532 



BIOLOGY OF THE MICRO-ORGANISMS. 



Obligatory 

 anaerobes. 



Facultative 

 anaerobes. 



bacteria into three groups, which differ in an important 

 manner as regards their necessity for oxygen. In 

 the first place, we have a group of what may be 

 termed " obligatory anaerobes," which only grow when 

 the oxygen is removed as completely as possible from 

 the nutrient medium, at any rate when it can be no 

 longer demonstrated by the ordinary chemical means. 

 To this group belong, for example, the bacilli of malig- 

 nant redema, bacillus butyricus, bacillus muscoides, 

 bacillus polypiformis, &c. Some of these organisms 

 have the property of exciting fermentation in certain 

 fermentescible materials, and then they are able to 

 multiply in large numbers in correspondence with the 

 intensity of the fermentation. In the case of other 

 species no fermentative activity has as yet been made 

 out. The fermentations set up by these anaerobic 

 organisms can be arrested by the admission of oxygen, 

 just as is the case with the growth of the same organisms 

 in non-fermentescible substrata. 



A second group is formed by what we may term the 

 " facultative anaerobes." These bacteria grow best and 

 most quickly when the entrance of air is permitted, but 

 they are also capable of developing slowly when air 

 is excluded. The degree to which the growth is in- 

 fluenced by the exclusion of oxygen varies very much in 

 the different species. On the whole an artificial increase 

 in the tension of the oxygen is injurious to the bacteria 

 belonging to this group ; but here also the degree of 

 sensitiveness varies in the different species. Among the 

 very numerous organisms which belong to this group 

 we may mention more especially the various pathogenic 

 organisms, for example, staphylococcus, streptococcus, 

 bacillus septicus cunic., bacillus sept, crassus, bacillus 

 anthracis, bacillus typhi. abdom., bacillus pneumonia?, 

 spirillum cholerse asiatica?. In this group also the 

 majority of the bacteria do not require to exercise fer- 

 mentative activity in order to live without oxygen. In 

 many of them their behaviour, when fermentescible 

 materials are absent, has not as yet been tested ; never- 

 theless simultaneous fermentative activity favours the 



