62 PROTOPLASMIC ACTION AND NERVOUS ACTION 



entiated" protoplasm is not homogeneous, and it is 

 necessary to reach a clear conception of the essential 

 nature of this structure in the most generalized forms 

 of living substance if we are to be in a position to under- 

 stand the fundamental conditions of physiological activity. 



That metabolism is controlled by structure is seen 

 in many well-known physiological facts already referred 

 to in part; e.g., the course of development, with the 

 associated constructive metabolism, may in many eggs 

 or embryos be profoundly modified by artificially 

 altering the structure of the system. Developmental 

 processes are frequently initiated by mechanical means; 

 cases of regeneration illustrate this, or cases where 

 injury of the egg-surface (pricking in the case of the 

 frog's egg,^ or any kind of cytolytic action in echinoderm 

 eggs)"^ initiates cleavage and development. Mechanical 

 treatment causes stimulation in innumerable instances; 

 in others it causes inhibition. In all of these cases the 

 energy for the developmental or other response comes 

 directly or indirectly from metabolic processes. This 

 sensitivity to the action of mechanical agents, which by 

 their impact, pressure, or other effects locally modify 

 cell structure, is perhaps the clearest proof of the intimate 

 relations existing between structure and function in 

 living protoplasm. 



In physical chemistry the importance of structural 

 conditions as modifying factors in chemical reactions is 

 illustrated in the so-called heterogeneous catalyses. 

 In these phenomena the acceleration of reaction is 



^ Guyer, Science, XXV (1907), 910; Bataillon, Arch. zool. exper. 

 et generate, XL VI (19 10), 103. 



^ Loeb, Artificial Parthenogenesis and Fertilization, University of 

 Chicago Press (1913). 



