546 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



organismal differentials can give rise to distinct antibodies, which may be 

 separated by means of specific absorption. This relationship between organ 

 and organismal differentials is further confirmed by a study of the origin 

 of the organ differentials during embryonal development. Von Szily has 

 shown that human fetal lens does not yet possess the marked organ-specificity 

 which is displayed by the adult lens, and that, correspondingly, the anti- 

 human fetal lens serum reacts also with human serum-albumin. Hektoen 

 and Schulhof confirmed this finding, although they did not observe it as 

 regularly as von Szily. In addition, the immune serum against fetal lens 

 shows a greater affinity for lens material from the same species than for that 

 from a more distant species; both of these reactions, indicating the presence 

 of organismal differentials in the fetal lens, may be lost in the course of 

 further differentiation of the lens tissue. We may then conclude that in the 

 fetal lens, which differs also structurally from the adult lens, organismal 

 differentials are more and organ differentials less pronounced than in the 

 case of the adult lens, and that as the result of complete structural differentia- 

 tion the significance of the organismal differentials diminishes, while that of 

 the organ differentials increases. Similarly, Witebsky finds that the organ- 

 specific lipid constituent of the brain appears only when a certain stage of 

 embryonal development has been reached, and that it is not yet present in 

 the brain of very young embroys. 



During embryonal development, it may be assumed, we have at first to 

 deal with substances in which the organismal differentials are prominent, 

 but in the course of further embryonal development changes tending toward 

 greater differentiation of the parenchyma and toward the formation of 

 paraplastic substances take place, which are specific for a particular organ, 

 and concomitantly with the increase in organ specificity the organismal 

 specificity decreases or may be lost almost entirely, at least as far as serological 

 tests indicate. The substances endowed with a marked organ specificity are 

 formed therefore from substances which possess a greater organismal 

 specificity. With the increasing complexity of an organism, not only the 

 organismal differentials become more refined — as is indicated by the trans- 

 plantation method — but also the organ specificity becomes more pronounced. 

 An analogous process takes place continuously in certain tissues during adult 

 life. Certain cells in which the organismal differentials are in all probability 

 as yet preponderating, become transformed into material in which these 

 differentials decrease in importance or are lost altogether, and in which 

 correspondingly the organ differentials begin to predominate. Such a process 

 seems to occur during the transformation of epidermal cells into keratin, 

 and presumably also during other tissue differentiations, and this change in 

 the differentials is apparently a characteristic feature of tissue differentiation 

 in general. 



Organ differentials occur then, ordinarily, in combination with organismal 

 differentials. In order to immunize against an organ differential of a non- 

 protein nature it is usually necessary to employ protein substances which 

 possess different species differentials and which act as carriers for the organ 



