548 GENERAL PHYSIOLOGY 



the endless chain of transformations of energy which characterise 

 the life not only of the plants but also of the animals. The role 

 of light is similar to that of the heat that is introduced ; heat is 

 indispensable to life in both the plant and the animal body, and 

 serves to increase the intramolecular vibrations of the atoms, so 

 that the latter become inclined to rearrangements. But it is always 

 chemical energy that effects these rearrangements. In other 

 words, in the plant chemical energy must be already present in 

 the chlorophyll-bodies, and onlj' by the introduction and trans- 

 formation of photic energy is this so increased that it can accom- 

 plish the first cleavage of the molecule of carbonic acid, which has 

 such very important consequences. Where living substance with 

 its chemical energy is not already present, the introduction of 

 light cannot produce life. Thus, the chemical energy intro- 

 duced into the organic world along with the first living sub- 

 stance in prehistoric times, even now continues to work in all 

 living organisms, without ever having undergone a break in con- 

 tinuity. Life cannot be transferred from one organism to another 

 without the transference of living substance containing chemical 

 energy. It is a tiny quantity of both substance and chemical 

 energy that is transferred in the microscopic egg-cell to the off- 

 spring, but it is sufficient to ensure the continuity of both. The 

 chemical energy thus transferred makes reproduction possible, 

 gives the impulse to the continual transformation of constantly 

 greater and greater quantities of energy, in a certain sense by 

 ferment-like action, and finally causes a powerful development of 

 force in the adult organism. It is the original capital with which 

 the developing organism begins its dealings, and without which 

 its existence would be impossible. In this sense it can be said : 

 that form of energy from whieh in the last instance all the work 

 of the organic world is derived is chemical energy. The light and 

 heat introduced act only by making chemical energy available. 



It is evident that this is equally true of animals and of plants. 

 Out of the original chemical energy available in the plant not 

 only is the manifold external work of the plant supplied, but a 

 considerable quantity is stored up in the form of chemical 

 energy in the organic compounds of the plant-body. These com- 

 plex organic compounds afford food for the herbivore, while the 

 flesh of the herbivore does the same for the carnivore. Thus, with 

 plant-food energy comes to animals in chemical form and affords 

 potentials for the performances of the animal body, which are 

 distinguished so characteristically from those of the plants by 

 their powerful extrinsic development of force. In fact, the chemical 

 energy introduced into the animal body with the food forms the 

 sole source of the energy of the animal body, with the exception of 

 the small quantity of heat that acts from the outside upon all 

 organisms. The j^roof of this fact has been afforded in the most 



