PRESIDENTIAL ADDRESS. 5 



carrier par excellence. Further, the plague is a disease of 

 the rat which is afterwards transferred to man. In other 

 words the epizootic precedes the epidemic. This disease in 

 rats has been observed from great antiquity, but only after 

 the discovery of the Bacillus pestis was it recognised to 

 be really plague. This being established the intimate 

 life-histories of the rat and of the different kinds of flea 

 become of supreme importance, for probably these if better 

 known would clear up many of the mysterious points in 

 connection with plague. For instance, every year in 

 Sydney the flea nuisance troubles us in the beginning of the 

 year, but this is just the time at which the plague is with 

 us. Is it also the time when the rat is most numerous ? 

 An interesting point in the Commissioners' Report is 

 the use of the guinea pig as a flea-trap. The guinea 

 pig normally does not harbour fleas, but they take 

 readily to the guinea pig when they get the chance, 

 and so the guinea pig put into plague rooms is soon 

 attacked by the fleas, which can then be readily picked 

 from the guinea pig or shaken or combed out after chloro- 

 forming the guinea pig and the fleas at the same time. 

 The fleas thus collected in such rooms were largely rat fleas, 

 and so also were those collected upon the bodies of plague 

 patients. Fleas collected from plague rats had their 

 stomachs full of Bacilli pestis, and placed upon healthy 

 guinea pigs or healthy flealess rats communicated the 

 disease. Healthy rats in plague rooms, but surrounded 

 by fine protecting wire gauze, remained healthy. Ob- 

 viously fleas could not get through the gauze. Surrounded 

 by an area 6 inches wide of " tangle-foot," the animal 

 did not become plague stricken in plague rooms as they 

 did if unprotected. Obviously the flea does not jump so 

 far as one usually gives it credit for. The fleas stuck in 

 the " tangle-foot " and could be easily picked off. Of 247 

 caught 60°/° were human, 34°/° were rat fleas, and Qf cat fleas. 



