So long as members of a community are content to live in association with rats and fleas correlative plague is a likely result. Meanwhile, plague prophylaxis consists mainly of warfare against rats, in the hope of ultimately banishing them from human habita tions and from contact with man. Any general elimination of these pests over wide areas is a slow, costly and usually impracticable affair, and all that can be achieved in most cases is some degree of palliation by rat-proofing of grain stores, wharves and other places which serve as centres for the dissemination of plague. Destruction of rats by trapping and poisoning is a commendable procedure, but of itself will never eradicate endemic plague, for the losses in the rat population are quickly made good if sur vivors are provided with food and harbourage. An important measure of personal prophylaxis is inoculation with anti-plague vaccine, which affords a good degree of protection. Persons enter ing plague-infected houses should wear gaiters, and otherwise render their clothing as flea-proof as possible; if there is any suspicion of pneumonic plague, goggles, and masks made of sev eral layers of fine gauze, should be worn without fail.