1906.] Resistance of Mice to the Growth of Cancer. 169 



natural resistance of the mice become of subsidiary importance. On the 

 contrary, they are of great practical importance when the energy of growth is 

 low, and in the primary transplantations of sporadic tumours. As we have 

 shown, the growth of a sporadic tumour is probably to be regarded as 

 heterogeneous. Growth is proceeding rapidly in one part, and slowly or 

 actually ceasing in another. When a sporadic tumour is transplanted into a 

 large number of mice, according to our procedure, it is subdivided into 

 minute fragments, and not made into a general emulsion. Each fragment is 

 separately emulsified before transplantation, and the result of transplantation 

 is that the tumour is distributed over a large number of animals. Success, as 

 a rule, follows only in a small proportion of the inoculations, and it appears 

 probable that it is determined by the segregation of groups of cells of higher 

 energy of growth in mice whose resistance to inoculation is below the 

 average. The energy of growth of the tumour cells and the resistance of the 

 mice together contribute to the positive result. In this way the cells most 

 likely to continue to grow are separated and, by the repetition of the process, 

 a tumour is propagated by transplantation from one series of mice to another. 

 We may illustrate this by a summary of the transplantation of some sporadic 

 tumours. 



We have found that malignant new growths are encountered in mice of all 

 ages taken at random in a proportion of one tumour in 3500 animals. The 

 final results of transplanting 32 spontaneous tumours of the mamma show 

 that 2278 of the mice inoculated survived a sufficient time* to permit of a 

 final estimation, and 72 tumours have developed, i.e., one inoculation in 31*1 

 is successful, or 3'2 per cent. The conditions for successful transplantation 

 are at least 100 times more frequent in mice than spontaneous tumours. 



Fifteen out of 32 sporadic tumours transplanted gave negative results on 

 1073 inoculations. Many of these tumours were apparently very rapid in 

 their rate of growth in the animal spontaneously affected, and extensive 

 metastasis was present in the lungs after death. 



Ehrlich records similar results on primary transplantation of 94 spontaneous 

 tumours : 1504 inoculations were made and 41 tumours were obtained in the 

 inoculated animals (2*8 per cent.). The percentage of success (8*2 per cent.) 

 of the primary transplantation of the tumours (14 in number) which gave 

 positive results at all, was much higher than in our experiments. Apparently 

 our method of primary transplantation by small grafts in a large number of 

 young animals, gives success with tumours which would be completely 



* The results of the primary transplantation of sporadic tumours have been calculated 

 on the number of mice surviving three weeks later. 



O 2 



