THE RAT AND ITS RELATION TO THE PUBLIC HEALTH. 



By WALTER WYMAN, 

 Surgeon-General of the Public. Health and Marine- Hospital Service. 



INTRODUCTION. 



The science of bacteriology has elucidated many facts with respect 

 to the causation of disease, and with this advance in knowledge, old 

 theories regarding the miasmatic and humoral origin of human ills 

 have been abandoned. 



Epidemiological studies have likewise determined the methods of 

 transmission of many of the infectious and contagious diseases, thus 

 eliminating erroneous conceptions that they are attributable to 

 some mysterious condition of the atmosphere or soil, or to a visitation 

 of the wrath of the Almighty. 



Both these sciences have contributed to our knowledge of the 

 relationship of living things, particularly with respect to their influ- 

 ence upon each other in relation to health and disease. It is now 

 known, for instance, that mosquitoes are the pests of man, not only 

 because of their bites, but because they at times transmit malaria, 

 dengue, nlariasis, and yellow fever. So, too, it is known that rodents 

 are the enemies of man, not only because of the toll exacted from 

 him, but because they are the principal agents in the propagation 

 and spread of bubonic plague. 



Ancient writings abound in allusions to pestilences and their con- 

 nection with epizootics among rats and mice. 



In the Book of Samuel there is reference to a pestilence having 

 relation to mice, and that it might be stayed the Philistines made 

 ^offerings of golden images of the mice that marred the land. 



During the centuries that have intervened rats have migrated to 

 practically every quarter of the earth, causing untold losses on 

 account of their depredations. They have also, in all probability, 

 been the primary agents of transmission in the pandemics of plague 

 which have visited the earth. The fact that plague is due to a 

 specific microorganism, and that its presence in man is also asso- 

 ciated with epizootics in rats, has led to a more careful study of this 

 animal, particularly in relation to his habits, the diseases from which 

 he suffers, and the methods necessary to his control. Prior to the 



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