THE ACTIVITIES OF THE ORGANISM 87 



But the slightest impulse, an electric spark requiring 

 an almost infinitesimally small quantity of energy, 

 starts the combination of the gases, and this continues 

 until all is changed into water vapour. In this reaction 

 a large quantity of energy is liberated in the form of 

 heat. This heat becomes transformed into the kinetic 

 energy of the water particles which condense from the 

 steam formed in the explosion, and these particles 

 assume the temperature of their surroundings. The 

 energy which was potential in the explosive mixture, 

 and which was capable of doing work, still exists as 

 the kinetic energy of the water formed, but it has 

 become unavailable for any natural process of work. 



We have seen what is the general character of the 

 reaction series in the course of which carbon dioxide 

 and water become starch ; and then this, becoming 

 first soluble, and becoming associated with the ammonia 

 or nitrate taken into the plant, becomes protoplasm. 

 It is a reaction which differs from that just described, 

 in that available energy becomes absorbed and 

 accumulated, and retains the power of doing work. 

 It is not a reaction which can be initiated by an in- 

 finitesimal stimulus, but one in which just as much 

 energy is required in order that it may happen as is 

 represented in the energy which becomes potential in 

 the living substance generated. The first reaction 

 is one which may take place by itself ; 1 the other is 

 one which requires a compensatory energy-transform- 

 ation in order that it may happen. In the first 

 reaction energy is dissipated ; in the second one it 

 is accumulated. 



1 It is no use saying that apart from the electric spark the combination 

 would not take place, for we do not know that the and H of the mixture 

 do not combine very slowly, molecule by molecule, so to speak. At all events 

 there is no functionality between the infinitesimal quantity of energy supplied 

 by the spark, and the energy which becomes kinetic in the explosion. 



