The results of the foregoing experiments show that the typhus virus, found in the blood of guinea pigs during the height of typical experimental typhus fever, does not survive at 37°C. in anaerobic media for as long a period as in the same media under aerobic conditions. In media from which oxygen is excluded, the viability period is 24 to 48 hours; in the same media having no barrier to atmospheric oxygen, the period is usually 5 days, in one instance, 3 days.

The dead virus fails to induce not only the typical experimental disease but also an immunity to further injections of typhus virus.

That the death of the virus is due to exclusion of oxygen from the medium, rather than to a change in the hydrogen ion concentration therein is inferred from the fact that media with varying hydrogen ion concentrations, such as broth (pH 7.4), horse serum (pH 7.8), and human ascitic fluid (pH 8.0) have the same comparative effect on the virus, when under aerobic and anaerobic conditions. That is, in all, the anaerobic state causes a shortening of the viability period of the typhus virus.

In the Smith-Noguchi tissue, ascitic fluid, sealed medium in which bacteria resembling Plotz' bacilli grow luxuriantly and remain viable for several weeks, the typhus virus does not increase in virulence, and even dies after 24 hours. This evidence supports the conclusion previously presented that the Bacillus typhi exanthematici of Plotz is not identical with the active agent of typhus virus.

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