256 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



addition to this general reaction against homoiogenous tissue, a specific im- 

 munity against the particular individuality differential, which was used as 

 antigen, may also have developed. 



Rous believes that this acquired immunity manifests itself in the lack of 

 a stroma reaction in the immunized mouse towards the transplant; an in- 

 growth of capillaries and connective tissue from the host into the transplant 

 does not take place and the transplant dies as a result of this deficiency in 

 blood supply. A lack of stroma reaction has also been observed by Rous 

 in natural immunity, if a single transplantation of embryonal tissues is 

 made into an unfavorable host. Rous does not mention the appearance of 

 lymphocytes around the transplants in the immune hosts. A similar immune 

 reaction has been described by Russell and Bashford in the case of grafted 

 pieces of tumors, a mode of reaction which we shall discuss in a subsequent 

 chapter. 



If we wish to draw definite conclusions concerning the relations which 

 exist between the state of the organismal differentials and the degree of 

 differentiation and fixity of organs and tissues in various types of organisms, 

 we again suffer from the difficulty that transplantations of embryonal ma- 

 terial were not usually undertaken with this problem in mind. However, if 

 allowance is made for a certain degree of inadequateness in the data, we 

 may conclude that the range of transplantability in general is wider in the 

 phylogenetically more primitive classes of animals, and that among the latter, 

 in particular, it is wider in the more primitive urodele than in the anuran 

 amphibia ; that within certain limits in the ontogenetically earlier stages there 

 is found both a lesser degree of organ and tissue differentiation and fixity 

 and a lesser differentiation of the organismal differentials, and lastly, that 

 the range of transplantability decreases with advancing embryonal develop- 

 ment and differentiation. Furthermore, regenerating tissues in adult urodele 

 amphibia have been shown to behave in certain respects like embryonal 

 tissues; and corresponding to the increasing degree of organ and tissue 

 differentiation, which is attained with advancing regeneration, transplantabil- 

 ity of regenerating tissues likewise decreases. The earlier, less differentiated 

 tissues are still more plastic and amenable to environmental factors, while 

 the father advanced stages in embryonal development are more fixed in their 

 organ and tissue differentials and thus have a greater tendency to develop by 

 way of self-differentiation. This latter conclusion applies also to the regenerat- 

 ing tissue in the adult urodele. We find again, therefore, a relation between 

 the differentiation and fixity of organ and tissue differentials on the one hand, 

 and organismal differentials on the other hand, and in certain respects also 

 a parallelism between the development of organ and tissue differentials and 

 organismal differentials in the phylogenetic and in the ontogenetic series; but 

 this parallelism exists only in a general way. As stated above, gradations in 

 refinement of differentiation with advancing phylogenetic and ontogenetic 

 development can be more clearly recognized in the case of organs and tissues 

 than in the case of the organismal differentials. 



