X-rayed and typhus infected rats presenting a generalized peritoneal infection by rickettsiae show temperature curves which are usually under 38°C.

Guinea pigs and rabbits inoculated with Mexican typhus develop temperature curves which are usually over 39.5°C. Rickettsia bodies may be found in the tunica vaginalis but not in the peritoneal fluid. Treating these animals by X-ray radiation does not favor the growth of rickettsiae in the peritoneal cavity as observed in rats.

When guinea pigs, rabbits and sheep are submitted to reduction of the leucocytes mainly by the X-ray method, then inoculated with Mexican typhus by the peritoneal route and maintenance of the body temperature under 38°C., a generalized rickettsial infection of the peritoneum has been observed.

Rectal temperatures above 38°C. (101.3°F.) are not suitable for the massive growth of Mexican typhus rickettsiae within the serosal cells of the peritoneal cavity.

The possibility of a practical application of these studies to the production of typhus vaccine is now being considered.

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