OXYGEN Supply 67 



one-fifth of the air.) The minimum pressure for faculta- 

 tive anaerobes is also mm. Hg. Some experiments have 

 been made to determine the limits for aerobes, but on a few 

 organisms only, so that no general conclusions can be 

 drawn from them. To illustrate: Bacillus subiilis (a com- 

 mon "hay bacillus") will grow at 10 mm. Hg. pressure but 

 not at 5 mm. Hg. It will also grow in compressed oxygen 

 at a pressure of three atmospheres (2280 mm. Hg.), but not 

 at four atmospheres (3040 mm. Hg.), though it is not 

 destroyed. 



Parodko has determined the oxygen limits for five com- 

 mon organisms as follows: 



Minimum. 



Maximum. Vol. Mm. 



In atmospheres. Mm. Hg. per cent. Hg. 



Bacillus fltwrescens . 1.94 to 2.51 1474 to 1908 0.00016=0.0012 



Sarcinalutea . . 2.51to3.18 1908 to 2417 0.00015=0.0011 



Bacillus vulgaris . 3 . 63 to 4 . 35 2749 to 3306 



Bacillus coli . 4.09 to 4. 84 3108 to 3478 



Bacillus prodigiosus . 5.45 to 6.32 3152 to 4800 



These few instances do not disclose any general principles 

 which may be applied either for the growth or for the dis- 

 tinction of aerobes or facultative anaerobes. 



It has been shown that compressed oxygen will kill some 

 bacteria but this method of destroying them has little or 

 no practical value. Oxygen in the form of ozone, O3, is 

 rapidly destructive to bacteria, and this fact is applied prac- 

 tically in the purification of water supplies for certain cities 

 where the ozone is generated by electricity obtained cheaply 

 from water power. The same is true of oxygen in the 

 "nascent state" as illustrated by the use of hypochlorites 

 for the same purpose. 



It was stated (p. 64) that certain thermophil bacteria in 

 the soil have an optimum temperature for growth in the air 

 which is much higher than is ever reached in their natural 

 habitat, and that they grow at a moderate temperature under 

 anaerobic conditions. It has been shown that if these organ- 

 isms are grown with aerobes or facultative anaerobes they 

 thrive at ordinary room temperature. These latter organ- 



