ANAEROBIC BACTEEIA 105 



This experiment clearly shows that the optimum growth of anaerobic 

 bacteria is secured, not when oxygen is absent altogether, but rather 

 when a very small amount of it is present, the optimum amount being 

 different for the different bacteria. This dictum is applicable to both 

 obligate and facultative anaerobes. Beijerinck also showed that when 

 an anaerobic bacillus is placed in a drop of water the individuals collect, 

 not at a point furthest removed from the surface, but at another poinf> 

 where the oxygen present is such as best suits the needs of that 

 particular bacillus. In consequence of these results he has proposed 

 substituting the words aerophile and microaerophile for aerobic and 

 anaerobic respectively. 



The researches of Chudjakow have also produced important results. 

 He proved beyond question that under atmospheric conditions the 

 oxygen of the air acts directly as a poison to non-sporogenous anaerobic 

 bacteria, and if not removed in time its influence causes the death of 

 the anaerobe exposed to it. In the case of a spore-forming culture 

 the spores are not destroyed by oxygen, though they are rendered 

 incapable of germination. But if the amount of oxygen be gradually 

 reduced, a point is reached at which the oxygen not only exerts no 

 harmful effect, but is actually helpful. This applies to all anaerobes, 

 they thrive better when a little oxygen is present than when this gas 

 is altogether excluded ; and when growing under such a condition, all 

 the oxygen is used up just as it is by aerobic organisms. Before this 

 can take place, however, the oxygen must be present in a very dilute 

 condition. Thus for Bactridium butyricum the amount of oxygen 

 supplied to it must not be greater than what corresponds to 5 mm. of 

 air-pressure. But an amount of oxygen equal to 10 or 15 mm. of 

 air-pressure acts injuriously on this organism, and ultimately results 

 in its death. Similar results are obtained with other anaerobes. Of 

 course, the maximum amount of oxygen that any individual anaerobe 

 can tolerate without injury varies in each case. Whilst for Bactridium 

 butyricum the maximum is 5 mm., for Bacillus oedematis it reaches 

 as high as 25 mm., and for Clostridium butyricum about 10-12 mm. 

 We therefore come to the important conclusion that the strictest of 

 anaerobes can make use of oxygen provided this gas be supplied in a 

 sufficiently dilute condition. 



In recent years a closer study of the aerobic microorganisms has 

 shown that they also are not unaffected by the amount of oxygen that 

 is present. Thus Bacillus subtilis was rapidly killed when subjected 

 to a pressure of oxygen equal to 10-15 atmospheres. For other 

 organisms, again, very little oxygen suffices for their needs; thus 



