TRANSPLANTATION AND INDIVIDUALITY. 1 71 



readiness in another individual of the same species as in the or- 

 ganism in which they originated. This applies by no means to all 

 tumors, on the contrary the large majority of tumors behave in 

 this respect about like ordinary normal tissues which succumb to 

 the homoioreaction, and are only able to grow in the individual 

 a part of which they formed originally. Why there is a relatively 

 limited number of tumors which behave differently, why they 

 are able to withstand the injurious influences of homoiotoxins 

 which destroy the large majority of tumors, we do not know defi- 

 nitely. It is, however, very probable that these tumors also pos- 

 sess the individuality differential, and that their ability to with- 

 stand the homoiotoxins is due to their diminished sensitiveness 

 combined with an increased growth energy. Very often the 

 " homoioreaction " which is ordinarily lacking in these tumors 

 can be called forth through previous immunization of the host. 



It is exactly such tumors which lack the individuality reaction 

 which have been used by Tyzzer, myself and Fleisher and again 

 by Tyzzer and Little in order to study the inheritance of tol- 

 erance for grafted tumors. Tyzzer crossed for this purpose 

 white and Japanese waltzing mice; Fleisher and myself used 

 diverse strains of white mice. The strain differential is further 

 distant in the spectrum of relationships than individuality differ- 

 ential ; and Tyzzer and Tyzzer and Little dealt even with some- 

 thing akin to species differentials. Tyzzer believed that such 

 investigations may throw light on the character and origin of 

 tumors. While this view is probably not tenable, these investiga- 

 tions throw some light on the hereditary transmission of strain 

 and species differentials. I found here again an intermediate 

 mode of inheritance, while Tyzzer and Tyzzer and Little found a 

 more complex mode of inheritance. Again I suggested in inter- 

 preting my own as well as Tyzzer's results the presence of mul- 

 tiple factors, an interpretation which was subsequently adopted 

 by Tyzzer and Little. 1 



1 In a paper which just appeared after completion of this manuscript (C. 

 C. Little, Journal of Experimental Zoology, 1920, XXXI., 307) Dr. Little 

 expresses the opinion that the intermediate type of heredity is not the typical 

 mode of inheritance of the individuality differential. I believe that the views 

 which Dr. Little expresses are based on a lack of distinction between species 

 or strain differential on the one hand and individuality differential on the 



