future, more than they have been in the past, in devising schemes of quarantine and in attempts at stamping out the disease in already affected localities. The wholesale destruction of domestic vermin should go hand in hand with the isolation of plague-stricken patients.*[1]
The role of the flea in plague.— Yersin placed in the same cage healthy and plague-inoculated mice. The latter died first; but later the originally healthy uninoculated mice also succumbed proving that plague is communicable either through the atmosphere, by contact, or by ectozoa.
Yersin's experiment has been successfully repeated again and again, on mice, rats, guineapigs, and monkeys, and with many modifications. The result has been indisputable confirmation of Yersin's results, and further proof that bubonic plague is not communicable from animal to animal by simple confact or by atmospheric convection, but that it is readily communicated by ectozoa, especially rat-fleas —principally Xenopsylla cheopis †[2] (Fig. 67) which act as passive intermediaries and carriers of the bacillus. Zirolia and others have found that Bacillus pestis multiplies in the stomach of the flea, retaining its virulence for over twenty days and being passed
- ↑ * It is stated that the handling of a rat newly dead of plague is fraught with danger, whereas a rat that has been dead for some time and is cold and stiff may be touched with impunity; and it is surmised that the fleas of the newly dead rat are still in its fur, and quit it for the body of the manipulator, carrying on their probosces the bacilli of the disease, which they introduce when they proceed to feed on their new host. "When a rat has been dead for some time and the body is cold, the fleas have already forsaken it; hence the impunity with which the rat itself may be handled, but the danger of the locality in which it died and where the hungry infected fleas are awaiting an opportunity for a meal. The fact that the glands of the legs are usually the first to become implicated in the majority of cases of plague suggests that the virus is generally introduced through the skin of the feet or legs, which are just those parts most likely to be attacked by a flea picked up in walking across the floor of a room in which plague-stricken rats or other animals have died.
- ↑ † This is the rat-flea in the tropics. Ceratophyllus fasciatus, which attacks men as well as rats, is the rat-flea in temperate climates. Plague epizootics occur in mice, but are not associated with plague in man. Ctenopsylla wusculi does not readily feed on man.
