1906.] Resistance of Mice to the Growth of Cancer, 171 



A mouse which had been repeatedly inoculated unsuccessfully with Jensen's 

 tumour developed a spontaneous growth of different histological type 

 (XXXVIII) seven months later. This tumour, transplanted into 86 normal 

 animals, gave rise to 20 tumours, of which 18, after attaining a diameter of 

 5 mm. and over, disappeared spontaneously. The mouse in which this tumour 

 had developed remained protected against Jensen's and refractory to four 

 spontaneous tumours. 



The experiments are very few in number, and only tentative conclusions 

 can at present be drawn from them. 



Five spontaneous tumours were transplanted into 11 mice in all, 

 spontaneously affected with cancer. The results above recorded show that 

 transplantation does not reveal conditions exceptionally favourable for growth 

 in them, as compared with normal animals. The animal itself is only 

 exceptionally successfully inoculated. 



Bearing in mind the small number of spontaneously affected animals 

 inoculated as compared with the large numbers of normal animals, these 

 experiments show that spontaneously affected animals are not greatly more 

 susceptible to cancerous inoculation than normal animals.* Tumours which 

 do not grow in normal animals rarely grow when transferred to other parts of 

 the animal's own body, and not at all in other spontaneously affected animals. 



These facts, together with the development of a tumour in a mouse pre- 

 viously inoculated unsuccessfully with Jensen's tumour, further emphasise 

 the distinction to be drawn between the conditions of origin and the 

 conditions of growth. They also seem to render superfluous any subsidiary 

 assumption of a constitutional condition as necessary in addition to the 

 primary cancerous transformation in the development of spontaneous cancer.f 



* The results of the above experiments might, on superficial examination, appear to 

 justify the opposite conclusion to that drawn by us. The tumours of mice XXXIII and 

 XXXIV were transplanted successfully in those mice themselves in single experiments, 

 as against only three successes out of 99 attempts in normal animals in the one case, and 

 with negative results in 176 attempts in the other. Of all the sporadic tumours trans- 

 planted into other mice suffering naturally from cancer, XXXII alone grew in a single 

 experiment, giving at the same time only four successes out of 156 attempts in normal 

 mice. It would thus appear that 100 per cent, of success had been attained on three 

 separate occasions when transplantation was effected into mice naturally suffering from 

 cancer, as against very low percentages in normal mice. The results speak for a greater 

 suitability for inoculation on the part of individual mice, but not for a greater suitability 

 on the part of all mice which are naturally the victims of cancer. The conclusion as to 

 individual susceptibility is only justified if the distinction be borne in mind between 

 transplanting a tumour into the mouse in which it grew primarily, and into any mouse 

 afflicted with spontaneous cancer. The two cases are not the same, as pointed out later 

 on. The fact that a mouse is suffering naturally from cancer does not imply a greater 

 suitability for transplantation generally. — Added Feb. 8, 1907. 

 t Of., however, p. 184, Summary. 



