10 



beginning of the present pandemic of plague which had its origin in 

 China, interest in the rat was almost wholly an economic and finan- 

 cial one. Since that time evidence has been rapidly accumulating 

 which proves that this animal and his parasites are responsible for 

 the transmission of plague and that plague itself is essentially a 

 disease of the rat. 



A knowledge of this animal on the part of the sanitarian therefore 

 becomes essential. During the enforcement of antiplague measures 

 in California, Hawaii, the Philippine Islands and elsewhere, observa- 

 tions of great value have been made and their practical application 

 has resulted in better directed efforts for the elimination of the 

 disease. 



In studies of plague and leprosy with the view to their diagnosis 

 and control, it is not enough now' to isolate the microorganisms 

 responsible for these diseases, but the sanitarian must be able to 

 recognize the pathological conditions present in animals affected, 

 and to do so he must have practical knowledge of this subject in 

 order that he may differentiate between the various diseases from 

 which these animals suffer. 



Opportunity for observation and study of the diseases of rats and 

 the methods necessary to their eradication has been afforded to the 

 officers of the Public Health and Marine-Hospital Service who are 

 constantly stationed on the outposts in the warfare against exotic 

 diseases. The results of these observations have been utilized by 

 officers of the service, and some of them have been published for 

 the benefit of others. 



The rat has received much attention of late in other parts of the 

 world. In Denmark, for instance, a legalized warfare against rodents 

 has been'begun, principally on account of their influence in the trans- 

 mission of trichinosis. In England there exists The Incorporated 

 Society for the Destruction of Vermin, and in other places rat 

 destruction is being agitated both from economic and public health 

 standpoints. 



In view of the great importance of the rat in relation to the public 

 health, it has been thought advisable to coUect and publish all 

 pertinent information on the subject, in order that public health offi- 

 cials who should be on the lookout for the appearance of plague 

 among rodents might have available a reliable treatise on the subject. 



Studies of rodents from a biologic and economic standpoint come 

 within the province of other departments of the public service, and 

 the cooperation of the Biological Survey and Bureau of Entomology 

 of the Department of Agriculture was therefore requested and 

 received. 



The subjects dealt with in this publication have been prepared 

 by those having wide experience. 



