142 BACTERIOLOGY. 
in thé amount of oxygen admitted, and many, indeed, 
grow equally luxuriantly in the partial exclusion of 
oxygen. Life in the animal hody, for example, as in 
the intestines, necessitates existence with diminished 
supply of oxygen. Pigment formation almost always 
ceases with the exclusion of oxygen, but poisonous 
products of decomposition are more abundantly pro- 
duced (Hueppe). 
It is important to note that, according to recent in- 
vestigations, it has been shown that the aérobic devel- 
opment of the anaérobes may be facilitated by the pres- 
ence of living or dead aérobes. 
It has also been observed not infrequently that certain 
species which on their isolation at first showed more or 
less anaérobic development—that is, a preference to grow 
in the depth of an agar stick culture, for instance— 
after a while seem to become strict aérobes, growing 
only on the surface of the medium. This observation 
proves that the simple fact of an organism showing 
aérobic for anaérobic growth is not sufficient for its 
separation into a distinct species. 
While all facultative as well as strict anaérobes grow 
well in nitrogen and hydrogen, they behave very differ- 
ently toward carbonic acid gas. A large number of 
these species do not grow at all, being completely in- 
hibited in their development until oxygen is again 
admitted—for example, B. anthracis and B. subtilis 
and other allied species. It has been found in some 
species, as glanders and cholera, that the majority of 
the organisms are quickly killed by CO,, while a few 
offer a great resistance, rendering impossible complete 
sterilization by means of this gas. Another group, 
again—viz., streptococcus and staphylococcus—exhibits 
