PRODUCTS OF THE GROWTH OF BACTERIA. 121 



simpler compounds. Fermentation refers especially to the 

 formation of useful products like alcohol. The term putre- 

 faction is employed chiefly for the breaking up of nitrogenous 

 compounds with the development of foul-smelling gases. The 

 term fermentation is also applied to the decomposition of com- 

 plex substances through the influence of unorganized ferments 

 or enzymes. The work of bacteria in decomposition is indis- 

 pensable to the existence of the organic world as we find it. 

 Green plants convert the stable compounds of nitrogen, the 

 carbon dioxide of the atmosphere and water into the complex 

 and unstable albumens and carbohydrates which serve as food 

 for animals. Animals, on the other hand, convert these un- 

 stable and complex compounds back into simpler forms. The 

 work of changing them back into the simple and stable con- 

 dition, in which they serve as the food for plants, is performed 

 by animal life in part only, and its completion is left to the 

 activities of bacteria. It is the work of bacteria in this direction 

 which we call decomposition. Without that work the existence 

 of life upon the earth as we understand it would soon come to 

 an end, and the dead and undecomposed bodies of living 

 things and their products of all kinds would lie about unchanged, 

 as they had fallen. 



Bacterium termo is the name formerly given to a supposed 

 species of bacteria which was credited with being the producer 

 of putrefaction. The individuals were represented as being short 

 rods, mostly going in pairs, and actively motile. The term 

 has been abandoned since it appears to have included a number 

 of different species. 



