I 



CHAPTER XXIII 

 DECOMPOSITION 



The Disposal of Organic Wastes. — The syntheses 

 which are carried on by plants in their own bodies, and 

 the metabolic changes in the bodies of animals, produce, 

 among other things, insoluble substances which, because 

 they are insoluble, are of no immediate use to the plant 

 or animal after they cease to be parts of the living 

 mechanism, that is, after they are excreted or after the 

 organism dies. These matters would accumulate and 

 cumber the earth if they. were not removed. Removal 

 is accompHshed by the slow processes of ^'weathering" 

 and by decomposition, chiefly fermentation, and putre- 

 faction. Weathering consists in the operation of inani- 

 mate influences, the action of the oxygen of the air, of 

 light, heat, frost, water, wind, drying, etc. The other 

 processes are carried on by living things, mainly micro- 

 organisms, which operate by means of the enzyms already 

 referred to in Chapter VII. 



Decomposition. — Fermentation and putrefaction are 

 particular forms of decomposition, the products of which 

 often distinguish them. Thus alcohol and the offensive 

 odors of decay mark respectively a certain fermentation, 

 namely alcoholic, and certain putrefactions. In all these 

 cases there are energy changes and changes in chemical 

 composition. Decay which takes place with offensive 

 odors is called putrefaction. Some forms of disease (e.g., 

 gas-gangrene) are actually fermentations or putrefactions. 

 The changes which are termed decay, fermentation, pu- 

 trefaction, decomposition, and those which are the actual 

 cause of disease, are fundamentally alike. Some of the 



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