46 Biology of Bacteria 



found it possible to produce a tolerance to a certain amount 

 of bichlorid of mercury by cultivating Friedlander's bacillus 

 upon culture media containing gradually increasing amounts 

 of the salt, until from 1-15,000 which inhibit ordinary cul- 

 tures, it could accommodate itself to 1-2000. 



A thorough knowledge of the biology of bacteria and the 

 conditions prejudicial to their life is of great practical im- 

 portance in enabling one to carry out intelligently clinical 

 precautions such as the sterilization of instruments, surgical 

 dressings, etc., and use sufficiently radical measures for the 

 disinfection of the skin to be incised, as well as of the 

 hands of the operator. 



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. 



