CONDITION OF GROWTH OF THE BACTERIA 15 



from compounds containing oxygen. In the former case 

 they are termed aerobic, in the latter anaerobic. Pasteur, 

 in 1861, first pointed out the fact that certain species of 

 micro-organisms not only grow in the entire absence of 

 oxygen, but that for some no growth can occur in the 

 presence of this gas. The cultivation of ' strict anaerobics ' 

 calls for methods by which oxygen is excluded. 



The ' facultative anaerobics ' grow either in the presence 

 or absence of oxygen. There are various gradations in 

 this regard, from the strictly aerobic species which require 

 an abundance of oxygen, and will not grow in its absence, 

 to the strictly anaerobic, which will not grow if there is a 

 trace of oxygen in the media in which it is proposed to 

 grow them. According to this relation to oxygen they are 

 classed as ' facultative ' and ' obligate ' aerobic or anaerobic 

 bacteria, as the case may be. Among the most interesting 

 pathogenic bacteria which are 'obligate' anaerobics are the 

 bacillus of tetanus, malignant oedema, and symptomatic 

 anthrax. On the other hand, bacteria such as anthrax, for 

 instance, are aerobic, but facultatively so, since they can 

 live for a long time out of contact with oxygen. 



Again, bacteria cannot live and reproduce unless they 

 have a proper temperature. This varies very much with 

 the different organisms, but in most cases is not less than 

 12° C. ( = 54° F.), nor more than 40° C. ( = 104° F.). There 

 are, however, bacteria which can grow at 0° C. ( = 32° P.), 

 and others which can do so at from 60° to 70° 0. ( = 140° to 

 158° F.). These are the 'thermophilic' organisms which 

 have been recently studied by Miquel, McFadyean, and 

 others. 



With regard to the conditions of life of the bacteria, 

 they may be divided broadly into two classes. When the 

 organisms draw their nourishment from some living body 

 or 'host,' they are known as 'parasites.' These are 



