178 Dr. Bashford, Mr. Murray, and Dr. Cramer. [Dec. 10 r 



percentage of success may, on re-inoculation, give a positive result in a 



proportion little inferior to a series of control animals. The negative result. 



in the first instance was thus due not entirely to the inoculation of refractory 



animals, but largely to the low powers of proliferation of the tumour-cells. 



introduced. 



Protocol. 



Tumour XV. Mouse with a large tumour of the fifth transplantation received from, 

 Cologne (Dr. O. Schmidt), together with 10 normal mice. 



We effected the sixth transplantation into 10 normal Cologne mice, and 147 normal 

 English mice. In the English mice, three tumours presented themselves in the 61 mice- 

 which survived 10 days after inoculation (5 per cent.). Four tumours developed in the- 

 10 Cologne mice, all having survived (40 per cent.). 



One month later one of the tumours which had developed in a Cologne mouse was 

 transplanted into 45 English mice and the three Cologne mice which alone had survived 

 out of the six negative animals in the previous experiment. All the three Cologne mice 

 developed tumours, 100 per cent., while only two tumours developed in the 20 English 

 mice surviving after 10 days. 



Eepeated re-inoculation of the negative animals with small doses of tumour 

 leads to the sifting out of a residuum which may possess a high degree of 

 resistance. As the end result of such a process of elimination by successive 

 inoculation, animals can be obtained in which, while similar control animals 

 give 70 to 80 per cent, of success, only from 10 to 12 per cent, of successful 

 inoculations are obtained. When, however, the small number of animals, 

 unsuccessfully inoculated in an experiment with sub-maximal success are 

 re-inoculated, they evince a decided increased refractoriness as compared 

 with normal animals. Some change in the animals following upon the 

 absorption of inoculation material is not an unimportant factor in the 

 development of this condition, as already suggested by Jensen. That such 

 is the case seems more than probable from the result following, when the 

 initial and subsequent inoculations are made with large doses, more than 

 0*05 gramme of tumour material. Here the refractory condition is increased 

 in a much shorter series of inoculations, so that already at the third or even 

 at the second inoculation, a diminution of 50 to 60 per cent, may be 

 observed as compared with normal animals. This result confirms Ehrlich's, 

 observations on the same subject. 



Protocol to Illustrate Increased Kesistance after a Preceding Negative 



Inoculation. 

 Nineteen normal mice were inoculated in the left axilla with 0'04 gramme of a tumour 

 of transplantation 62, Series ii C,* the experiment being labelled " 63 S." All the mice 

 survived, but two only presented tumours after 10 days. Thirteen days after this. 



* Transplantation 62, ii C, had given 19 tumours in 19 mice (100 per cent.). The low 

 percentage obtained in 63 S, and the negative result in 63 T, the experiments providing 



