Vill. 
ACTION OF GASES AND OF THE HALOID ELEMENTS 
UPON BACTERIA. 
Oxygen.—Free oxygen is essential for the development of a large 
number of species of bacteria—aérobics ; and it completely prevents 
the growth of others—anaérobics. Many bacteria, even when freely 
exposed in a desiccated condition to the action of atmospheric oxygen, 
retain their vitality for along time. The gradual loss of pathogenic 
power which Pasteur has shown occurs in cultures of the anthrax 
bacillus and the micrococcus of fowl cholera, is ascribed by him to 
exposure to oxygen, and as proof of this he states that cultures kept 
in hermetically sealed tubes do not lose their virulence in the same 
degree. But other circumstances may influence the result. Thus 
some of the products of growth which accumulate in culture fluids 
have an injurious effect upon the vitality of the bacteria which pro- 
duced them, and in time may cause a complete destruction of vitality. 
In cultures exposed to the air these products would be in a more 
concentrated solution from the gradual evaporation of the culture 
liquid. It must also be remembered that light in the presence of 
oxygen is a germicidal agent. 
The experiments of Friinkel show that the aérobic bacteria grow 
abundantly in the presence of pure oxygen, and some species even 
more so than in ordinary air. Micrococcus prodigiosus, however, 
appeared to be unfavorably affected by pure oxygen, inasmuch as it 
did not produce pigment so readily as when cultivated in ordinary air. 
Nascent oxygen is a very potent germicidal agent, as will be seen 
in our account of such oxidizing disinfectants as potassium perman- 
ganate and the hypochlorite of lime. 
Ozone.—It was formerly supposed that ozone would prove to be 
a most valuable agent for disinfecting purposes ; but recent experi- 
ments show that it is not so active a germicide as was anticipated, 
and that from a practical point of view it has comparatively little 
value. 
Lukaschewitsch found that one gramme in the space of a cubic 
metre failed to kill anthrax spores in twenty-four hours. The cholera 
spirillum in a moist state was killed in this time by the same amount, 
but fifteen hours’ exposure failed to destroy it. Ozone for these ex- 
periments was developed by means of electricity. 
