162 



PRINCIPLES OF SOIL MICROBIOLOGY 



of oxygen. We do not know of any true anaerobes which grow only in 

 the complete absence of oxygen. Small quantities of free oxygen will 

 even act as stimuli to obligate anaerobes. 



The oxygen need of an organism was characterized 6 by the "cardinal 

 points" for growth and spore formation, namely: minimum, optimum, 

 and maximum, so that there is a gradual transition between aerobes and 

 anaerobes. The following cardinal points for spore formation charac- 

 terize a series of typical bacteria, atmospheric air at 18° and 750 mm. 

 pressure containing 276 mgm. of oxygen per liter: 



Bac. amylobacter. 

 Bac. asterosporus 

 Bac. fusiformis. . 



Bac. mycoides 



Bac. simplex 



Bac. subtilis 



Bac. lactis 



A high maximum does not necessarily correspond to a high minimum. 

 The first generation of anaerobes is more sensitive to oxygen than the 

 following generations, which may even thrive better in the presence of a 

 limited oxygen supply than in its complete absence. 7 This points to 

 adaptation in course of time. Even in the case of a single generation, 

 the organism can withstand greater concentrations of oxygen after the 

 growth of the culture has somewhat advanced than in the beginning. 

 It has been claimed 8 that the growth of even obligate anaerobic bacteria 



6 Meyer, A. Apparat fur die Kultur von anaeroben Bakterien und f tir die 

 Bestimmung der Sauerstoffminima fur Keimung, Wachstum und Sporenbildung 

 der Bakterienspecies. Centrbl. Bakt., II, 15: 337. 1906. Bemerkungen uber 

 Aerobiose und Anaerobiose. Centrbl. Bakt. I, 49: 305 316. 1909; also Ibid. II, 

 15: 1905; 16: 386, 481-488, 577-588, 673-687. 1906. Wund, M. Feststellung der 

 Kardinalpunkte der Sauerstoffkonzentration. Centrbl. Bakt. 42: 97-101, 193- 

 202, 289-296, 385-393. 1906. 



7 Burri, 1907 (p. 161); Kiirsteiner, J. Beitrage zur Untersuchungstechnik 

 obligat anaerober Bakterien, sowie zur Lehre von der Anaerobiose iiberhaupt. 

 Centrbl. Bakt. II, 19: 1-26, 97-115, 202-220, 385-399. 1907; Burri, R. and Kiir- 

 steiner, J. Ein experimentaler Beitrag zur Kenntnis der Bedeutung des Sauer- 

 stoffentzugs f tir die Entwicklung obligat anaerober Bakterien. Ibid. 21: 289- 

 307. 1908; Landw. Jahrb. d. Schweiz. 1909, 422. 



8 Fermi, C, and Bassu, E. Untersuchungen iiber die Anaerobiosis. Centrbl. 

 Bakt. I, 35: 563-568, 714-722. 1905; 38: 138-145, 241-248, 369-380. 1905. 



