86 THE BEGINNINGS OF LIFE. 



dissimilar does not readily segregate them, but that it 

 readily segregates them if they are widely dissimilar. 

 Thus, these two extreme contrasts, the one between 

 physical mobilities, and the other between chemical 

 activities, fulfil in the highest degree a certain further 

 condition to facility of differentiation and integra- 

 tion.' 



Thus, then, the very fact that organizable matter is, 

 in the main, compounded of elements with such dis- 

 similar properties, affords a strong a priori presumption 

 that such organizable matter would be most unstable, 

 and most prone to undergo metamorphic changes under 

 the influence of even slight changes of condition such 

 as might operate without appreciable result upon the 

 majority of inorganic substances. The properties of 

 the various protein substances which form the all- 

 essential constituents of living tissues, are found to 

 correspond entirely with these a priori requirements. 

 This can scarcely be better shown than it has been 

 by Mr. Spencer when he wrote 1 : c It is, however, the 

 nitrogenous constituents of living tissues that dis- 

 play most markedly those characteristics of which 

 we have been tracing the growth. Albumen, fibrin, 

 casein, and their allies are bodies in which that 

 molecular mobility exhibited by three of their com- 

 ponents in so high a degree is reduced to a mini- 

 mum. These substances are known only in the solid 

 state : that is to say, when deprived of the water 



1 Loc. cit. p. 12. 



