DECAY OF ORGANIC MATTERS. 241 



most readily remarked, is the fetid odor which animal substanceas 

 exhale during putrefaction. It is not always the smell of ammonia 

 which predominates ; that of sulphuretted hydrogen gas is often 

 very strong ; yet that is not the emanation which is most repulsive : 

 miasmata and nauseous principles are also developed which seem to 

 be the changed matter itself carried away by the gases that are dis- 

 engaged. 



Sulphur, like phosphorus, is almost always a constituent of or- 

 ganic bodies ; its minute proportion, however, would be insufficient 

 to give out the hepatic odor so intense as we often find it during 

 putrefaction. The production of sulphuretted hydrogen is connect- 

 ed w^ith the very curious fact, first appreciated by M. O. Henri, 

 that sulphates dissolved in a medium impregnated with azotized 

 matter in decomposition, do themselves undergo an actual reduction, 

 pass into the state of sulphurets, and immediately give out sulphuret- 

 ted hydrogen, either by the action of the carbonic acid of the at 

 mosphere, or by that which is formed during the putrefaction of the 

 organic matter. It is by a similar action exerted upon sulphate of 

 lime that M. Henri explains the origin of the sulphureous waters of 

 Enghien, near Paris ; and M. Fontan in his important work on min- 

 eral waters has generalized this explanation. 



The causes of the destruction of sulphates under such circum- 

 stances is easily understood. During the decomposition of organiz- 

 ed substances, the carbon belonging to them forms carbonic acid gas ; 

 by combining both with the oxygen of the substances themselves, 

 and with the oxygen of the water, it is probable that the oxygen of ' 

 the sulphuric acid contributes equally to this formation, and that the 

 sulphur is liberated. 



The hydrogen of the decomposed water, as well as that of the 

 solid matter, in contact with sulphur in the nascent state, combines 

 with it to form sulphuretted hydrogen, which straightway reacts 

 upon the base of the sulphate, producing from it, as we know, water 

 and a metallic sulphuret. This sulphuret being unable to exist when 

 exposed to the continued disengagement of carbonic acid gas which 

 takes place in the centre of the mass in putrefaction, yields, as a 

 definite result, a carbonate on the one part, and sulphuretted hydro- 

 gen on the other. 



The faculty which azotized organic bodies possess of undergoing 

 spontaneous decomposition in presence of water, and under the in- 

 fluence of heat, seems to depend upon the tendency which azote has 

 to unite with hydrogen in order to form ammonia. 



This tendency is perhaps the determining cause of the phenome- 

 non of fermentation taken in the most general acceptation of the 

 term. Organic bodies void of azote decompose less easily, and the 

 kind of alteration which they undergo from the action of water and 

 air, differs in many respects from the putrefaction of azotized mat- 

 ter. Of this the difficulty experienced in effecting the fermentation 

 of vegetable substances is a proof Nevertheless, the vegetable re- 

 fuse which goes to the dunghill, all without exception, contains azo- 

 tized elements, often, it is true, in extremely minute proportions; 



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