176 LEO LOEB. 



The latter, however, differ from the former in their sensitiveness 

 to strain differences within the same species. In addition there 

 may furthermore perhaps be found some differences in the be- 

 havior towards heterotoxins of invertebrate and embryonic tissues 

 on the one hand and of transplantable tumors on the other hand. 

 From these curves differs very markedly the curve of the adult 

 tissue of the higher vertebrates and similar to this is the curve of 

 the large majority of the tumors, namely of those which generally 

 are not transplantable, although in a limited number of individ- 

 uals of the same species they may perhaps grow (Curve III.). 

 The adult tissue of amphibia and fishes represents a transitional 

 condition between type I. or II. and III. 



CELLULAR AND PSYCHICAL DISCERNMENT OF INDIVIDUALITY. 



We have shown that the cells of our body are able to discern 

 in a quantitatively graded manner not only the difference between 

 their own kind, between the constituent parts of the same indi- 

 vidual on the one hand, and the cells of other individuals of the 

 same species, on the other hand, but that they are able even to 

 recognize in a graded manner degrees of relationship between 

 members of the same family. We found especially the lympho- 

 cytic reaction a quantitative indicator of this relationship. We 

 must therefore conclude that there are graded biochemical differ- 

 ences within the same family which these individual cells discern, 

 and to which they react. These reactions represent as far as we 

 are aware, the finest biochemical reaction known at the present 

 time and on the basis of these reactions we may in a tentative 

 manner postulate a graded system of contact substances which 

 regulate the interaction of various tissues. 



To return in conclusion to the starting point of our discussion, 

 namely, the usual meaning of individuality, we saw that in the 

 main, it designates a social-psychical way of reaction. We are 

 able to differentiate between individuals as a result of certain 

 functions of our central nervous system. If we now inquire 

 how far the development of this kind of individualization is par- 

 allel to the power of cells of higher vertebrates generally to dis- 

 cern individuality, we are handicapped by the lack of data as to 

 the power of animals to discern not merely members of a species, 



