GENERAL FUNCTIONS OF MICROBES 3 



circulation between the two kingdoms? How does nature 

 succeed in producing substances which are combustible, 

 putrescible and capable of fermentation from combinations 

 which have none of these properties ? Here are impenetrable 

 mysteries. One may perceive, however, that since combustion 

 and putrefaction are the means which nature employs to return 

 to the mineral kingdom what has been drawn from it in the 

 building up of plants and animals, the latter process must be 

 the converse of the former." 



Green plants get their carbon from the carbonic acid of the 

 air. In virtue of their chlorophyll activity they build up this 

 carbon into starch, cellulose, sugars and fats. This 

 carbohydrate synthesis then represents the accumulation of 

 energy. A green plant kept in the dark burns up its 

 hydrocarbons, returning them to the atmosphere. A dead 

 plant returns its hydrocarbons after a series of decompositions, 

 in the form of carbonic acid and water. A plant which has 

 been eaten by an animal supplies the animal with glycogen and 

 fats which are consumed in the course of muscular work and 

 respiration. Dying animals like dead plants return their 

 hydrocarbons to nature. Plants without chlorophyll and all 

 animals spend and dissipate the energy accumulated by the 

 chlorophyllous plants, energy derived entirely from the rays 

 of the sun. 



Nitrogen exists in the atmosphere, from which it enters the soil. 

 It exists in the dejecta of living animals and in the bodies of 

 plants and animals rotting on the surface of the earth. It 

 accumulates there in the mould or humus : plants take up the 

 nitrogenous matter of the soil in the form of salts of ammonia 

 and nitrates, and build up from them the vegetable proteins. 

 Animals which eat plants produce from these the animal 

 proteins. Animals and plants in decomposition, and the 

 excretions of animals in general, return their nitrogen to 

 fertilize the soil. 



Animals are in a certain sense parasites of plants, since they 

 are unable to build up by themselves, starting from mineral 

 elements, their hydrocarbons and proteins. Even in plants 



B 2 



