42 CONDITIONS OF BACTERIAL LIFE. 



class belong Bacillus oedematis maligni, Bac. tetani, Bac. 

 chauvoei (symptomatic anthrax), and numerous inhab- 

 itants of mud and soil. Upon exposure to free atmos- 

 pheric oxygen, the vegetative forms of these bacteria die 

 in one or more hours ; the spores, on the contrary, are 

 more resistant to oxygen. (Compare Chudiakow, C. B. L. 

 iv, 389. ) Since the principal source of energy is excluded 

 from the anaerobes which is at the command of aerobic 

 bacteria (oxidation of the absorbed nutrient material by 

 means of free oxygen), they are assigned to nutrient mate- 

 rials which are readily utilized, — as, for example, grape- 

 sugar, — which liberate energy (heat) by division into two 

 smaller molecules (for example, alcohol and C0 2 , or acetic 

 acid, or lactic acid). Therefore anaerobes are often grown 

 upon gelatin or agar containing \°/ to 2% of glucose. 

 Upon such media the virulence and also the ability to 

 produce spores suffer, so that recently sodium sulphid 

 (compare p. 43) and formate of sodium have been em- 

 ployed as additions to the culture media. 



III. Facultative aerobes and facultative anaerobes. 1 

 The great majority of the bacteria usually grown by us 

 aerobically — including almost all pathogenic forms — will 

 tolerate a limitation in the amount of oxygen admitted 

 without being injured, moreover without interference with 

 their growth. This is favorable to a life in many parts of 

 the animal body; for example, in the intestinal canal, where 

 oxygen is limited or absent. Chromogenesis is almost 

 always suspended by the exclusion of oxygen; on the con- 

 trary, toxic metabolic products are sometimes abundantly 

 elaborated in its absence (Huppe). 



It is very important, as recent inquiry has shown, that 

 aerobic varieties of the anaerobic .bacteria also exist. Their 



still grew with an air pressure of 5 mm. ; three of the best-known 

 anaerobes he found still able to grow with the barometer at 20 to 

 40 mm. (C. B. L. IV, 389). 



1 As emphasized by Beijerinck, it would be better to speak of "tem- 

 porary ' ' anaerobic varieties, if it has not been demonstrated that cer- 

 tain varieties can grow permanently as well aerobically as anaerobically 

 (C. B. L. in, 40). The demonstration produced by Pfeffer is also 

 interesting, that many aerobic bacteria can bind loosely considerable 

 amounts of oxygen, which they gradually release in spaces free from 

 oxygen (C. B. L. II, 763). 



