:« ON THE ORIGIN AND ACTION OF HUMUS. 



CHAPTER HI. 



On the Origin and Action of Humus. 



It will be shown in the second part of this work, that all plants 

 and vegetable structures undergo two processes of decomposition 

 after death. One of these is named fermentation, or putrefaction ; 

 the other decay or eremacausis.* 



It will likewise be shown, that decay is a slow process of com- 

 bustion, — a process, therefore, in which the combustible parts of' 

 a plant unite with the oxygen of the atmosphere. 



The decay of woody fibre (the principal constituent of all 

 plants) is accompanied by a phenomenon of a peculiar kind. 

 This substance, in contact with air or oxygen gas, converts the 

 latter into an equal volume of carbonic acid, and its decay ceases 

 upon the disappearance of the oxygen. If the carbonic acid be 

 removed, and oxygen replaced, its decay recommences, that is, 

 it again converts oxygen into carbonic acid. Woody fibre con- 

 sists of carbon and the elements of water ; and if we judge only 

 from the products formed during its decomposition, and from 

 those formed by pure charcoal, burned at a high temperature, 

 we might conclude that the causes were the same in both : the 

 decay of woody fibre proceeds, therefore, as if no hydrogen or 

 oxygen entered into its composition. 



A very long time is required for the completion of this process 

 of combustion, and the presence of water is necessary for its 

 maintenance : alkalies promote it, but acids retard it ; all anti- 

 septic substances, such as sulphurous acid, the mercurial salts, 

 empyreumatic oils, &c, cause its complete cessation. 



* The word eremacausis was proposed by the author some time since, 

 in order to explain the true nature of decay ; it is compounded from 

 i/f*>«, by degrees, and xaveis, burning. 



