INTRODUCTION 17 



reactions between the tissue constituents and the blood serum of the host and 

 the transplant. We may then conclude that each organ and tissue of individual 

 A has in common a chemical factor which differs from the corresponding 

 factor in individual B ; but in addition, certain organs and tissues may possess 

 accessory or secondary individuality differentials, which are peculiar to these 

 organs and tissues. 



The individuals among the higher organisms possess, then, two kinds of 

 adaptive mechanisms : the first one is that represented by the functioning and 

 interaction of tissues and organs within the individual, and the second is based 

 on the fact that the tissues and organs in the same organism possess the same 

 individuality and species differential, and that other individuals or species 

 carry different organismal differentials which are graded according to the 

 phylogenetic relationship. In consequence of this functional and structural 

 constitution, very specific relationships have developed within the individual 

 organism and between the various inidviduals within the same species, genus, 

 order and class. These intricate and complex specificities of both the mosaic 

 and essential type in their totality constitute the characteristic feature of the 

 individual. 



However, within the functioning organism, as well as in the relations be- 

 tween different individuals, the organ and tissue specificities are more obvious 

 than the individuality differentials, the effects of which are of a more subtle 

 nature. Also, in the sphere of social-psychical relations it is the function of 

 organs, above all, the nervous system and the endocrines, which appears as the 

 significant element. Yet, the individual organism is an integrated whole and 

 changes in one organ and tissue are followed as a rule by changes in other 

 organs and tissues. This applies also to those organ and tissue modifications 

 which occur during the process of ageing and disease, and also to interactions 

 between organs which concern primarily vegetative functions, as well as those 

 which control the psychical-social activities, and both of these two latter kinds 

 of processes are linked together. Ever} 7 change in a part of an individual affects 

 the individual as a whole, although different types of interferences may differ 

 in their effects on other parts of the organism and on the individual as a whole. 



Individuality, especially its social-psychical aspect, entered the experience 

 of man in very early periods of history; it helped to shape tradition and was 

 one of its important components, and as such it took part in orienting the rules 

 of conduct and of law. Gradually, under its influence, philosophical systems 

 and various metaphysical concepts arose. But it was only during the 19th. 

 century that the concept of individuality was fully dissociated from its prac- 

 tical social implications and that it began to be considered a biological problem; 

 from then on observations and experiments in various fields of biology have 

 contributed to its analysis and more definite problems concerning the in- 

 dividual and individuality were formulated. We shall here record a few of the 

 principal contributions concerning the biological aspect of individuality. 



The botanist, Naegeli, conceived of a substance peculiar to each individual 

 or species and he distinguished it from other less important constituents of 

 the living matter as the idioplasm. It served as the carrier of the characteristics 



