278 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



all the physicochemical laws of action and reaction which have been 

 observed to occur within living things. In all physicochemical 

 processes within and without the organism by which energy is cap- 

 tured, stored, transformed, or released the actions and reactions are 

 equal, as expressed in Newton's third law. 



Actions and reactions refer chiefly to what is going on between 

 the parts of the organism in chemical or physical contact, and are 

 subject to the two dynamical principles referred to above. Inter- 

 actions, on the other hand, refer to what is going on between material 

 parts which are connected with each other by other parts, and cannot 

 be analyzed at all by the two great dynamical principles alone without 

 a knowledge of the structure which connects the interacting parts. 

 For example, in interaction between distant bodies the cause may be 

 very feeble, yet the potential or stored energy which may be liberated 

 at a distant point may be tremendous. Action and reaction are 

 chiefly simultaneous, whereas interaction connects actions and reac- 

 tions which are not simultaneous; to use a simple illustration: when 

 one pulls at the reins the horse feels it a little later than the moment 

 at which the reins are pulled — there is interaction between the hand 

 and the horse's mouth, the reins being the interacting part. An 

 interacting nerve-impulse starting from a microscopic cell in the brain 

 may give rise to a powerful muscular action and reaction at some 

 distant point. An interacting enzyme, hormone, or other chemical 

 messenger circulating in the blood may profoundly modify the growth 

 of a great organism.. 



Out of these physicochemical principles has arisen the conception 

 of a living organism as composed of an incessant series of actions and 

 reactions operating under the dynamical laws which govern the 

 transfer and transformation of energy. 



The central theory which is developed in our speculation on the 

 Origin of Life is that every physicochemical action and reaction 

 concerned in the transformation, conservation, and dissipation of 

 energy, produces also, either as a direct result or as a by-product a 

 physicochemical agent of interaction which permeates and affects the 

 organism as a whole or affects only some special part. Through such 

 interaction the organism is made a unit and acts as one, because the 

 activities of all its parts are correlated. This idea may be expressed 

 in the following simplified scheme of the functions or physiology of the 

 organism : 



