Tke Rat Theory of Flague Epidemics. 



In all the plague treatises which have been published during the 

 past year or two, one finds a considerable amount of attention devoted 

 to the question of the occurrence of plague infection in rats, and 

 the dangers attached to the presence of such infected vermin in the 

 direct vicinity of man. The dictum of Koch and many epidemiologists, 

 that plague is primarily a disease of the rat, secondarily a disease of 

 man, and that epidemic plague is entirely dependent on the presence of 

 widespread plague infection in rats, has become widely recognised and 

 accepted by many plague experts. If we look into the evidence in 

 favour of such a conclusion, however, little information of a definite 

 nature can be obtained. Up to the present time, no research has been 

 accomplished which would justify the conclusion that plague-infected 

 rats are the chief sources from which the virus is communicated to man. 

 It must be admitted that there is much evidence in favour of such a 

 method of transference, but, notwithstanding the constant influx of 

 additional evidence, there yet remains to be shown the direct connection 

 between epizootic and epidemic plague. 



It is only within the past few years that the occurrence of disease in 

 animals has become fully recognised as an important disturbing factor 

 in the successful dispensation of modern sanitation. With the advent of 

 more perfect knowledge in regard to the ways of infection, attention has 

 become directed to the occurrence of diseases in animals, diseases which, 

 when compared with those found in man, appear to be similar. The 

 question has, therefore, arisen — a new one indeed — as to the part played by 

 animals in the dissemination of certain diseases amongst the human race. 



At the present day, one cannot take up a book dealing with plague, 

 without being struck with the prominent part devoted to rats as 

 disseminators of infection. In fact, on the perusal of many such manu- 

 scripts, one is drawn to the conclusion that rats, and nothing but rats, are 



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