ur THE 



UNIVERSITY 



OF 



Fermentation 47 



CONSEQUENCES OF MICRO-ORGANISMAL ENERGY. 

 According to their activities, bacteria are described as 



Zymogens, or bacteria of fermentation. 



Saprogens, or bacteria of putrefaction. 



Chromogens, or color producers. 



Photogens, or phosphorescent bacteria. 



Aerogens, or gas producers. 



Pathogens, or disease producers. 



The vital activities of bacteria occasion many well-known 

 changes in nature. Thus, it is through their energies that 

 by fermentative and putrefactive changes organic matter is 

 gradually transformed from complex to simple compounds. 

 It is by the energy of bacteria that foul waters are gradu- 

 ally purified, and while it is true that the presence of large 

 numbers of bacteria in water detracts from its potability, 

 the very bacteria that cause its condemnation ultimately 

 effect its purification by exhausting the organic matter it 

 contains in their own nutrition. In the modern treatment 

 of sewage by the "septic tank" method, the organic matter 

 contained in the water is consumed through the agency 

 of anaerobic and aerobic bacteria, until its consumption 

 leaves the water once more clear and pure, the no longer 

 useful bacteria dying out as the nutrition becomes exhausted. 

 The promptness with which bacteria attack organic 

 matter is seen in the changes brought about in foods, 

 some of which are ruined in flavor or quality, though others 

 are thought to be improved. Thus, the flavor of butter, 

 sausage, and cheese, the aroma of wines, and many other 

 important gustatory characteristics of our foods depend 

 solely upon the activity of bacteria or other micro-organisms. 

 Many of these activities are harmless, and indeed ad- 

 vantageous, though the fact that they are not infre- 

 quently accompanied by chemic changes, some of which 

 are poisonous, makes it necessary to watch and time their 

 operations lest acridity, acidity, insipidity, or toxicity of 

 the food replace the desired effect. 



Briefly considered, the best known phenomena resulting 

 from bacterial energy are as follows: 



Fermentation. Fermentation is a chemic transforma- 

 tion of carbohydrates resulting from the activity of micro- 

 organisms. The alcoholic fermentation, which is a familiar 

 phenomenon to the layman as well as to the brewer and 



