THE CHEMISTEY OF BACTERIA. 93- 



The following- terms are frequently employed in this con- 

 nection: 



Zymogenic, or fermentation bacteria, 

 Saprog-enic, or putrefaction bacteria, 

 Chromogenic, or pigment bacteria, 

 Aerogenic, or gas producing bacteria (p. 91), 

 Photogenic, or light producing, phosphorescing- 



bacteria, 

 Toxicogenic, or poison producing bacteria. 

 Pathogenic, or disease producing bacteria. 



It must not be supposed from the above grouping" of 

 bacteria that a giv^n species is necessarily confined or lim- 

 ited to one or the other of these groups. It should be re- 

 membered that the work done by a given organism depends 

 upon the medium and on the surrounding conditions, or 

 environment. A given species may produce a typical fer- 

 mentation when grown in a medium containing sugar, and, 

 when transplanted to albuminous material it may cause an 

 equally typical putrefaction. Moreover, the same organism 

 may produce gas, or when introduced into the animal body 

 may give rise to disease. The above terms, therefore, are to 

 be taken as referring to the most pronounced action or 

 function exhibited by an organism under certain conditions. 



Fermentations. 



The change brought about by an organized ferment (bac- 

 teria, yeasts, moulds, etc.), whereby complex organic bodies 

 are broken up into relatively simpler compounds, may be 

 designated as a fermentation. It is evident, therefore, that 

 fermentations are vital phenomena, the result of the activ- 

 ity oLmicro-organisms. Prom what has been said hereto- 

 fore, it is clear that these organisms induce fermentative 



