96 ORGANIC FUNCTIONING 



the foodstuffs transforms directly into kinetic muscular energy. 

 But ultimately all the foodstuffs, except some small nitrogenous 

 residues, transform, by oxidation, into CO 2 and OH 2. In 

 inanimate and animate engines alike the input is food (fuel) and 

 oxygen, and the output is kinetic energy of movement, heat and 

 the waste substances. 



36^. The Role of Bacteria. It is only in exceptional 

 conditions that animal substances persist in nature (perhaps 

 petroleum has had animal origin). In general putrefactive 

 bacteria, with nitrifying species, reduce all proteins to CO 2, OH 2 

 and ultimately nitric acid, while fermentative bacteria reduce the 

 fats and carbohydrates also to COo and OH 2. Much plant 

 substance is also disintegrated in such ways, but the celluloses 

 and perhaps the vegetable oils tend to persist in geological time 

 as peats, lignites, coal and perhaps petroleum. 



37. ON THE INTERDEPENDENCE OF PLANT, ANIMAL 



AND BACTERIAL ORGANISMS 



It is doubtful if plant organisms could continue indefinitely 

 to inhabit an earth physically as it is at present but devoid of 

 animal life. The tendency of plant metabolism is to fix CO 2 

 as fossil remains of the nature of coal, etc., and perhaps in 

 limestone. 



It is certain that animals, constituted as at present, could not 

 continue long to inhabit an earth devoid of plant life. They 

 are unable to utilize inorganic materials as the sources of energy, 

 or of tissue-formation. 



It is certain that very many forms of bacterial organisms can 

 only exist as parasites on living plants and animals, or as 

 saprophytes on plant and animal debris. It is doubtful (but 

 perhaps it is possible) that some exceptional kinds of bacteria 

 could continue to live on an earth physically as at present but 

 devoid of plant and animal life. 



37«. Producers and Consumers. Plants can make use of 

 lifeless materials, building up the inorganic CO 2, OH 2 and 

 inorganic nitrogenous and other salts into their tissue sub- 

 stances — in doing so they arrest the degrading solar radiation 

 and find energy from this that enables them to carry out the 

 chemical transformations noted above. 



