ORGANS AND TISSUES AS CRITERIA 459 



differs in individuals belonging to different races. However, the relative 

 frequency of these patterns in different finger pairs is similar in all races. 

 The ramifications of the cutaneous nerves seem to determine the situation of 

 the cores of the patterns and the distribution of the nerves apparently deter- 

 mines also the number and frequency of ridges in a unit area. In addition, 

 the differences in the shape of embryonal fingers, and especially in their 

 surface radius, influence the character of the patterns. These determining 

 factors underlying the formation of the patterns, which are thus complex in 

 nature and, to some extent, separate and independent of one another, are 

 largely transmitted hereditarily from parents to offspring in the same way 

 as other characteristics constituting the bodily and psychical mosaic. 



Of special interest, therefore, is the study of the skin patterns in so-called 

 identical twins, and here it has been found that the number of ridges com- 

 posing a pattern are much more similar than in bi-oval twins. But even in 

 identical twins certain variations in the patterns develop. It is therefore 

 assumed that these variations are phenotypic in nature, that is, they are 

 partly determined by environmental factors which are different in each twin, 

 and these latter variations are superimposed upon the genetic factors, which 

 are identical in both. 



There exist, also, sex differences in the skin patterns, but these disappear 

 in old age with the cessation of sexual function; they may therefore be 

 considered as constituting secondary or tertiary sex characters. 



The correlation, noted by Poll in human beings, between skin patterns and 

 certain characteristics of parts of the nervous system, especially conditions 

 which lead to insanity, is of interest. This investigator finds that certain 

 patterns predominate more in normal, and other types in insane persons, but 

 only in the male. However, as in the case of race characteristics, we have 

 here also to deal merely with statistical differences, the frequency with which 

 certain characteristics of skin ridges occur differing in normal and in certain 

 insane persons. Poll holds that this correlation is due to the fact that both the 

 nervous system and the skin are of ectodermal origin, an interpretation not 

 borne out by the findings of Kretschmer, that correlations exist also between 

 the character of the structure of the osseous system and of the panniculus 

 adiposus on the one hand, and the tendency to the development of certain 

 temperaments and of certain types of insanity on the other hand. In a similar 

 way, Graves has observed a certain correlation between the shape of the 

 scapula in a man and his power of resistance to injurious conditions. It may 

 therefore be assumed that the total skin pattern, as well as its single features, 

 depends upon genetic factors in the same way as the structures and function 

 of other systems depend upon genetic factors, and there exist, probably, on 

 this basis correlations between various organ systems, irrespective of their 

 embryonal relationship. 



II. Scents as criteria of individuality. Distinctive scents emanating from 

 animal organisms originate in the metabolic changes in certain organs; they 

 may therefore be classed among organ characteristics of the kind with which 

 we have to deal in this chapter. 



