HEREDITY AND TRANSPLANTATION OF TUMORS 381 



homoiogenous constituents of the antigens. Correspondingly, the immunity 

 which is found in animals in which a homoiogenous tumor has retrogressed is 

 directed only against the same or against related homoiogenous tumors. 



In accordance with the theory that the organismal differentials are pri- 

 marily responsible for the compatibility between tissues, we have assumed that 

 it is the genes, or rather their derivatives, in the tumors which are strange to 

 the host which call forth and determine the intensity of the reactions of the 

 host against the transplant ; and that the genes and their derivatives which are 

 identical in host and transplant do not enter into these reactions, or do so 

 only to a slight degree. We thus define in a more exact manner the cause of 

 the reactions between host and graft. According to the terms of Mendelian 

 heredity, the genes, which differ in host and transplant, are dominant over 

 the genes which are identical, the latter being recessive, although as we have 

 seen in our discussion of the transplantation of normal tissues, there is the 

 possibility that also the latter may exert a certain effect. 



In agreement with the interpretation given here are the results which Eisen 

 and Woglom obtained in immunizing rats against the growth of a trans- 

 planted mammary gland adenocarcinoma, which had developed in a rat be- 

 longing to the inbred August strain; this strain was the offspring of a cross 

 between two inbred strains (990 and 1561). The mammary gland tumor could 

 be transplanted successfully into 100% of the August strain rats and into 

 78% of the 990 strain rats. Previous inoculation of embryo skin derived 

 from August strain rats was not able to immunize August strain rats; nor 

 was it possible to immunize 990 rats against the growth of the adenocarcinoma 

 by means of strain 990 embryo skin ; but embryo skin of August strain rats 

 was very effective in immunizing animals belonging to strain 990. This is a 

 good illustration of the fact that it is the strange genes which make possible 

 the development of efficient antigens, and that it is the degree of strangeness 

 of the individuality differentials in host and transplant which determines 

 the degree of the antigenic effectiveness of the normal tissues or tumors. 



Another difference between normal tissues and tumors or tumor-like tissues 

 has been noted by Furth in his experiments concerning the transmission of 

 leukemia in mice. He observed that in certain inbred strains a large propor- 

 tion of the animals become affected by this disease. If leucocytes from a 

 leukemic mouse were injected into other normal mice of this inbred strain, 

 leukemia developed in all the animals, but leukemia could not be transferred 

 to another strain in which spontaneous leukemia did not occur or was rare ; it 

 developed in 100% of F x hybrids between these two strains which had been 

 inoculated with the leukemic cells. There was a decrease in transplantability 

 in the F 2 , and still more so in the F 3 generation. In backcrosses from hybrids 

 F 1 to the susceptible parents leukemia developed in 100%, while in the back- 

 crosses from F x hybrids to the non-susceptible parents it took in 50%. 

 Leukemia arising in a hybrid F 1 could be transferred to all mice belonging 

 to the susceptible parent strain ; this is contrary to what should be expected 

 according to the theory of the organismal differentials and to what is actually 

 found in normal tissues and in mouse carcinoma. On the other hand, leu- 



