PREFACE xi 



We may safely assume that all qualitative phenomena, 

 including those of the living organism, are subject to 

 quantitative laws; but the determination of these laws, 

 while an essential object of scientific investigation, 

 cannot be regarded as its only object. The biologist is 

 primarily interested in the phenomena which are peculiar 

 to life and in the conditions under which these originate 

 and manifest themselves. As already indicated, growth, 

 development, and an integrative correlation of activities 

 are the chief distinguishing characters of organisms. 

 Underlying and determining these properties are the 

 fundamental or universal properties of protoplasm. 

 The essential problem in the physiology of growth (and 

 ultimately of development and heredity) is the problem 

 of the conditions of specific chemical synthesis in proto- 

 plasm. And the problem of integration resolves itself 

 largely into the problem of the conditions under which 

 protoplasmic processes, although spatially separated, 

 mutually influence one another; i.e., the problem of 

 transmission. For the solution of these problems we 

 require first of all a knowledge of the special conditions 

 under which the chemical reactions in protoplasm 

 proceed and influence one another. 



The general physical conditions under which chemical 

 reactions are initiated, accelerated or retarded, and 

 influence other reactions at a distance are undoubtedly 

 the same in living as in non-living matter; but the special 

 features of composition and arrangement in the proto- 

 plasmic system often render detafled analysis difi&cult. 

 Under these circumstances the study of "models" — 

 simple artificial systems in which the action of single 

 factors may be isolated and observed — may be of great 



