144 LEO LOEB. 



tion." Within the same species differences of groups and strains, 

 varieties may arise. 



Transplantation into a different species we call " heterotrans- 

 plantation." Here, nearly related species, which interbreed, 

 further distantly related species, which do not interbreed, species 

 which belong to different genera, families, classes can be distin- 

 guished. To this spectrum of relationships correspond?, with 

 certain limitations, a spectrum of interactions of tissues after 

 transplantation. 



We judge individuality in man primarily by characteristic 

 social-psychical reactions. It is, therefore, I presume, originally 

 a term connoting psychical attributes. Each individual is sup- 

 posed to form an indivisible whole. It is one organism separate 

 and distinct from all others. No two organisms can be identical. 

 This finds the sharpest expression- in the conception of a soul 

 which is supposed to be the real bearer of the individuality, which 

 is unlike any other soul and indivisible. 



To the psychical individuality corresponds individuality of the 

 body. The body also is supposed to represent one indivisible 

 whole, different from every other body ; in short one common 

 factor uniting all the parts, and distinguishing them from all the 

 parts of other individuals. 



This conception, however, does not quite harmonize with the 

 mosaic such as has been revealed by Mendelian analysis of in- 

 heritable characteristics of organisms. Mendelian analysis has 

 shown an organism to consist of a very great number of unit 

 factors, the various unit factors being approximately the same 

 in many organisms of the same species, and the individuals dif- 

 fering from each other in the mosaic of unit factors of which 

 each one is composed. A common factor or set of factors present 

 in all parts of the organism and truly representing its individ- 

 uality is not provided for in this scheme. 



INDIVIDUALITY DIFFERENTIAL. 



And yet, such a characteristic present in all parts does exist. 

 It is the same everywhere in the same organism and differs in 

 different organisms. We may call this characteristic individual- 

 ity differential as far as it distinguishes individuals, and species 



