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338 in a proportion of instances the plague germ is introduced through trifling wounds of the feet. It is conceivable that such germs as may be lying about on the ground, deposited there in the discharges of sick human beings or of plague-stricken animals, or perhaps growing there in natural culture, may be picked up in this way. The frequency with which the primary bubo, as will be pointed out, is located in the deep femoral glands favours this idea. One can understand, too, how lice, fleas, bugs, and perhaps flies might act as carriers of the virus from person to person, inserting it with their bites, or inducing scratching and superficial skin lesions, through which the virus obtains entrance.* Yersin found that the flies in his Hong Kong plague laboratory died in great numbers, their bodies being crowded with the specific bacillus; he injected bouillon containing a trituration of one of these flies into a guineapig, and the animal presently died with all the signs of plague. Sablonowski, who in 1884 in a measure anticipated the discovery of the bacillus by Kitasato and Yersin, remarked that during the Mesopotamian epidemic of that year a certain species of fly appeared and disappeared concurrently with the plague he considered that this insect was an active agent in spreading the disease. That the plague bacillus does at times enter the body through the unbroken skin or mucous membrane is made highly probable (1) by the absence in the great majority of cases of human plague of evidence of an initial skin lesion; (2) by the success of experimental feeding of animals with plague tissues or cultures; (3) by the ease with which infection is conveyed through the air to man and other animals in pneumonic plague; and (4) by the certainty with which rats can be infected by simply smearing a plague culture on the shaven skin.

Age, sex, and occupation have very little influence in plague. The youngest children are susceptible;