The insect carriers, he believed to be one or more species of Simuliidæ, or black-flies. In support of this he stated that _Simulium_ appears to effect the same topographical conditions as pellagra, that in its imago stage it seems to present the same seasonal incidence, that it has a wide geographical distribution which seems to cover that of pellagra, and that species of the genus are known to cause severe epizootics. Concluding from his studies in Italy, that pellagra was limited almost wholly to agricultural laborers, he pointed out that the Simulium flies are found only in rural districts, and as a rule do not enter towns, villages, or houses. [Illustration: 146. A favorite breeding place of Simulium. Ithaca, N. Y.] When Sambon's detailed report was published in 1910, his theory was seized upon everywhere by workers who were anxious to test it and who, in most cases, were favorably disposed towards it because of the wonderful progress which had been made in the understanding of other insect-borne diseases. In this country, the entomological aspects of the subject have been dealt with especially by Forbes (1912), and by King and Jennings, under the direction of W. D. Hunter, of the Bureau of Entomology, and in coöperation with the Thompson-McFadden Pellagra Commission of the Department of Tropical Medicine of the New York Post-Graduate Medical School. An important series of experiments with monkeys has been undertaken by S. J. Hunter, of Kansas, but unfortunately we have as yet no satisfactory evidence that these animals are susceptible to the disease--a fact which renders the whole problem difficult. The accumulated evidence is increasingly opposed to Sambon's hypothesis of the transmission of pellagra by _Simulium_. This has been so clearly manifested in the work of the Thompson-McFadden Commission that we quote here from the report by Jennings (1914): "Our studies in 1912 convinced us that there was little evidence to support the incrimination of any species of _Simulium_ in South Carolina in the transmission of pellagra. Reviewing the group as a whole, we find that its species are essentially "wild" and lack those habits of intimate association with man which would be expected in the vector of such a disease as pellagra. Although these flies are excessively abundant in some parts of their range and are moderately so in Spartanburg County, man is merely an incidental host, and no disposition whatever to seek him out or to invade his domicile seems to be manifested. Critically considered, it is nearer the fact that usually man is attacked only when he invades their habitat." "As our knowledge of pellagra accumulates, it is more and more evident that its origin is in some way closely associated with the domicile. The possibility that an insect whose association with man and his immediate environment is, at the best, casual and desultory, can be active in the causation of the disease becomes increasingly remote."