EREMACAUSIS OR DECAY. 



101 



ously into fermentation and putrefaction, do 

 not in reality suffer those changes without 

 some previous disturbance in the attraction 

 of their elements. Eremacausis always pre- 

 cedes fermentation and putrefaction, and it 

 is not until after the absorption of a certain 

 quantity of oxygen that the signs of a trans- 

 formation in the interior of the substances 

 show themselves. 



It is a very general error to suppose that 

 organic substances have the power of un- 

 dergoing change spontaneously, without the 

 aid of an external cause. When they are 

 not in a state of change, it is necessary, be- 

 fore they can assume that state, that the 

 existing equilibrium of their elements should 

 be disturbed ; and the most common cause 

 of this disturbance is undoubtedly the atmo- 

 sphere which surrounds all bodies. 



The juices of the fruit or other part of a 

 plant which very readily undergo decompo- 

 sition, retain their properties unchanged as 

 long as they are protected from immediate 

 contact with the air, that is, as long as the 

 cells or organs in which they are contained 

 resist the influence of the air. It is not 

 until after the juices have been exposed to 

 the air, and have absorbed a certain quan- 

 tity of cxygen, that the substances dissolved 

 in them begin to be decomposed. 



The beautiful experiments of Gay-Lussac 

 upon the fermentation of the juice of grapes, 

 as well as the important practical improve- 

 ments to which they have led, are the best 

 proofs that the atmosphere possesses an in- 

 fluence upon the changes of organic sub- 

 stances. The juice of grapes which were 

 expressed under a receiver filled with mer- 

 cury, so that air was completely excluded, 

 did not ferment. But when the smallest 

 portion of air was introduced, a certain 

 quantity of oxygen became absorbed, and 

 fermentation immediately began. Although 

 the juice was expressed from the grapes in 

 contact with air, under the conditions there- 

 fore necessary to cause its fermentation, still 

 this change did not ensue when the juice 

 was heated in close vessels to the tempera- 

 ture of boiling water. When thus treated, 

 it could be preserved for years without 

 losing its property of fermenting. A fresh 

 exposure to the air at any period caused it 

 to ferment. 



Animal food of every kind, and even the 

 most delicate vegetables, may be preserved 

 unchanged if heated to the temperature of 

 boiling water in vessels from which the air 

 is completely excluded. Food thus pre- 

 pared has been kept for fifteen years, and 

 upon opening the vessels after this long 

 time, has been found as fresh and well-fla- 

 voured as when originally placed in them. 



The action of the oxygen in these pro- 

 cesses of decomposition is very simple ; it 

 excites changes in the composition of the 

 azotised matters dissolved in the juices; 

 the mode of combination of the elements of 

 those matters undergoes a disturbance and 

 change in conse \uence of their contac with 



| oxygen. The oxygen acts here m a similar 

 ! manner to the friction or motion which af- 

 fects the mutual decomposition of two salts, 

 the crystallization of salts from their solution, 

 or the explosion of fulminating mercury. It 

 causes the state of rest to be converted into 

 a state of motion. 



When this condition of intestine motion 

 is once excited, the presence of oxygen is 

 no longer necessary. The smallest particle 

 of an azotised body in this act of decompo- 

 sition exercises an influence upon the parti- 

 ticles in contact with it, and the state of 

 motion is thus propagated through the sub- 

 stance. The air may now be completely 

 excluded, but the fermentation or putrefac- 

 tion proceeds uninterruptedly to its comple- 

 tion. It has been remarked that the mere 

 contact of carbonic acid is sufficient to pro- 

 duce fermentation in the juices of several 

 fruits. 



The contact of ammonia and alkalies in 

 general may be mentioned amongst the 

 chemical conditions which determine the 

 commencement of eremacausis ; for their 

 presence causes many substances to absorb 

 oxygen and to decay, in which neither oxy- 

 gen nor alkalies alone produce that change. 



Thus alcohol does not combine with the 

 oxygen of the air at common temperatures. 

 But a solution of potash in alcohol absorbs 

 oxygen with much rapidity, and acquires a 

 brown colour. The alcohol is found after a 

 short time 10 contain acetic acid, formic acid, 

 and the products of the decomposition of 

 aldehyde by alkalies, including aldehyde 

 resin, which gives the liquid a brown colour. 



The most general condition for the pro- 

 duction of eremacausis in organic matter is 

 contact with a body already in the state of 

 eremacausis or putrefaction. We have here 

 an instance of true contagion; for the com- 

 munication of the state of combustion is in 

 reality the effect of the contact. 



It is decaying wood which causes fresh 

 wood around it to assume the same condi- 

 tion, and it is the very finely divided woody 

 fibre in the act of decay which in moistened 

 gall-nuts converts the tannic acid with such 

 rapidity into gallic acid. 



A most remarkable and decided example 

 of this induction of combustion has been 

 observed by De Saussure. It has already 

 been mentioned, that moist woody fibre, 

 cotton, silk, or vegetable mould, in the act 

 of fermentation or putrefaction, converts 

 oxygen gas which may surround it into car- 

 bonic acid, without change of volume. New, 

 De Saussure added a certain quantity of hy- 

 drogen gas to the oxygen, and observed a 

 diminution in volume immediately after the 

 addition. A part of the hydrogen gras had 

 disappeared, and along with it a portion of 

 the oxygen, but a corresponding quantity 

 of carbonic acid gas had not been formed. 

 The hydrogen and oxygen had disappeared 

 in exactly the same proportion as that in 

 which they combine to form water; a true 

 combustion of the hydrogen, therefore, had 



