IMMUNITY IN TUMOR TRANSPLANTATION 413 



cellular substances, and we have every reason to believe that it is the 

 cytoplasmic elements which produce most actively the individuality differ- 

 entials rather than the paraplastic parts, although there is some evidence 

 that also the latter are not devoid of individuality differentials. Correspond- 

 ingly, we have found that normal cartilage elicits a weaker antagonistic 

 reaction of the host than does thyroid, which is rich in cells. As to the 

 inefficiency of lens and brain, this might be expected, because they do not 

 furnish very effective homoiogenous antigens in immunization experiments, 

 although as we have seen in an earlier chapter, they do contain homoio- 

 differentials. (d) There is, then, ample reason for the conclusion that it is 

 the organismal differentials, and in particular, the individuality differentials, 

 of the normal tissues acting as antigens, which call forth immunity against 

 the organismal differentials of the tumor. 



However, it is not necessarily the specific individuality differential of a 

 certain individual which serves as antigen against the identical individuality 

 differential in the tumor; but any individuality differential of the normal 

 tissue, which differs from the differential of the host animal and is therefore 

 strange to the latter, may function as antigen for the tumor. It may then 

 be assumed that any strange individuality differential activates, in the host, 

 reactions which are directed against all other strange individuality differen- 

 tials, provided both host and donor belong to the same species. 



We have seen that autogenous tissues cannot serve as antigens against a 

 subsequently transplanted homoiogenous tumor; likewise, it may be safely 

 assumed that tissues fom an animal belonging to a closely inbred strain cannot 

 function as an effective antigen in another animal of the same inbred strain. 

 The experiments of Eisen and Woglom on transplantation of a mammary 

 gland carcinoma in inbred strains of rats, to which we have already referred 

 in a preceding chapter, as well as certain experiments in which the production 

 of immunity was attempted against transplanted leukemic cells, are in agree- 

 ment with this conclusion. Rhoads and Miller observed that implantation of 

 normal mouse tissues may immunize mice against inoculation of mouse 

 leukemia; but while, according to MacDowell, embryo-skin of the inbred 

 strain Sto Li can produce resistance in strain C58 to leukemic cells of line I, 

 embryo-skin of strain C58 is not able to serve as an efficient antigen. However, 

 embryo-skin from hybrid (C58 x Sto Li)F x may call forth immunity in 

 strain C58. Evidently a single gene set of Sto Li present in the hybrid enables 

 the tissue of the latter to function as antigen and the presence of the gene 

 set of C58 in the hybrid does not interfere with the antigenic action of the 

 strange Sto Li gene set. In a similar manner, it seems that the agglutinogens 

 of the F 1 hybrid between two closely inbred strains, which has inherited a 

 gene set from each of the parents, possess the ability to produce antibodies 

 (agglutinins) in certain hosts and to absorb these agglutinins; in this case, 

 also, one strange gene set is sufficient for this purpose and the double gene 

 set is not required, (e) While a strange individuality differential of normal 

 tissue may call forth immunity against a transplanted tumor, the immunity 

 thus produced is not so strong as that following retrogression of a tumor. It 



