378 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



of the same kind of tumor, or of a tumor resembling the first one, as far as 

 the constitution of their organismal differentials is concerned. 



Gorer has observed that when a transplanted tumor has retrogressed, hemag- 

 glutinins appear in the blood of the host, which are directed against the 

 erythrocytes of the donor of the tumor. He could show that when certain 

 strains of mice and certain tumors were used, there were several kinds of 

 hemagglutinogens present in the red corpuscles of the donor of the tumor 

 which gave rise to the formation of hemagglutinins, and the number of these 

 agglutinogens seemed to be approximately the same as the number of "sus- 

 ceptibility factors" for the growth of the tumors, as determined by the propor- 

 tion of takes in the F 2 and backcross generations of hybrids between two 

 strains varying in their susceptibility to the tumor, in accordance with the 

 theory of Tyzzer and Little. He concludes, therefore, that it is the hemag- 

 glutinogens which represent the genetic factors needed for the growth of a 

 transplanted tumor. Lumsden also noted in rats, in which tumors had 

 retrogressed, the presence of hemagglutinins for the erythrocytes of the donor 

 of the tumor. As we shall see later, it is unlikely that the number of factors 

 needed for the growth of a transplanted tumor can be determined in a valid 

 manner by the method mentioned. However, it is probable that differences in 

 the constitution of the individuality or species differentials of cells and tissues 

 in different individuals or species extend also to the erythrocytes, and that 

 here they may be represented by agglutinogens, and that the constituents of 

 the individuality and species differentials in the tumor cells, which are strange 

 to the host, give rise to several kinds of immune substances, one of which 

 consists of hemagglutinins. As stated, we believe that it is the genes of the 

 tumor, which are not represented in the host, which are the precursors of 

 strange constituents of the individuality and species differentials in the tumor, 

 and which thus, indirectly acting through the organismal differentials, may 

 give origin to processes of immunity and thus help to determine the fate of 

 the transplanted tumor. 



As to the determination of the "susceptibility factors" necessary for the 

 growth of a tumor in a host by counting the number of takes in the F 2 hybrids 

 between a favorable and an unfavorable strain, this is in principle the method 

 which is used for establishing the number of multiple factors required for the 

 appearance of a character in an individual, in case the father and mother 

 strain differ in the number of the genes, needed for this purpose, which they 

 contribute to the fertilized egg. In regard to the number of "susceptibility fac- 

 tors" found by using this method of determination, this differs in each kind 

 of tumor; by making a sufficiently large number of assumptions as to the 

 number of factors directly concerned and by having recourse to modifying 

 factors, it will be possible, approximately, to fit all ratios found in the F 2 

 generation of hybrids into a certain formula; but it is difficult to see the 

 advantages gained by establishing such a formula applying only to one 

 particular tumor. However, the growth of a tumor depends not only upon 

 certain genes in the host,, but, as we have already indicated, various factors 

 of a primarily non-genetic nature help to determine the number of successful 



