IMMUNITY IN TUMOR TRANSPLANTATION 421 



become active. E. Harde also observed that heterotransplantation of mouse 

 tumors succeeds better in the brain than in the subcutaneous tissue, but this 

 applies only if nearly related species are used as hosts ; transplantation of 

 human tumors into the brain of rodents did not succeed, nor did the trans- 

 plantation of mouse tumors into the brain of guinea pigs. It seems that in this 

 organ the organismal differentials are less well developed than in most other 

 parts of the body. In this respect the brain behaves somewhat like the testicle, 

 where, according to Gheorgiu, heterogenous tumors can also be transplanted 

 successfully, and even more readily than into the brain. A further favorable 

 site is the anterior chamber of the eye (Smirnova, Greene and Saxton, 

 Greene) ; however, as to the behavior of the lymphocytes under these condi- 

 tions, no observations have been recorded so far. 



The views of different investigators concerning the role which lymphocytes 

 play in the immunization against transplanted tumors are, to some extent, still 

 contradictory. However, from a review of the results obtained and from our 

 own experiments, we conclude that in the growth of tumors the lymphocytes 

 play a part similar to that which we ascribed to them in the case of grafts of 

 normal tissues. Under certain conditions they may serve as indicators of a dis- 

 cordance between the individuality differentials of host and transplant. If host 

 and transplant belong to different species, polymorphonuclear leucocytes ap- 

 pear around the tumor and invade it, in addition to or instead of the lympho- 

 cytes. But, while with normal tissues the accumulation of lymphocytes and 

 their invasive activity may in certain cases become so pronounced that it leads 

 to the destruction of a great part of the transplant, with tumors this effect 

 seems to be much less marked. According to Woglom, the retrogression of 

 tumors is not necessarily associated with an increased activity of the lymph 

 glands, and in our early work on the retrogression of tumors in homoiogenous 

 organisms, whose individuality differentials differed markedly from those of 

 the hosts, we found no reason to attribute the retrogression to the activity of 

 the lymphocytes ; furthermore, Ishii and the writer, in a study of tumors which 

 had been weakened by heat previous to transplantation and which subsequently 

 retrogressed, did not observe an accumulation of lymphocytes around or in the 

 transplant sufficient to account for the retrogression ; we did find, however, 

 the formation of a strong connective tissue capsule around such tumors, which 

 may very well have helped to produce an inhibiting effect on the weakened 

 tissue. As in transplanted normal tissue, so also in transplanted tumors the 

 bodyfluids of the host may, to a large extent, determine the fate of the graft, 

 and they may be the principal factor concerned in this effect in the case of 

 tumors. 



It is, then, essentially the discrepancy in the individuality differentials of 

 host and transplant which causes the accumulation of lymphocytes, and which 

 may also increase the activity of connective tissue around the transplant ; and 

 it is likewise on the basis of a discrepancy between the organismal differentials 

 that immunity develops, which then may perhaps intensify the lymphocytic 

 reaction. If this interpretation is correct, we should expect a distinct accumu- 

 lation of lymphocytes to be lacking around autotransplants of spontaneous 



