14 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



However, a disequilibrated condition may occasionally be observed even 

 after allotransplantation, for instance, if pigmented skin is transplanted into 

 a defect in white skin of the same guinea pig. Notwithstanding the identity of 

 the individuality differential in this case, the transplanted pigmented epidermis 

 begins to infiltrate the neighboring white epidermis for a considerable time, 

 but ultimately a new tissue equilibrium is established and then the autogenous 

 tissues live harmoniously side by side. The pigmented epithelium is the more 

 active, vigorous tissue, and stimulated by the processes connected with and 

 following transplantation it asserts its superiority over the white epithelium 

 until this stimulation has died out ; yet neither connective tissue nor lympho- 

 cytes of the host are unduly activated under these conditions, because host and 

 graft possess the same individuality differential. 



There exists, then, a mutual adaptation to one another of tissues bearing the 

 same organismal differential, and there exists, also, a mutual adaptation be- 

 tween the blood plasma and the various tissues belonging to the same in- 

 dividual. It is these harmonious interactions which make the unity of the 

 organism possible and which are perhaps the most characteristic feature of 

 the living organism as an individual. But not only are the substances charac- 

 teristic of each individual different from those characteristic of any other 

 individual and in this sense specific; there is, besides, a second type of speci- 

 ficity, which may be designated as specific adaptation. By specific adaptation 

 we mean that it is the individuality, species, order or class differentials, in 

 general the organismal differentials, attached to the various tissues or to sub- 

 stances derived from these tissues, which determine how suitable and effective 

 the interactions between the tissues and substances are in the performance of 

 certain functions. If the respective organismal differentials are the same in the 

 tissues or substances, the interaction is most perfect. This statement applies, 

 for instance, to the interaction between tissue extracts, blood plasma and 

 blood serum. The character of the organismal differentials attaching to these 

 various substances determines how effective the coagulating power of the 

 extract is, and how effective also the inhibiting action of the blood serum will 

 be. 



We may then distinguish tivo types of adaptation within the organism. The 

 first one is well recognized; it is represented by the normal interaction of 

 various organs and of parts of organs, and by the transmission of stimuli 

 through the nervous system, through hormones, and through certain other 

 mechanisms. This is the basis of what might be called the mosaic type of in- 

 dividuality. The second type is the adaptation which depends on the identity 

 of the individuality differentials of tissues. The integrity of the organ func- 

 tions is largely based on this identity of the organismal differentials. But in 

 addition a number of chemical interactions in the organism, of which only 

 one example has been mentioned, depend specifically on the character of the 

 organismal differentials which are carried by these substances. This is the 

 basis of what might be called the essential individuality, in contrast to the 

 mosaic type. 



Under some conditions normal tissues act as though they were abnormally 



