EREMACAUSIS, OR DECAY. 295 



CHAPTER VI. 



Eremacausis, or Decay. 



In organic nature, besides the processes of decomposition named 

 fermentation and putrefaction, another and not less striking class 

 of changes occurs, which bodies suffer from the influence of the 

 air. This is the act of gradual combination of the combus- 

 tible elements of a body with the oxygen of the air ; a slow 

 combustion or oxidation, to which we shall apply the term of 

 eremacausis. 



The conversion of wood into humus, the formation of acetic 

 acid out of alcohol, nitrification, and numerous other processes, 

 are of this nature. Vegetable juices of every kind, parts of ani- 

 mal and vegetable substances, moist sawdust, blood, &c, cannot, 

 be exposed to the air, without suffering immediately a progressive 

 change of color and properties, during which oxygen is absorbed. 

 These changes do not take place when water is excluded, or when 

 the substances are exposed to the temperature of 32°, and it has 

 been observed that different bodies require different degrees of 

 heat, in order to effect the absorption of oxygen, and, conse- 

 quently, their eremacausis. The tendency to undergo this 

 change is possessed in the highest degree by substances contain- 

 ing nitrogen. 



When vegetable juices are evaporated by a gentle heat in the 

 air, a brown or brownish-black substance is precipitated as a pro- 

 duct of the action of oxygen upon them. This substance, which 

 appears to possess similar properties from whatever juice it is ob- 

 tained, has received the name of extractive matter ; it is insoluble 

 or very sparingly soluble in water, but is dissolved with facility 

 by alkalies. By the action of air on solid animal or vegetable 

 matters, a similar pulverulent brown substance is formed, and is 

 known by the name of humus. 



