18 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



which were inheritable and transmitted from generation to generation. The 

 botanist, Strassburger, and the zoologist, O. Hertwig, localized this hereditary 

 substance in the nucleus. Subsequently, based on the work of Mendel and of 

 those who rediscovered and continued his investigations, the idioplasm became 

 more sharply defined and transformed into sets of discrete units, the genes, 

 which are contained in the female and the male germ cells, and especially in 

 the chromosomes of the cell nucleus. But in addition to these genes located in 

 the chromosomes, also constituents of the egg cytoplasm were considered as 

 determiners of the distinctive features of the organism, and some geneticists 

 (Correns, v. Wettstein and Kuhn) have assumed that genes, equivalant to 

 those situated in the chromosomes, may also exist in the cytoplasm of the egg. 



During the second half of the last century certain observations of surgeons, 

 who grafted tissues, pointed to a fargoing specificity and individualization in 

 the tissues comprising the higher organisms. The early experiments of the 

 French surgeon, Oilier, showed that only autotransplanted bone was able to 

 survive. Later experiments with skin and various other organs or tissues, such 

 as ovaries, and also with benign tumors, indicated that while homoiotrans- 

 plantation might perhaps succeed, autotransplantation was more favorable. 

 Yet, towards the end of the last century biologists found that the joining to- 

 gether of parts of embryos, as well as various kinds of homoiotransplantations 

 of invertebrate and lower vertebrate tissues, may give good results, and that 

 even heterotransplantations were successful under certain conditions. Not- 

 withstanding the experiences mentioned above, in the transplantation of 

 tissues in adult mammals no sharp distinction, as a rule, was made between 

 the results of auto- and homoiotransplantation. This was true even of the 

 work of Reverdin and Thiersch, who introduced skin-grafting into surgery 

 for therapeutic purposes. While, as stated, some of these observations sug- 

 gested that biochemical differences might exist between different individuals, 

 including those belonging to the same species, on the whole, the differences 

 between species were stressed rather than the differences between individuals, 

 and it was only within the last thirty-five or forty years that the distinctions 

 existing between the tissues of different individuals of the same species re- 

 ceived more attention. 



In the meantime, discoveries in biochemistry, comparative anatomy and 

 embryology had led to a further analysis of the specific structure of organisms. 

 The biochemist, Huppert, in 1895, in a lecture on the persistence of species 

 characters, referred also to the differences which, according to Rollett, existed 

 between the hemoglobins of different species as regards their elementary 

 composition, solubility and shape of crystals. He concluded that not only the 

 chemical constitution of various substances differs in different species, but 

 also that the metabolism of these substances is distinct and characteristic of 

 these species. Four years later Rabl, apparently under the influence of Hup- 

 pert's suggestions, discussed the differences in the microscopic structure of 

 homologous tissues in different species. While the histologic structure of the 

 liver could not be distinguished, it was discovered that the lens of the eye 

 differed in different species. This difference was maintained during the various 



