BACTERIA. 31 



withstand is about the same as that for other vegetative plant- 

 cells, namely, about 50-60 C. Certain Bacteria, e.g. B. tliermo- 

 philus, grow and thrive vigorously at 70 C. Many spores, on the 

 contrary, are able to bear far higher temperatures (in several 

 species a temperature for some duration of above 100, those of 

 Bacillus subtilis, for instance, can withstand for hours a tempera- 

 ture of 100 in nutrient solutions ; the spores remain capable of 

 development after exposure to a dry heat of 123 C.). 



The Desiccation of the air, if prolonged, kills many forms when 

 in the vegetative condition. The spores however can bear a much 

 longer period of dryness, some even several years. 



OXYGEN. Some species cannot live without a supply of free 

 oxygen (Aerobic), e.g. the Vinegar-bacteria, the Hay-bacilli, the 

 Anthrax-bacilli, the Cholera- Microspira. Other species again thrive 

 vigorously without supply of free oxygen, and are even checked in 

 their development by the admission of air (Anaerobic), e.g. the 

 butyric acid Bacterium (Glostridium butyricum = Bacillus amy- 

 lobacter). A distinction may be drawn between obligate and 

 facultative aerobics and obligate and facultative anaerobics. 

 Several Bacteria, producing fermentation, may grow without the 

 aid of oxygen when they are living in a solution in which they 

 can produce fermentation ; but, if this is not the case, they can 

 only grow when a supply of oxygen is available. A great 

 number of the pathogenic Bacteria belong to the facultative 

 anaerobics. 



A luminous Bacterium (Bacillus phosphorescens) which in the 

 presence of a supply of oxygen gives a bluish-white light, has 

 been found in sea- water. Phosphorescent Bacteria have fre- 

 quently been observed upon decaying sea-fish, as well as on the 

 flesh of other animals ; by transferring the Bacteria from cod fish 

 to beef, etc., the latter may be made luminous. 



Organic carbon compounds are indispensable for all Bacteria, 

 (except, as it appears, for the nitrifying organisms), as they can 

 only obtain the necessary supplies of carbon from this source. The 

 supplies of nitrogen, which also they cannot do without, can be ob- 

 tained equally as well from organic compounds as from inorganic 

 salts, such as saltpetre or ammonia-compounds. The various "ash- 

 constituents " are also essential for their nourishment. 



While Moulds and Yeast-Fungi grow best in an acid substratum, 

 the Bacteria, on the other hand, generally thrive best in a neutral 

 or slightly alkaline one. 



