IMMUNITY IN TUMOR TRANSPLANTATION 425 



host against the transplant becomes effective. They applied this conception 

 also to animals which had become immune following the retrogression of 

 their tumors. In some way immunization was supposed to interfere with the 

 chemotatic attraction which tumor transplants exerted on the surrounding 

 tissues of the host. Russell and Bashford held that the mechanism of an active 

 immunity, or rather, of an active resistance against transplanted tumors, com- 

 bined with the apparent lack immune bodies in the bodyfluids of the host, 

 constituted a condition distinct from any other known kind of immunity. On 

 the other hand, natural immunity and active immunity against heterogenous 

 tumors did not depend, in their opinion, upon a lack of stroma reaction, the 

 immunity against heterogenous tumors in particular being due, rather, to the 

 cytolytic effect exerted by the injurious bodyfluids on the peripheral tumor 

 cells, a phenomena related to the formation and action of agglutinins, precipi- 

 tins and hemolysins which affect certain normal cells or proteins. Similar 

 observations to those of Russell concerning the significance of the stroma re- 

 action, were subsequently reported by Woglom in the immunity against rat 

 tumors, and by Rous in the transplantation of embryonal tissues in mice which 

 had been previously immunized against embryonal mouse tissue. According 

 to Rous and Murphy, in the transplantation of chicken sarcoma into naturally 

 immune fowl, especially into those in which previously retrogression of such 

 a tumor had taken place, the successful inoculation with a second tumor may 

 be prevented either through lack of a stroma reaction or through the subse- 

 quent accumulation of lymphocytes. However, later investigations did 

 not confirm the theory of a lack of a stroma reaction as the mechanism under- 

 lying the destruction of the grafts in immunized mice (Mottram and Russ, 

 Murphy, Tyzzer and Levin). We and our associates likewise have failed to 

 observe a phenomenon corresponding to it in the case of normal tissues, al- 

 though Cora Hesselberg and the writer noticed a diminished vascularization 

 of homoiogenous as compared with autogenous grafts. 



Russell and Bashford, believing that active immunity depends upon a lack 

 of stroma reaction, assumed that this immunity can manifest itself directly 

 after transplantation only, before the tumor has been incorporated in the host 

 tissue and has begun to grow, However, there is every reason for believing 

 that a retrogression of homoiogenous tumors may be caused by an active immu- 

 nity which develops in the host during the period of growth of the transplant. 

 In this case there is then an active immunity which does not depend upon a 

 lack of stroma reaction. Moreover, Russell himself noted that in actively 

 immunized animals a small tumor nodule may occasionally grow for some time, 

 but subsequently retrogress. Here, too, the active immunity causing the retro- 

 gression does not depend upon the stroma reaction for its manifestation. It is 

 known that under certain conditions homoiogenous and even heterogenous 

 tumors are able to remain alive and even to grow for some time without 

 possessing a stroma. We may then conclude that the lack of a stroma reaction 

 does not play a significant role in the active immunity against homoiogenous 

 tumors. 



In a somewhat different way, also, Greene attributes to the stroma a promi- 



