1912.] Resistance to the Groivth of Implanted Cancer. 213 



14 days, in the hope that in this way a high degree of immunity might be 

 maintained over a long period. 



The result obtained was not encouraging, even although the strains 

 employed fell a ready prey to a resistance evoked before grafting. Taken 

 over all, the tumours grew more slowly than in the control animals, but 

 then regression was not brought about. 



The main conclusions to be drawn from the above investigations are : — 



1. Tumour parenchymata vary widely in their power of inducing resist- 

 ance. This factor must not be lost sight of in the prosecution of researches 

 in immunity to transplanted cancer. 



2. The individuality of the animal inoculated may contribute to the 

 development of resistance, although not to so marked a degree as the tumour 

 parenchyma. 



3. Simultaneous inoculation of a tumour strain which induces no resistance, 

 and a strain which induces resistance, may be followed by marked inhibition 

 of the growth of the former strain. 



4. Mice bearing progressively growing tumours can be rendered resistant 

 to re-inoculation, but the tumour first inoculated need not necessarily be 

 affected. 



5. Eepeated inoculations of tissues, such as mouse embryo skin which 

 renders animals resistant to subsequent inoculation, have not been shown 

 to have a constant effect upon the growth of established tumours. 



6. The conclusions drawn in (4) and (5) support the view previously 

 expressed that immunity to cancer is directed mainly against the stroma- 

 eliciting properties of the cancer cell. 



