OF BODIES DESTITUTE OF NITROGEN. 303 



filled with mercury, 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 therefore neces- 

 sary to cause its fermentation, still this change did not ensue 

 when the juice was heated in close vessels to the temperature of 

 boiling water. When thus, treated, it could be preserved for 

 years without losing its property of fermenting. A fresh expo- 

 sure to the air at any period caused it to ferment. 



Animal food of every kind, and even the most delicate vege- 

 tables, may be preserved unchanged if heated to the temperature 

 of boiling water in vessels from which the air is completely ex- 

 cluded. Food thus prepared has been kept for fifteen years, and 

 upon opening the vessels after this long time, has been found as 

 fresh and well-flavored as when originally placed in them. 



The action of the oxygen in these processes of decomposition 

 is very simple ; it excites changes in the composition of the 

 azotized matters dissolved in the juices ; — the mode of combina- 

 tion of the elements of those matters undergoes a disturbance 

 and change in consequence of their contact with oxygen. The 

 oxygen acts here in a similar manner to the friction or motion 

 which effects the mutual decomposition of two salts, the crystalli- 

 zation 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 parti- 

 cle of an azotized body in this act of decomposition exercises an 

 influence upon the particles in contact with it, and the state of 

 motion is thus propagated through the substance. The air may 

 now be completely excluded, but the fermentation or putrefaction 

 proceeds uninterruptedly to its completion. 



Aldehyde attracts oxygen from the air, and, by the process of 

 eremacausis, becomes vinegar ; if the air be now excluded, the 

 disturbance already begun is not arrested, but the products are 

 very different. Two substances are then formed by a change in 



