It is already made clear by Nicolle in 1911 that typhus is a louse-borne disease. Rickettsia has not however been found in the salivary glands of louse contrary to the report of Sikora in earlier days. They are grown within the cells of alimentary tract and are, therefore, excreted in abundance in louse-feces. Infection to human body may develop not though spitting in when bitten by the infected louse unless the louse is habitual to vomit during feeding.
Kitaoka has previously described as to the mode of rickettsia infection to human body and it is generally of agreement that when the skin is injured by louse bites and eventually by scratches or even by rubbing, the rickettsia is able to invade the human body and the nasal menbrane and the conjunctiva serve as entry of the infection when infectious materials are inhalated or contaminate the conjunctiva. Furthermore it was pointed out that rickettsia is curving under certain circumstances for the long period as described by Arkwright, Starzyk, Wilcooks, Löffier, Van den Ende and other authors. Then dispersion of infectious louse-feces has become an origin of infection in the epidemiology of typhus. In other words the epidemic typhus is not only a louse-borne disease but also is a air-borne disease and it is to be noted that the typhus case without louse infestation may be infected by rickettsia from such origin.
The present study is to see how long and under what circumstances can the rickettsia contained in the louse-feces survive and be an origin to spread the disease.