Typhus Rickettsiae are found in large numbers in sections of tissue cultures of scrotal sac exudate.

Extensive multiplication of the organisms occurs, and new cells become infected. Organisms are seen in cells undergoing mitotic division.

The organisms usually become less numerous after the 6th day in vitro, but in one instance organisms were extremely numerous on the 16th and 21st days.

Rickettsiae in tissue cultures retain their intracellular location, even when infection is very heavy.

They multiply exclusively in non-phagocytic cells which are believed to be of mesothelial origin.

Pleomorphism is much more pronounced in tissue cultures than in guinea pig tissues and is entirely comparable to that seen in the louse.

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