IMMUNITY IN TUMOR TRANSPLANTATION 405 



ence in the individuality differentials of host and transplant, which makes it 

 possible for constituents of the transplant to act as antigens in the host. Inas- 

 much as the constitution of the individuality differential depends upon the 

 genetic constitution of the organism which is the bearer of the individuality 

 differential, it may also be stated that certain genetic differences between host 

 and transplant make it possible for constituents of the latter to act as antigens 

 and to call forth processes of immunity in the host which become manifest if 

 repeated transplantations of homoiogenous tumors are made. It should then be 

 possible to demonstrate the presence of concomitant immunity in all cases in 

 which a tumor grows in an animal whose individuality differential differs to a 

 sufficient degree from its own. Experience, however, indicates that only in 

 certain cases in which a homoiogenous tumor grows in an animal bearing a 

 different individuality differential, can such a concomitant immunity be 

 shown. In other cases, the presence of immune processes becomes apparent in 

 an animal only after the successfully growing tumor has been completely ex- 

 tirpated, and in still others, only when the tumor growth comes to a standstill 

 and, in the end, the tumor retrogresses. In the latter instance, after such a 

 retrogression has taken place, immunity against a second homoiogenous trans- 

 plant can be shown to exist. It does not appear probable that in these different 

 types of immune reactions we have to deal with entirely different processes ; 

 it is much more likely that they are merely quantitative variations of the same 

 fundamental process. It is possible that when a concomitant immunity be- 

 comes manifest, the amount of immune substances produced as a result of the 

 action of the strange antigens is sufficiently great to make possible the dem- 

 onstration of these immune processes, notwithstanding the presence of a grow- 

 ing tumor, which seems to have the tendency to absorb a certain quantity of 

 immune substances and to make them innocuous. We may also assume that 

 another type of tumor may absorb so great a proportion of the immune sub- 

 stances that the immune bodies remaining free in the circulation of the host 

 are unable to prevent the growth of a second homoiogenous tumor trans- 

 planted at a time when the first one is already growing. Extirpation of the first 

 growing tumor would then make immune substances available for the attack 

 on the second tumor. In some instances, in which the individuality differentials 

 of host and transplant possess a sufficient degree of strangeness, the amount 

 of immune substance produced in response to the first homoiogenous growing 

 tumor may become so large that it gradually begins to inhibit and prevent the 

 further development of the first graft, which then ceases to grow and may 

 even retrogress. The absorption of this tumor material would still further 

 increase the strength of the immune processes, so that after retrogression of 

 this tumor the animal has become completely immune against a further trans- 

 plant of a homoiogenous tumor. But there are other cases in which, after 

 extirpation of a tumor with its antigens, the production of immune substances 

 becomes so weak that the latter are unable to prevent a subsequent successful 

 transplantation of a homoiogenous tumor. In this way it might be possible to 

 interpret the various types of immunity which can be distinguished as mani- 

 festations of the same basic process ; the differences noted would then be due 



