ANAEROBTOSIS 



115 



obligate anaerobes are inoculated into broth kept under aerobic conditions, no 

 reduction is effected and the potential remains unchanged at about -j-0-3 v. Lepper 

 and Martin (1929, 1930) have investigated the meat tubes used for the cultivation 

 of anaerobes. The pieces of cooked meat placed in these tubes are able to maintain 

 reducing conditions in such tubes even when the surface of the medium is exposed 

 to air. In fact, an E^ of about — 0-2 volt is established, the effect being ascribed 

 to the autoxidation of lipins and to the reversible oxidation-reduction system : — - 

 parahsematin ^ hsemochromogen. When staphylococci are inoculated into this 

 medium no fall in potential occurs, in agreement with the results quoted above, 

 namely that a minimum level of — 0-2 v. is reached in cultures of staphylococci. 

 But when anaerobic organisms such as B. tetani are introduced into the medium the 

 potfaitial falls to a level of ^0-4 v. or even lower. We find therefore that aerobic 

 organisms are able to reduce ordinary aerobic media to the level E^ — 0-2 volt, 

 whilst anaerobes are unable to reduce ordinary aerobic culture media, but require 

 the medium to be partially reduced before proliferation can commence. In addition 

 some organisms, the facultative anaerobes, are capable of either aerobic or anaerobic 

 growth. 



Time 



Fig. 26 

 Potential-time curve of hypothetical aerobe and anaerobe 



The degree of reduction attained (or potential reached) is not necessarily 

 different for aerobes and anaerobes. Some aerobes, e.g., B. coli, beginning with 

 ordinary aerobic media, are capable of producing the most intense reducing condi- 

 tions, even corresponding to the potential of the normal hydrogen electrode. On 

 the other hand, some anaerobes are incapable of proliferating in ordinary aerobic 

 media, and, even under anaerobic conditions, they are unable to give rise to intense 

 reducing conditions or very low potentials. The distinguishing feature of aerobes 

 and anaerobes, therefore, is not in the potential ultimately reached in the culture, 

 but in the potential range at which they are able to initiate growth. 



Figs. 26 and 27 are intended to illustrate this point of view. Fig. 26 represents 

 the potential : time curve of a hypothetical aerobe and anaerobe. The aerobe is able 

 easily to reduce the medium from the level of potential of ordinary aerobic culture 

 media (E^ about -f- 0-3 v.) to about — 0-2 v. but no lower. The anaerobe, on the 

 other hand, is unable to reduce ordinary aerobic media, but if the medium is subjected 

 to a preliminary partial reduction the anaerobe can continue the reduction and reduce 



