EATS AND PLAGUE. 31 



since the great fire of February, 1904, has been reasonably free from 

 rats until the past year. However, many of the large modern build- 

 ings erected in the burnt district are now infested with rats. Losses 

 from rats in the markets of Baltimore are less than in those of Wash- 

 ington, not because rats are scarcer, but because Baltimore enforces 

 more stringent regulations as to the storing of goods and the arrange- 

 ment of fixtures in the stalls. Based on its population and commer- 

 cial importance as compared with Washington, the total losses exceed 

 $700,000 a year. If similar conditions hold for all cities of over 

 100,000 inhabitants in the United States, as they probably do, depre- 

 dations of rats and mice in these centers of population entail a direct 

 loss to the residents amounting to the enormous sum of $20,000,000 

 annually. 



RATS AND PUBLIC HEALTH. 



The most serious charge against rats grows out of their relation to 

 human health. It is now positively known that rats are chiefly 

 responsible for the spread of bubonic plague, a malady which, in spite 

 of modern methods of fighting it, has within the past dozen years 

 destroyed over 5,000,000 human beings in India alone. During 1907 

 the deaths from plague in India were 1,200,000, and by May, 1908, 

 the present epidemic, which started in China in 1894, had invaded all 

 the continents and infected 51 countries of the world. The identity 

 of plague in man with plague in the rat was proved some years ago, 

 but the particular means by which the disease is transmitted from 

 rat to rat and from rat to man was not clearly understood until 

 recently. The fact that fleas carry the infection was set forth posi- 

 tively as early as 1902, but the conclusions of the India Plague Com- 

 mission have finally removed all doubt upon the subject. The results 

 of two years of exhaustive research were recently published in a 

 pamphlet which thus summarizes the conclusions concerning bubonic 

 plague : 



1. Bubonic plague in man is entirely dependent on the disease in the rat. 



2. The infection is conveyed from rat to rat and from rat to man solely by means of 

 the rat flea. 



3. A case of bubonic plague in man is not in itself infectious. 



4. A large majority of plague cases occur singly in houses. When more than one 

 case occurs in a house the attacks are generally simultaneous. [This proves that there 

 is no soil infection.] 



5. Plague is usually conveyed from place to place by imported rat fleas which are 

 carried by people on their persons or in their baggage. The human agent not infre- 

 quently himself escapes infection. 



6. Insanitary conditions have no relation to the occurrence of plague, except in so 

 far as they favor infestation by rats. 



7. The nonepidemic season is bridged over by acute plague in the rat, accompanied 

 by a few cases amongst human beings. 



a Etiology and Epidemiology of Plague, p. 93. Calcutta, 1908. 



