CHAPTER XXIV. 
THE ANAEROBIC BACTERIA. 
There is a well defined group of bacteria, the members of which 
exliibit in common an inability to grow in pure culture in the presence 
of the air. The discovery of the first member of this group of anaerobic 
bacteria, as well as the demonstration of the phenomenon of an anaer- 
obic existence, was one of the great contributions to bacteriology by 
Louis Pasteur. 
The anaerobic organisms appear to be poisoned by atmospheric 
oxygen, when they are in the vegetative state, but they are able to 
derive their energy from oxygen-rich, non-nitrogenous compounds of 
suitable stereo-configuration, as carbohydrates, without difficulty. 
Nitrogenous compounds, as amino-acids and their complexes, are also 
utilizable as sources of energy. The exact mechanism whereby com- 
bined, but not molecular, oxygen is utilizable by anaerobic microbes is 
not known. 
The majority of anaerobes form highly resistant spores which are 
apparently unaffected by the oxygen of the air; these spores may remain 
viable, when dried, and kept in a cool, dark place, freely exposed to the 
air, for years, and probably even decades in some instances. Obviously 
the spore state is of paramount importance in the preservation of such 
bacteria. 
Anaerobes are found widely distributed in the soil, especially in 
close association with man or mammals. It has been suspected, there- 
fore, that the soil is the natural habitat of the members of this group. 
Available evidence points to the intestinal tract of the mammalia 
as the most probable, or at least the most important, anaerobic incu- 
bator, because the conditions within the alimentary canal are favorable 
for the theoretical requirements of this group both with respect to the 
absence of molecular oxygen, and the presence of a very favorable 
nutritive environment. Sporulation takes place in the alimentary 
canal under ordinary conditions, provided the acidity therein is minimal, 
and the organisms therefore leave the intestinal environment, in part 
at least, in such a state as to survive successfully prolonged exposure 
to unfavorable conditions. Not all bacteria, however, which are 
anaerobic, are found in the intestinal tract. B. botulinus, a toxicogenic 
member of the group, is said to develop poorly or not at all, at the 
temperature of the mammalian body (38° C). Certain members of the 
group of the Spirochseta are anaerobic, and so far as is known, do not 
produce spores, nor do they live in the alimentary canal. The spiral 
