Preface 



The study of individuality began when human beings observed others, 

 noted their structure and functions, their attitudes and actions. At a 

 later stage the physiologist and psychologist recognized that in the 

 individualities separate constituents can be distinguished and they extended 

 the concept of individuality to other organisms than man. In this book the 

 attempt has been made to distinguish between two types of individuality: 



The first one is the mosaic type which represents the sum of the par- 

 ticular organ and tissue characteristics (organ and tissue differentials) 

 which determine structure, metabolism, motor and psychical activities and 

 the component parts of which differ in different individuals. These multiple 

 characteristics are combined into a composite or mosaic which is peculiar to 

 each individual. 



The second type of individuality which may be designated as the essential 

 individuality is characterized by the presence of a chemical factor — the 

 individuality differential — which is common to the different organs and 

 tissues of each individual and which differs from the corresponding chemi- 

 cal characteristics of the organs and tissues of every other individual. This 

 concept emphasizes the oneness of the individual which depends upon the 

 presence of a common and unique factor in all of his essential parts. 



In the same sense in which individuality differentials characterize individ- 

 uals, there are species, order and class differentials each possessing a specific 

 chemical constitution which characterizes the larger groups of organisms. All 

 these various differentials may be grouped together as organismal differentials 

 in contrast to the organ and tissue differentials which, as mentioned, constitute 

 the mosaic individuality. While it is thus possible to distinguish sharply be- 

 tween these two types of differentials and between the corresponding defini- 

 tions of individuality, various kinds of interactions take place between the 

 organismal and organ differentials and these interactions are required to make 

 of the individual an integrated whole. 



In the following chapters these various aspects of individuality, including 

 the psychical, are analyzed, but only as far as the principles underlying these 

 phenomena are concerned and no attempt has been made to present a detailed 

 or complete account of all the data which may have a bearing on the problems 

 involved. 



The starting point of this analysis was a series of investigations on the 

 transplantation of normal and of tumor tissues which the author and his col- 

 laborators have carried out in the course of about forty-eight years, some of 

 which, especially those dealing with inbred strains of mice, have not yet been 

 published. To make possible a unified account and interpretation of the various 

 aspects of individuality, it was necessary for one person to undertake this 

 work, rather than to edit a collective book written by specialists in the different 



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