72 RALPH S. LILLIE. 



The universal presence of proteases in cells seems to be the ex- 

 pression of this necessary condition, since in all cells the struc- 

 tural proteins are capable (under certain conditions) of regression 

 and translocation, i. e., of being utilized as food-material else- 

 wherethe proteins of one region of the cell or organism acting 

 as reserve, so to speak, for construction at other regions. Such 

 a condition is apparently necessary for the normal regulation 

 of cell-structure and activities. For the continuance of normal 

 cell-activity a proper ratio between structural and metabolizing 

 substance must be preserved; 1 hence in every cell the conditions 

 must be present for reducing proteins and other materials to a 

 non-specific and diffusible form, in addition to the conditions for 

 specific synthesis. 



By the synthetic activity of the protoplasm these relatively 

 simple substances are united and chemically remodeled so as to 

 form a variety of more complex compounds of which the most 

 individualized and specific are the proteins. The term specific 

 is here used as meaning peculiar to the particular organism or 

 cell under consideration, and not occurring elsewhere. It is not 

 a coincidence that living organisms, the most complex systems, 

 in the structural sense, occurring in nature, are also the most 

 complex in the purely chemical sense; and all of the evidence 

 indicates that the structural complexity is the expression or 

 consequence of the chemical complexity. 2 The essential reason 

 for this appears to be that a high degree of chemical specificity 

 or individualization is the necessary prerequisite for structural 

 complexity, and that chemical specificity depends largely upon 

 peculiarities of stereochemical configuration. The number of 

 individualized isomers in the case of any organic compound 

 increases rapidly with increase in the number of asymmetric 

 carbon atoms in the molecule. Hence the proteins, formed of 

 linked amino-acids, most of which are asymmetric compounds, 

 exhibit the possibilities of chemical individualization to a greater 

 degree than any other known class of compounds. It is further 

 significant that proteins which are specifically distinct chemi- 



1 E. g., in a starving protozoon or planarian the normal structure and propor- 

 tions are preserved, in spite of the decrease in size. 



2 Similarly with structural diversity, whether in the same organism or in dif- 

 ferent organisms. A corresponding chemical diversity is implied. 



