RECENT PHYSIOLOGICAL PROGRESS 45 



The simple chemical theories of the re 

 spiratory and other metabolic processes 

 occurring in the body have likewise dis 

 appeared. The work of Pfliiger, Rubner, and 

 others has proved that in the living body 

 all these processes are regulated with the 

 utmost nicety, and that the seat of the 

 regulation lies within the living cells of 

 the body. By what physical or chemical 

 process regulation is brought about we do 

 not know. We have not even discovered 

 the agents employed in the process, although, 

 as already pointed out, there is reason to 

 believe that, in many instances at least, these 

 agents are intra-cellular enzymes. 



It has become evident also, that no simple 

 physico-chemical theory of muscular or other 

 physiological movements will suffice. The 

 processes which determine visible movement, 

 or transmission of excitation in living cells, 

 are an integral part of the many-sided 

 activity of the living cell, so that the 

 elementary problems of physiology cannot 

 be solved piecemeal. A physico-chemical 

 explanation of muscular movement, or of 

 secretion, or cell-nutrition, or nervous excita- 



