36 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



be graded and in which a variety of tissues can be chosen for grafting provide 

 the opportunity not only for the analysis of the organismal differentials of 

 host and transplant, but also for the study of the interaction of various types 

 of tissues and cells and of the factors which determine the tissue equilibria ; 

 they may therefore serve also as a method which may be of value in building 

 up a physiology of tissues, in contrast to the physiology of organs which has 

 been so extensively studied in the past. Accordingly, we shall emphasize this 

 aspect of our investigations in describing our results. 



