1910.] Resistance to Implantation of Malignant New Growths. 305 



the sixth and ninth day an active immunity which leads to the rapid 

 dostrnction of any mouse tumour cells subsequently introduced. Further, it 

 can be inferred that the production of this active immunity contributes to 

 terminating the transitory growth of mouse cancer-cells in rats. The cessation 

 of their growth is due largely to active immunity concomitantly induced, and 

 to other influences directly injurious to them. The immunity induced in the 

 rat against mouse cancer is very different from the active resistance of a 

 mouse to inoculation of tumour of its own species, for, as demonstrated in 

 1908, mouse tumour cells can live and divide for eight to ten days in a 

 resistant mouse, but they are incapable of eliciting the stroma reaction 

 necessary for their establishment as a fresh tumour (4). 



It has been possible to demonstrate the essential difference between these 

 two types of immunity in another manner. Up to the present it has been 

 found possible to render an animal resistant to tumours of its own species, 

 only by previous inoculation of living tissues also of its own species. It is 

 shown in another communication that if mouse tumour be disintegrated by 

 pounding in a mortar cooled in salt and ice, and then be inoculated into mice, 

 it does not give rise to the development of tumours, neither does it produce 

 any immunity against mouse tumours ; on the contrary, hypersensitiveness 

 may result (13). Eats inoculated with a dose of 0"25 c.c. of mouse tumour 

 ground up in this way have then been tested by introducing " early stages " of 

 a mouse tumour. It has been found that disintegrated mouse tumour does 

 render rats actively immune against mouse tumours. The fundamental 

 distinction between the behaviour of disintegrated mouse tumour in mice and 

 rats respectively, demonstrates that the immunity induced in the rats is 

 directed not against mouse cancer qud cancer, but against mouse cancer qua 

 mouse tissue, and it is exactly analogous to the anti-bodies obtained by 

 inoculation of heterologous tissues, in the production of precipitins, hemoly- 

 sins, and cytotoxins. Indeed, corresponding reactions have been obtained 

 in vitro by means of disintegrated tumour tissue inoculated into strange 

 species (9) ; whereas the true reactions of induced resistance to cancer are 

 only obtained in vivo by inoculation of living tumour, or tissue of the same 

 species. 



In confirmation of previous results, animals already bearing rapidly growing 

 tumours can be re-inoculated successfully, and conclusions based upon 

 experimental conditions permitting of the reproduction of the features of 

 dissemination, are more worthy of consideration than conclusions based upon 

 experimental conditions which exclude such reproduction. 



The presence of an experimental tumour is compatible with the existence 

 of active resistance to re-inoculation. 



VOL. LXXXII. — n. 2 B 



