ii. 48. 



