70 BACTERIOLOGY. 



found in the mouth, in a decaying- tooth cavity. It would 

 appear to be somewhat contradictory to find anaerobic 

 bacteria growing- in the soil apparently in the presence of 

 air. Nevertheless, such is the case. The explanation of 

 this curious fact is very simple and can be very easily 

 demonstrated in the laboratory. If, for example, an obli- 

 gative anaerobic germ is planted in beef tea, in the presence 

 of air, it will not develop. If, however, an aerobic germ is 

 planted at the same time as the anaerobe both organisms 

 will develop. It would seem as if the aerobic germ con- 

 sumes the oxygen in the immediate neighborhood of the 

 anaerobe and thus enables the latter to grow. This favor 

 ing action on the part of certain bacteria is known as 

 microbic association, and it is undoubtedly because of such 

 assistance that obligative anaerobic bacteria are able to 

 multiply in the soil. Moreover, it is an association of this 

 kind which enables certain pathogenic members of this 

 group, such as the tetanus bacillus, to develop in the body 

 of animals. 



With but one or two exceptions, all the known obliga- 

 tive anaerobic bacteria are bacilli. An obligative anaerobic 

 micrococcus has been isolated from pus. This group is 

 characterized by the production of large quantities of gas. 

 Moreover, butyric acid is a very common product and may 

 be detected by the odor, not only in the artificial cultures, 

 but at times even in the body of an animal infected with 

 certain organisms of this group. The obligative anaerobic 

 bacteria, therefore, exhibit a marked ability to produce 

 fermentation. 



The methods of cultivating anaerobic bacteria will be 

 described in connection with these organisms, (Chapter XI). 



