Normal adult Wistar rats (non-carrier stock) are readily infected with Bartonella muris and develop a severe anemia if large amounts of infecting material are used. The normal adult rat of Wistar stock possesses a relatively high natural resistance to spontaneous infection with this organism.

Bilateral suprarenalectomy in Wistar rats lowers the natural resistance to a subsequent infection with Bartonella muris. This procedure does not alter the type of tissue response to the virus but lowers the natural resistance of the rat to toxic effects of the infection. The acquired immunity to Bartonella muris conferred by a first infection is not broken down by subsequent suprarenalectomy.

The mechanisms of acquired and natural resistance are dependent on different physiological processes in the organism and are not merely quantitative variations of the same process as is generally assumed.

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