THE CHEMISTEY OF BACTEBIA. 121 



perature in the interior of the mass rises and, in a day or 

 two, may reach 50° or more. As a result of this fermenta- 

 tion a special flavor or aroma is imparted to the tobacco. 

 Inasmuch as this fermentation is due to certain bacteria, it 

 has been proposed to utilize pure cultures of certain of 

 these organisms in order to obtain good grades out of 

 otherwise poor material. In the preparation of snuff, 

 the tobacco is, likewise, subjected to a fermentation, in. 

 which the temperature rises even higher than mentioned 

 above. 



In the preparation of sauer-kraut, fermented hay, and 

 ensilage, similar phenomena take place. The material is 

 thoroughly stamped, or compressed, in large masses, and 

 allowed to ferment. Not infrequently, thetemperature on 

 the inside, will rise to 70°. The material becomes acid, due 

 largely to the presence of lactic, and butyric acids. At the 

 same time it becomes soft, and acquires a more or less, 

 characteristic, not unpleasant odor. 



The high temperature which develops in the interior 

 of large masses of green hay, may, if air is suddenly admit- 

 ted, lead to spontaneous combustion. This may also occur 

 with masses of moist cotton, and the fires in cotton laden 

 ships are not, infrequently, due to such causes. 



Toxipogenic and Pathogenic Bacteria. 



In fermentation and putrefaction, more or less com- 

 plex, dead animal and vegetable substances are acted upon, 

 by diverse organisms, such as bacteria, moulds and yeasts. 

 They are transformed into relatively simpler compounds, 

 and eventually into inorganic forms, such as carbonic acid,, 

 ammonia, nitrites, nitrates, sulphates, phosphates, etc., 

 which, as shown heretofore, are then utilizable by living 

 plants. Hence, lifeless remains are indispensable to new 

 life, and, the micro-organisms which accomplish this 



