820 PATHOGENIC MICROORGANISMS 



monia and spread through four transmission generations in man in 

 the autumn of 1919. 



Plague Prevention. From what has been said in regard to the 

 transmission of the disease it is apparent that the prevention of plague 

 becomes very largely a question of rat extermination and protection 

 against fleas. Vigilance in observation of the mortality among rats in 

 endemic centers, for the discovery of early rodent foci is important. 

 International precautions depend upon quarantine against rats which 

 may easily be carried, and have been carried from country to 

 country, by ships and by rail. The disinfestation of ships by S0 2 

 by means of the Clayton apparatus, and by hydrocyanic acid gas 

 as described by Creel and Faget of the United States Public Health 

 Service, are among the important methods in use for the disinfesta- 

 tion of ships, sleeping cars, etc. Quarantine regulations and the 

 supervision of incoming ships is important. In the United States 

 a quarantine of seven days is imposed on ships arriving from plague 

 ports, a period which is probably not long enough. Precautions 

 must be taken to prevent the travel of rats along hawsers when 

 ships are docked at a wharf, and this is usually accomplished by 

 the application of large circular shields along the course of the 

 hawsers in such a way that rats cannot cross. 



When foci of plague are discovered in any community, wholesale 

 rat destruction and isolation of the focus, by destruction of build- 

 ings, ratp roofing of cellars, etc., must be resorted to. Blake has 

 introduced a system of which Castellani and Chalmers speak very 

 highly, the principle of which is that the rat extermination and 

 other precautionary measures are started in a wide circle about 

 the focus, working in toward the center, since work beginning at 

 the focus itself in an outward circle may easily serve to scatter 

 rats, rather than circumscribe them. In the Philippines and in 

 villages in which natives live in primitive huts, actual burning of 

 the houses has been resorted to, but this, too, may easily result 

 in merely scattering the rat population into the neighboring districts. 

 On a large scale, rat extermination is usually carried out by poisons 

 in which phosphorous paste is perhaps the most important method. 

 Of especial importance is the protection of food stores, and particular 

 attention to all depositories of food, grain, etc., about which rats 

 are apt to accumulate. 



BACTERIOLOGICAL DIAGNOSIS OF SUSPECTED PLAGUE CASES. Since 

 the bacteriological diagnosis of the earliest cases that occur is one of 



