In preceding studies two of us1reported, among other things, that theRickettsiaof Mexican typhus fever will remain alive and virulent within the bodies of bedbugs and of three varieties of ticks for periods as long as from ten to fourteen days. Dyer, Rumreich and Badger2have recently recovered the virus of the North American type of the disease from fleas collected from rats caught in a typhus focus. These investigations, showing thatRickettsiacan survive in and perhaps be transmitted by a number of blood-sucking insects parasitic on both animals and man, give strong experimental support to the suggestion made by Maxcy3in 1926 to the effect that there might be a reservoir of typhus infection in some species of domestic animal from which the disease can be conveyed to man by an insect vector, possibly "fleas, mites or ticks." In studying the epidemiology of