1906.] Resistance of Mice to the Growth of Cancer. 175 



the accompanying graphic record, through successive transplantations, without 

 the percentage of success in the direct line of propagation having fallen below 

 85 per cent. This is merely the result of an artificial selection of the tumours 

 obtained at each successive transplantation. It furnishes a special case of the 

 process already described in detail, and receives mention here because of 

 the great convenience of maximum success in inoculation for controlling the 

 experiments with which the present paper deals, and because other observers 

 have, not yet succeeded in attaining to this maximum of transplantability in 

 the case of Jensen's tumour. These results, together with the other facts 

 mentioned on a previous page, entirely do away with the statements that 

 Jensen's tumour is not virulent. We have sent our strain of Jensen's tumour 

 to Professor Uhlenhuth and Professor von Dungern. The primary results they 

 have communicated to us show that, in English mice, Professor Uhlenhuth 

 obtained 90 per cent, of success and Professor von Dungern 85 per cent. In 

 German mice the results were 90 per cent, and 50 per cent, respectively. 



The slight differences which suffice to determine the success or failure of 

 transplantation are exemplified in the following series of experiments, which 

 were devised to demonstrate the inherent fluctuations of nearly allied strains 

 of the same tumour under the same conditions at each transference. 

 Incidentally the experiments revealed the danger of comparing together 

 inoculations not strictly in the same site. 



Two strains of the same tumour were propagated simultaneously on 

 opposite sides of the body of the same mice. The strains used were chosen 

 because of moderate powers of growth, and the fluctuations they had 

 exhibited. On a series of 11 passages, it was found that the axilla was 

 invariably a more suitable site than the dorsal subcutaneous tissue : 59 mice 

 out of 286 developed tumours both back and front, 18 mice had tumours only 

 on the back, and 59 only on the front. The difference between the dorsal and 

 ventral sites is in all probability comparable to that already recorded by us 

 between the dorsal subcutaneous tissue and the peritoneal cavity. The most 

 natural explanation of the difference would seem to be that the connective 

 tissue reaction, which we have shown is specific and without which the grafts 

 cannot grow, is more readily supplied by the connective tissue of the 

 mammary region. 



In these experiments we also noted that whenever a tumour of the low 

 percentage strain developed on the back, it almost always had its fellow in the 

 axilla, the converse not holding good. 



When the greater suitability of the axilla had been established beyond all 

 possibility of doubt, the experiment was continued through five successive 

 passages in the right and left axilla. The results, as a whole, are more 



