RELATION TO ENMRONMENT CLASSIFICATION 29 



or toward an oxygenated area, were able to demonstrate delicately 

 graded variations between species, favoring various degrees of 

 oxygen pressure. 



The discovery by Pasteur that certain bacteria develop only in 

 the absence of free oxygen, produced a revolution in our conceptions 

 of metabolic processes, since up to that time it was believed that life 

 could be supported only when a free supply of O 2 was obtainable. 



r eur's original explanation for this phenomenon was that anae- 

 robic conditions of life were always associated with some form of 

 carbohydrate fermentation and that oxygen was obtained by these 

 microorganisms by a splitting of carbohydrates. As a matter of 

 fact, for a large number of microorganisms, this is actually true, and 

 the presence of readily fermentable carbohydrates not only increases 

 the growth energy of a large number of anaerobic bacteria, but in 

 many cases permits otherwise purely aerobic bacteria to thrive under 

 anaerobic conditions. 6 On the other hand, the basis of anaerobic 

 growth can not always be found in the fermentation of carbo- 

 hydrates or in the simple process of reduction. A number of strictly 

 anaerobic bacteria may develop in the entire absence of carbohy- 

 drates or reducing substances, obtaining their oxygen supply from 

 other suitable sources, some of which may be the complex proteins. 

 Thus the tetanus bacillus may 7 thrive when the nutritive substances 

 in the media are entirely protein in nature. 



The favorable influence of certain actively reducing bodies, like 

 sodium formate or sodium-indigo-sulphate, upon anaerobic cultiva- 

 tion is probably referable to their ability to remove free oxygen from 

 the media and thus perfect the anaerobiosis. 8 



Til like plants which derive much of their energy for growth 

 from the sun's rays, bacteria, with the exception of the pigmented 

 sulphur bacteria, are dependent upon their food supply as a source 

 of energy. To some extent a simple oxidation of carbohydrates and 

 other substances takes place by means of atmospheric oxygen with 

 the production of CO 2 . There is thus a type of true respiration in 

 bacteria with the absorption of oxygen and elimination of CO 2 . Not 

 all the absorbed oxygen reappears as CO 2 and most of the remainder 

 is probably used up in the formation of water or goes into the struc- 

 ture of the bacterial cell. The production of CO 2 has also been 



Theobald Smith, Cent. f. Bakt., I, xviii, 1895. 

 1 Chudiokow, Cent, f . Bakt., Kef., II, iv, 1898. 

 KUasato and Weyl, Zeit. f. Hyg., viii, 1890. 



