ALBUMENOID SUBSTANCES. 77 



soften, liquefy, and are finally decomposed, with the production of 

 certain fetid gases, among which are hydrogen sulphide and carbide, 

 usually with more or less carbonic acid, nitrogen, and ammonia. These 

 emanations cause an odor which is easily recognized as "putrefac- 

 tive ; " and no substance is capable of putrefaction, unless it contain 

 albumenoid matters among its ingredients. As these matters are 

 more abundant in animals than in vegetables, the phenomena of 

 putrefaction are most distinctly marked in the decay of animal tissues. 

 But they will take place in both, under the requisite conditions. The 

 rapidity of putrefaction in animal substances varies with their con- 

 sistency ; the liquids and the soft parts undergoing this change more 

 readily than those of firmer texture. In some which are exceedingly 

 dense, like the bones, cartilages, hair, and elastic tissues, desiccation 

 may take place before putrefaction can be established; but if their 

 animal matter be extracted in the form of gelatine or otherwise, and 

 kept for a short time in the moist condition, it will putrefy like any 

 other albumenoid substance. 



In order that putrefaction may take place, certain conditions are 

 necessary. In the first place, it requires the access of atmospheric air, 

 or of some fluid containing oxygen. If the putrescible substance be 

 boiled, so as to expel all the free oxygen contained in its fluids, and 

 inclosed in a hermetically sealed vessel, no putrefaction takes place, 

 and the substance remains unaltered indefinitely. It is by this means 

 that cooked meats are preserved in cans, for use upon long voyages 

 or expeditions. So long as the cans are kept perfectly closed, their 

 -contents remain sound. After they are opened and the air admitted to 

 their interior, the food must be used at once, otherwise it will putrefy 

 in a short time. 



Another essential condition for putrefaction is the presence of moist- 

 ure. Albumenoid substances in a perfectly dry state do not undergo 

 decomposition ; and in some regions, where a high temperature and 

 a dry atmosphere favor their rapid desiccation, this fact is utilized for 

 the preservation of meats. Immediately after the animal is killed, the 

 flesh is cut into strips and dried in the air ; and desiccation being thus 

 completed before putrefaction has commenced, the food is preserved for 

 future use. 



The third requisite for putrefaction is a moderately elevated temper- 

 ature. It goes on most rapidly between 25 and 35 C. Below 25 

 it gradually diminishes in activity, and ceases altogether about the 

 freezing point of water. Meats, therefore, which are kept at a suffi- 

 ciently low temperature do not putrefy. The carcass of an extinct 

 mammoth has even been found imbedded in ice in Northern Siberia, 

 in such a state of preservation that its flesh was devoured by dogs 

 and other animals.* A temperature much above 35 is also unfavor- 



* Memoires de 1' Academic Iniperiale des Sciences de St. Petersbourg, tome 5, p. 

 440. 



