PRESIDENTIAL ADDRESS. 27 



It will be readily seen that this theory adapts itself to the 

 broadest conception of heredity and, if true, accounts for the 

 transmission of functionally produced modifications as well as 

 the selection of such accidental ones as prove advantageous. 

 But to the ordinary mind this strictly materialistic explanation 

 of heredity seems crude and is to a large extent unintelligible, 

 and the doctrine of pangenesis has gained few adherents 

 among scientific men. They fail as a rule to comprehend 

 Mr. Darwin's gemmules and to understand how they should 

 behave in the manner required by the theory. 



Very much of this difficulty, however, is cleared away by 

 the admirable exposition of Mr. Herbert Spencer of the na 

 ture of what he calls physiological units. To the biologist the 

 organic unit is the cell and when he has explained the nature 

 and action of cells he thinks he has gone far enough. But the 

 facts of heredity cannot be explained by any phenomena man 

 ifested by cells. Between the cell or morphological unit in 

 biology and the molecule of a highly complex organic com 

 pound, such as albumen, the highest class of chemical units 

 no intermediate element had hitherto been recognized. Mr. 

 Darwin's gemmule is clearly such an intermediate element, 

 and the question at once arose, is there any such ? Mr. Spen 

 cer has, I think, shown beyond the possibility of doubt that 

 there is and must necessarily be such an element a unit which 

 is not chemical, since it possesses life, and which is not the 

 morphological unit or cell, but is that of which the active part 

 of every cell consists, and is appropriately termed the physio 

 logical unit. I have elsewhere* undertaken to show that life 

 may have resulted from a process of chemical recompounding, 



* American Naturalist, Vol. XVI, December, 1882, p. 976. Dynamic 

 Sociology, New York, 1883, Vol. I, p. 311. 



