With a view to determining the mode of infection in Carrion's disease, a study of the blood-sucking insects found in the districts of Peru where the disease prevails has been carried out, through the cooperation of The Rockefeller Institute and the Rockefeller Foundation. The material studied included ticks, mites, midges, lice, fleas, bedbugs, mosquitoes, buffalo gnats, horse-flies, "sheep ticks," 3 species of Streblidae, and 3 species of Phlebotomus, including Phlebotomus verrucarum Townsend and two new species which have been named Phlebotomus noguchii and Phlebotomus peruensis. The insects were collected without the use of chemicals, were prepared for transportation in such a manner as to prevent drying, and were shipped under conditions of refrigeration to New York, where they were inoculated into monkeys. The plan followed was to inject saline suspensions of the crushed insects intradermally into rhesus monkeys and to make cultures of the blood of the animals at intervals of 1 to 6 weeks after inoculation.

The only class of insects in which the presence of Bartonella bacilliformis could be detected were phlebotomi. No cutaneous lesions were induced in monkeys injected with the crushed insects, but in the case of four different lots of phlebotomi the blood of the animals so injected yielded cultures of Bartonella bacilliformis which produced typical verrucous lesions on inoculation into other monkeys.

The morphology and cultural characteristics of the Bartonella strains obtained from phlebotomi proved identical with those of strains isolated from human blood and skin lesions. Monkeys which had recovered from infection with the phlebotomus strains resisted inoculation with a human strain of Bartonella bacilliformis, and, conversely, monkeys which had passed through an infection induced by the human strain resisted inoculation with the strains obtained from phlebotomi.

The experimental observations described in this paper lead us to conclude that certain phlebotomi act as insect vectors of Oroya fever and verruga peruana. The phlebotomi which have been shown quite certainly to carry the Bartonella bacilliformis are those of the species Phlebotomus noguchii. Phlebotomus verrucarum is also probably a vector, while Phlebotomus peruensis remains doubtful in this respect.

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