HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 89 



culture-medium the structure of the germ, its chemical composi- 

 tion, and the chemical composition of the culture-medium, are 

 all equally essential factors in the resulting growth-process. The 

 main difference is that each living cell, as soon as formed, is 

 capable of acting as a similar center of transformation when 

 transferred to another culture-medium; i. e., all of the necessary 

 parts of the proliferating system are multiplied equally; and so 

 far we have been unable to produce any artificial systems having 

 such properties. If we were to succeed in doing so, it is probable 

 that such systems would exhibit a much closer resemblance to 

 living organisms than any of the inorganic models hitherto used 

 for comparisons of the above kind. 



Obviously these fundamental resemblances between the two 

 types of system under comparison do not preclude infinite dif- 

 ferences in the details of structure, chemical composition, and 

 activity; but I am at present insisting upon the resemblances 

 because of the desirability of determining the class to which the 

 organic formative processes belong. The characteristic plas- 

 ticity and responsiveness of living matter undoubtedly depend 

 upon the fundamental features of its physico-chemical constitu- 

 tion. Starting with living material of this peculiar type of self- 

 regulating structure and chemical composition, the develop- 

 mental process has in the course of time become so evolved and 

 perfected that it now builds up with unfailing regularity the most 

 complex of organisms from the food and other materials furnished 

 to the germ from the surroundings. But the possibility of this 

 development has depended upon certain general pecularities of 

 physico-chemical constitution present from the beginning in the 

 living formative substance itself; and my aim in the present and 

 preceding papers is to indicate what seem to me the most essen- 

 tial of these peculiarities. 



The case of higher organisms presents numerous problems of a 

 more special kind, and most investigators in the field of heredity 

 have given their chief attention to these problems. It seems 

 clear that in these organisms other and more special mechanisms 

 of hereditary coordination and control have been superposed 

 upon the elementary physico-chemical mechanism which con- 

 ditions the fundamental proliferative activity. The fact that in 



