22 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



vidual, species, and so on, these depend in all probability on the structure of 

 the egg and on organ- forming substances which are distributed in a definite 

 and characteristic manner in the egg of each species, and on the interaction 

 of the organ- forming substance with the nuclear genes, in accordance with 

 the fact that genes have a specific relation to organ peculiarities of individuals 

 or species. 



There exist, then, in the fertilized egg not only the precursors of the organis- 

 mal differentials but also those of the various organ and tissue differentials, 

 which latter, singly or in their totality, likewise characterize an individual or 

 species and which constitute the mosaic parts which have served in the study 

 of Mendetlian heredity. 



Comparative anatomy, embryology, genetics and biochemistry have thus 

 contributed to the analysis of what may now be designated as organismal and, 

 in particular, as individuality differentials on the one hand, and organ and 

 tissue differentials on the other hand. Furthermore, at about the time when 

 biochemists, anatomists and embryologists began to discuss the problem of the 

 chemical and structural basis of species differences, an important additional 

 stimulus to the analysis of this problem was given and new viewpoints were 

 revealed by the development of immunology. Following the discoveries of 

 Pasteur, Behring, Roux, Buchner, Ehrlich, Metchnikoff, Gruber, Kraus and 

 others concerning the production of an active and passive immunity against 

 microorganisms and their toxins, and the mechanisms underlying this im- 

 munity, it was found by Bordet, Tschistowitch and other investigators, that 

 similar immune reactions can be called forth against bodyfluids and cells of 

 organisms belonging to different species. As a result of this immunization 

 various kinds of antibodies, such as precipitins, agglutinins, hemolysins and 

 complement fixing substances are produced, corresponding to the antibacterial 

 and antitoxic substances which had previously been discovered. These find- 

 ings suggested the possibility of differentiating different species by means of 

 such antibodies. If blood sera or other substances of a protein nature from 

 various species were injected repeatedly into rabbits or other animals, immune 

 sera were obtained against the antigens used. The interactions of these immune 

 sera with the antigen and with other analogous substances obtained from 

 nearly related or more distant species were then compared and the results of 

 these tests served as indicators of the relationship between the various species 

 (Grunbaum, Nuttall). 



In a similar way the interaction of performed bodyfluids and cells derived 

 from different species was tested directly (Friedenthal). Landsteiner (1901) 

 studied the interaction of individual human sera and erythrocytes in order to 

 find differences between different individuals; instead, he discovered the ex- 

 istence of four different blood, groups into which human beings can be ar- 

 ranged. Hamburger (1901), and later, Abderhalden, pointed out that proteins 

 derived from a foreign species are toxic if introduced parenterally and that it 

 is the function of the gastrointestinal organs to split these proteins into simpler 

 constituents, which are no longer characteristic of the species from which they 

 were derived and which at the same time have lost much of their toxic char- 



