I7O LEO LOEB. 



rence and it can be considered as an intracellular transplantation. 

 Homoiotransplantation succeeds in this case as well as autoreac- 

 tion. Indeed it is a transplantation which usually occurs under 

 homoio conditions. Furthermore, just as in the case of the more 

 primitive tissues a reaction of incompatibility occurs after hetero- 

 transplantation, in a corresponding way a reaction of incompati- 

 bility occurs, when chromosomes of germ cells with different 

 species differentials meet, as the experiments of Baltzer, Tennent, 

 Moenkhaus, Guyer, Newman and others have shown. With this 

 conclusion is even in agreement the cross-fertilization between 

 widely different classes which have been made possible through 

 the discovery by Jacques Loeb of a method permitting such 

 hybridizations. In this case the incompatible chromosomes are 

 eliminated. 



There is an additional similarity between heterotransplantation 

 and heterofertilization. While in both cases the incompatibility 

 increases on the whole in correspondence with the distance of the 

 species, there is no absolute agreement between the effect of 

 heterofertilization and heterotransplantation on the one hand and 

 the relationship of the species on the other hand and in both cases 

 reciprocal relations may lead to very divergent results. 



There exists on the other hand, as far as we can judge from a 

 study of recorded hybridizations, one noticeable difference be- 

 tween the reactions of chromosomes and tissues. In the latter 

 there is an indication that the incompatibility between species dif- 

 ferentials increases in the course of ontogenetic and phylogenetic 

 development. A study of hybridization on the other hand does 

 not suggest a greater mutual tolerance of chromosomes of dif- 

 ferent species in invertebrates as compared to those of verte- 

 brates. 



LACK OF THE HOMOIO SENSITIVENESS IN CERTAIN MAMMALIAN 



TUMORS. 



We have so far assumed that all mammalian tissues possess 

 the individuality differential and call forth reactions against the 

 homoiodifferentials. In general this statement is correct. There 

 exists, however, at least one notable exception to this rule. 

 There are certain tumors which are able to grow with the same 



