544 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



Similar are the conditions in fishes, as Kodama has shown. Immune sera 

 against fish spermatozoa are organ-specific ; they react with spermatozoa of 

 their own as well as of related species, but not with the extract of fish muscle. 

 However, they are directed also against organismal differentials or their 

 precursors, as is shown by the fact that they may respond in a quantitatively 

 graded manner to the spermatozoa of different species of fishes, in accordance 

 with the phylogenetic relationship of the latter. 



The investigations on antisperm immune sera present an interesting prob- 

 lem, inasmuch as in this case we may have to deal with antigens which are 

 constituents not of somatic cells and tissues, but of germ cells from which 

 the somatic tissues develop, after sperm and egg have united during the 

 process of fertilization. These germ cells must, then, possess substances, 

 which behave like species differentials, as well as the precursors of substances, 

 which distinguish different individuals. They must, in addition, contain 

 substances which are specific for this type of cells and which correspond 

 therefore to organ differentials. But these differentials would not be identical 

 with the fully developed substances present in the adult somatic tissues; in 

 general, the specific substances present in the germ cells would represent, 

 rather, the precursor differentials, from which the substances in the adult 

 organism develop. This follows from what is known of the mechanism of 

 embryonal development and from investigations on the lens of the eye and 

 the brain, which indicate that also the antigenic function of the organ 

 differentials arises only in the course of embryonal life. However, the 

 possibility exists that, after all, the immune sera against spermatozoa do not 

 develop in response to antigens contained in the spermatozoa proper, but to 

 a constituent of the spermatic fluid ; still even then these antigenic constituents 

 would presumably not be derived entirely from ordinary somatic tissues, but 

 also from constituent parts of the spermatozoa or of the cells from which 

 the latter develop. This is suggested by the fact that also autogenous sub- 

 stances may in this instance have antigenic power. 



10. It is possible to immunize rabbits against the yolk of the chicken egg. 

 The antiserum thus produced forms specific precipitates with the egg yolk 

 of fowl, but not with their blood serum or with chicken embryo extract. We 

 have to deal, here, with organ-specific substances. The reaction is strongest 

 with the egg yolk from fowl, while a weaker reaction takes place with the 

 yolk from other birds, but not with the yolk of fish or reptile eggs (Seng). 

 There exists in^ this case, therefore, a certain quantitative gradation which 

 corresponds to the systematic relationship of the organisms involved; but this 

 correspondence is not complete, inasmuch as the intensity of the reactions 

 among different species of birds does not seem parallel to their relationship; 

 and, furthermore, the reactions do not agree with the serum precipitin 

 reactions. There is, then, present in the yolks of eggs a system of substances 

 which differ among themselves in their structure in a manner which cor- 

 responds, to some extent, to the differences in systematic relationship ; yet 

 these relationship differentials in the egg yolk appear to be independent of 

 the organismal differentials of the serum proteins. This is perhaps due to 



