Judging from the data which have been collected from the literature[12] on the transmission of plague (Table III), Simond seems to have been the first to call attention to the important part which blood-sucking insects, particularly fleas, play in the transmission of plague. Although many investigators have been successful in demonstrating the presence of _Bacillus pestis_ in the digestive system of blood-sucking insects, it was not until the experiments of Gauthier and Raybaud that the actual transmission of plague infection by fleas was convincingly proved. Ever since the exhaustive and conclusive experiments, which were carried out both under natural and artificial conditions by the British Plague Commission, and the work of Verbijtski, which antedates the British Commission, were presented, there has been no doubt that the transmission of plague by blood-sucking insects, particularly by the fleas, is one, although not the only, mode of spreading this disease. It is obvious, as Herzog correctly remarks, that the factors which are responsible for the spreading of plague must be considered individually in each epidemic and in various parts of the world as well. There is no doubt that the importance of any insect in the transmission of plague depends on its habits as well as on those of the host, be it either animal or man. [12] Centralbl. f. Backt., 1 Abt. (1897), =22=, 87, 437. Report of Indian Plague Commission (1898-99). Zeitschr. f. Hyg. u. Infectionskrankh. (1901), =36=, 89. Kolle und Wassermann: Handbuch der pathogenen Mikroorganismen (1903), =2=, 538. Zeitschr. f. Hyg. u. Infectionskrankh. (1905), =51=, 268. Journ. Hyg., Cambridge (1907-10), plague numbers. _Ibid._ (1908), =8=, 162, 260. During the recent outbreak of plague in Manila, several samples of bed-bugs from the beds of the plague patients and dog fleas from a plague-infected house were collected and examined, but with negative result. In spite of the fact that it adds nothing new to the question of whether or not plague can be transmitted by fleas, since the question has been conclusively answered by the work of the Indian Commission, nevertheless the following observations of a small outbreak of plague among animals, the spreading of which was due solely to fleas, are of interest. One wild rat was inoculated with strain Iloilo 3 of _Bacillus pestis_. The skin adjoining the root of the right ear was scarified, and a loopful of the culture was smeared on the scarified skin. The rat was found dead three days after the inoculation.