A pure culture of a microorganism resembling in morphology and pathogenic action Bartonella bacilliformis has been obtained from blood taken during life from a case of Oroya fever which ended fatally. The blood taken at Lima into citrate solution and transported to New York at refrigerator temperature yielded positive cultures 28 days after its withdrawal from the patient.

The strain of Bartonella bacilliformis thus isolated grows well on the semisolid leptospira medium, and also on slant agar containing animal blood. The initial growth is not readily recognizable to the naked eye, but the presence of the organisms can be determined by means of the dark-field microscope and by Giemsa and Gram staining methods. No growth has been obtained on the more ordinary culture media. The organism is an obligate aerobe, is Gram-negative, and under certain cultural conditions motile. All the forms which have been described as occurring in human red corpuscles may be found in the cultures, and in addition many granular and coarsely irregular forms have been met with.

The inoculation of cultures of Bartonella bacilliformis into Macacus rhesus produces infection and gives rise to effects which differ with the mode of inoculation. The intravenous injection of the culture into young macaques induces a prolonged irregularly remittent fever. The organism can be cultivated from the blood over a long period, and it has been detected within the red corpuscles of the monkeys, reproducing the precise appearances observed in human cases of Oroya fever.

The intradermal injection of the culture into the eyebrow of young macaques gives rise to nodular formations rich in new blood vessels and showing the bacilliform organism within the endothelial cells. From the experimentally induced nodules cultures of the organism are readily recovered.

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