88 LABORATORY BACTERIOLOGY 
EXERCISE XXXIV 
CULTURES OF ANAEROBIC BACTERIA 
133. Certain bacteria will not grow in the presence of oxy- 
gen (atmosphere), and consequently they must be cultivated 
in a medium from which the air has been expelled, or in the 
presence of some natural gas, such as hydrogen. While cer- 
tain bacteria, like those of symptomatic anthrax, tetanus, and 
malignant cedema, require the absence of oxygen, others, like 
B. subtilis, will not multiply without it. There are, however, 
a large number of bacteria which are able to multiply independ- 
ently of the presence or absence of this element. In reference 
to oxygen requirements bacteria are grouped as follows : 
Obligative aérobic bacteria require oxygen. 
Obligative anaérobic bacteria require the absence of oxygen. 
Facultative aérobic bacteria grow best in the absence of 
oxygen, but will grow in the presence of air. 
Facultative anaérobic bacteria grow best in the presence of 
oxygen, but will grow in its absence. 
There are several methods of cultivating anaérobic bacteria, 
but as a rule they are difficult and cannot be easily handled in 
an elementary course. Two of the simpler processes, however, 
will be tried. 
134. Work for this exercise. Examine and carefully de- 
scribe the appearance of the anaérobic cultures made in Exer- 
cise XXXIII. 
With the wire loop remove one of the colonies from the 
depth of the agar culture and examine it microscopically (1) 
in a hanging-drop preparation and (2) in a stained cover-glass 
preparation. Stain with carbol fuchsin. Examine microscop- 
ically in similar preparations the bacteria from one of the 
fermentation tubes ; describe their appearance in each prepa- 
ration and make a drawing of a few of them. 
