Abstract
In these experiments tissues from infected adult guinea pigs were grown in plasma obtained from normal guinea pigs. With Rocky Mountain spotted fever the bits of tissue were taken from the tunica of the testes. With typhus the cerebral cortex was used. The plasma was obtained from adult normal guinea pigs by centrifuging chilled blood collected in paraffined tubes.
Our results with spotted fever prove that the virus survives and multiplies in such cultures. Evidence of survival of the virus was obtained by causing the disease in guinea pigs by injecting the cultures intraperitoneally. Although the spotted fever reaction is very characteristic, the results were controlled by histological studies or by subsequent immunity tests.
Evidence of multiplication of the virus was obtained by demonstration of the minute paired micro-organism of the disease (Dermacentroxenusrickettsi) in increasing numbers in first generation cultures up to about the fourteenth day. The micro-organisms are always intracellular, in large amœboid phagocytic cells of endothelial origin.
The accompanying table shows the duration of survival of the micro-organisms in first “generation” cultures, experiments of August 17, October 10 and October 24, and the prolongation of this period by transplanting the cultures into fresh plasma; experiments of October 31 and November 7.
The examination of cultures fixed in Zenker's fluid, sectioned and stained with Giemsa's stain, shows that the period of survival of the micro-organisms corresponds to the length of survival of the cells of the culture. Initial multiplication of the micro-organisrnls takes place in situ in endothelial cells of blood vessels, and continues in wandering cells of the same origin.
The examination of cultures fixed in Zenker's fluid, sectioned and stained with Giemsa's stain, shows that the period of survival of the micro-organisms corresponds to the length of survival of the cells of the culture.
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