1906.] Resistance of Mice to the Grovjth of Cancer. 179 



inoculation, 13 of those 17 negative animals were re-inoculated in the right axilla with a 

 tumour of transplantation 63, Series M, the experiment being labelled " 64 W." Of the 

 six animals surviving after 10 days, only one presented a tumour (17 per cent.). Of 

 15 normal mice which had been similarly inoculated among the 11 surviving after 

 10 days, eight presented tumours (72 per cent.). 



Twenty-three normal mice were inoculated in the left axilla with 0*04 gramme of 

 another tumour of transplantation 62, Series ii O, the experiment being labelled " 63 T." 

 No tumours developed in the 20 animals surviving after 10 days. Thirteen days after 

 the preceding inoculation, 19 of the mice were re-inoculated in the right axilla with 

 0*03 gramme of a second tumour of transplantation 63, Series M, the experiment being 

 labelled "64 V." Of the 18 mice surviving after 10 days, five presented tumours 

 (27 per cent.). Fifteen normal mice were similarly inoculated, 12 survived, and 10 pre- 

 sented tumours after 10 days (81 per cent.). 



Differences in the size of dose of tumour probably explain the apparently 

 contradictory experience of others who have failed to produce protection in 

 this way, and of our own earlier experiments where the re-inoculation of the 

 negative animals gave a percentage almost as high as in the first instance. 

 The mass of tumour absorbed in the course of three or four negative 

 inoculations with 0*05 gramme is so great that the animals, although never 

 developing tumours, cannot be regarded as comparable with animals in our 

 earlier experiments which, inoculated the same number of times, have only 

 received relatively insignificant doses (0*01 to 0*02 gramme). 

 . Kefractoriness to various spontaneous mouse tumours is apparently 

 reciprocal. Animals which have been unsuccessfully inoculated with large 

 doses of one spontaneous tumour, whether carcinoma or sarcoma, are less 

 suitable for the transplantation of other carcinomata than are normal 

 animals. This fact receives a natural explanation in the results of experi- 

 ments detailed below on the protection conferred by the injection of normal 

 mouse blood. On the other hand, the inoculation of mice with tumour 

 material from strange species — rat, cat, dog, man — has not induced a 

 refractory state. The protection induced in mice is therefore to be interpreted, 

 not as conferred by properties common to the malignant new growths of 

 different species, but only of the same species, by the absorption of substances 

 common to the tumours and tissues of the mouse. 



(5) Protection can also be Induced by the Inoculation of Normal 

 Tissues, and Particularly by the Inoculation of Blood. 



Early in 1904 we were enabled, through the courtesy of Professor C. J. 

 Martin, P.E.S., of the Lister Institute, to study the effects of immunising 



the negative mice referred to, is a phenomenon to which we have previously drawn 

 attention (vide ' Roy. Soc. Proc.,' June, 1906). 



The tumour tissue inoculated was in what we have designated, for convenience, the 

 negative phase of growth. 



