286 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



movements may set in. Hence inadequate mechanical factors may be the 

 primary link which leads to these reaction chains. 



The results of these various sets of experiments so far discussed harmonize 

 with each other and also with the conception of the role that autogenous 

 morphogenic contact substances play in determining the tissue equilibrium. 

 Again, in this instance the reactions which take place if incompatible organis- 

 mal differentials are joined together, are due not merely to mechanical factors, 

 although mechanical factors are involved too in the maintenance of the 

 autogenous tissue equilibrium, but to the interplay of chemical contact fac- 

 tors of a more specific character which reside in the tissues. The effect of 

 unsuitable contact substances may be transmitted to neighboring areas. 



The higher developed the organism, the finer and more differentiated are 

 the organismal differentials which keep the various parts of the body in 

 equilibrium; this applies to the relation between neighboring parts of the 

 same type of tissue, as well as to the relation between neighboring tissues 

 which differ in type. In the more primitive organisms the individuality or 

 species differentials do not yet possess the same fineness as in higher organ- 

 isms ; at least the more delicate reactions, which would allow their manifesta- 

 tion, are lacking. Correspondingly, in these organisms embryonal or regenera- 

 tive organ and tissue formation is still possible and here, too, organismal 

 transplantations can be made. 



We now have analyzed two sets of facts in connection with the develop- 

 ment of the more primitive into the higher organisms. In the first place we 

 have noted the importance of organizer actions, which are very potent in 

 early embryonal stages, and their replacement with advancing embryonal life 

 by very complex systems of contact substances, functioning between adjoin- 

 ing parts of tissues and organs. Involved in this process, also, is the action 

 of distance substances or hormones, and, moreover, a step-by-step diminution 

 in growth potentialities and growth momenta, as well as in tolerance to strange 

 organismal differentials, as tissues and organisms progress from primitive to 

 more differentiated types. 



Furthermore, through transplantation experiments we have arrived at the 

 recognition of the relatively rigid character of the adult higher organisms. 

 Reactions of growth and differentiation are here very much diminished, except 

 in cancer growth, where the growth momentum of tissues may be very great. 

 Not only are the reactions against strange organismal differentials very 

 strong, but there exist, besides, some reactions against strange tissue differen- 

 tials. While in the more primitive organisms the organismal differentials play 

 a relatively less significant role and the interactions of tissues and organs and 

 the transformations which they undergo are very prominent, in the higher 

 organisms, concurrently with the diminution in potentialities of growth and 

 differentiation, and in morphogenic effects in tissues and organs, the reactions 

 against organismal differentials become very pronounced. There are found 

 in the higher organisms a marked fixity and strict regulation of tissues and 

 organs, which latter is maintained by the interaction of contact substances. 

 Thus an autogenous tissue equilibrium, which makes possible the existence 

 of integrated individuals, is established. 



