ALBUMINOUS MATTERS. 



83 



are preserved in sealed cans, for use upon long voyages or expeditions 

 at a distance from the usual base of supplies. 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 begin to putrefy after the usual interval of time. 



Another essential condition for putrefaction is the presence of 

 moisture. Albuminous substances which are reduced to a perfectly 

 dry state do not undergo decomposition ; and in some regions, where a 

 high temperature and a dry atmosphere favor the rapid desiccation of 

 organic substances, this fact is also utilized for the preservation of 

 meats. Immediately after the animal is killed, the flesh is cut into thin 

 strips and hung up to dry in the air, and, desiccation being completed 

 before putrefaction has commenced, the food thus prepared is preserved 

 for an indefinite time. 



The third requisite for putrefaction is a moderately elevated tempe- 

 rature. It goes on most rapidly between 25 and 35 (^7 to 95 F.). 

 Below 25 it gradually diminishes in activity, and ceases altogether 

 about the freezing point of water. Meats, therefore, which are kept 

 frozen or closely packed in ice do not putrefy. The process is also 

 suspended in all albuminous matters exposed to winter weather at the 

 freezing point. The carcass of an extinct mammoth has even been 

 found imbedded in ice in Northern Siberia, which was in such a state 

 of preservation that its flesh was used for food by dogs and other 

 animals. 1 A temperature much above 35 is also unfavorable to the 

 putrefactive change, and it is completely arrested by a heat approaching 

 that of boiling water. 



The process of putrefaction 

 is accompl ished by the growth 

 and multiplication of a micro- 

 scopic vegetable organism, 

 somewhat analogous to that 

 by which fermentation is ex- 

 cited in saccharine fluids. 

 If any clear solution con- 

 taining animal or vegeta- 

 ble albuminous matters be 

 exposed to the air at a 

 moderate temperature, after 

 a short time it becomes tur- 

 bid. This turbidity is due to 

 the development of minute 

 vegetable cells, of very sim- 

 ple organization, which mul- 

 tiply with great rapidity in 



Fig. 18. 



CELLS OF BACTERIUM TEBMO; from a 

 putrefying infusion. 



1 M6moires de 1' Academic Imperiale des Sciences de St. Petersbourg, tome 5, 

 p. 440. 



