FERTILISATION 197 



trend of physiological research in recent years has been to show 

 that the correlation that exists even between remote parts of 

 the body is often extraordinarily close, and that in all proba- 

 bility there is not an organ or structure that is not dependent 

 in its growth and activity upon chemical substances, elaborated 

 by other and sometimes distant parts of the body, and carried 

 thence in the circulating blood. Thus a change in the whole 

 metabolism, producing palpable modification in whole groups 

 of characters, may be induced experimentally in the individual, 

 by interfering with or removing one particular organ. This is 

 well shown in the various kinds of correlation existing between 

 the organs of internal secretion. Again, a change in the 

 environment may directly affect the metabolism, and so influence 

 all the characters of the body. To the physiologist, therefore, 

 a so-called unit character cannot readily be regarded as some- 

 thing represented by a substance located originally in a chromo- 

 some or chromomere. Such a view, as Verworn l remarks, is 

 " too morphologically conceived." It is more in keeping with 

 the physiological view of life to regard the characters of the 

 individual as manifestations of a particular kind of metabolism, 

 which is itself partly the outcome of environmental influences, 

 and partly the developmental result of the sort of metabolism 

 that existed in the germ cells from which the organism was 

 derived. According to this view, it is clear that the presence of 

 any one characteristic may exert an influence upon many, if not 

 upon all, the other characteristics, and that, even in heredity, 

 one canrfot hope to alter any single organ or structure without 

 affecting, in some slight degree at any rate, all, or nearly all, 

 the other parts of the body. It may be argued, therefore, in 

 criticism of the Mendelian conception of unit characters, that it 

 takes little or no account of the metabolism of the organism as a 

 whole. Thus it has been shown that in the case of presence or 

 absence of hair pigment (which has been regarded as a simple 

 example of alternate characters, such as can be superimposed 

 experimentally upon other characters in the course of two 

 generations), there is a pronounced correlation between albinism 

 and other characteristics of the body, these characteristics 

 dep'ending for their existence upon a common metabolism. 

 1 Verworn, loc. cit. 



