6 QUATEkCENTENAKY STUDIES IN PATHOLOGY 



The reports of English writers, during the past few years, admit the 

 importance of the rat in disseminating plague infection, yet the majority 

 of these investigations show that considerable difficulty is experienced 

 in perceiving how the infection can be conveyed from the rat to man. 

 Snow's observations note the incidence of plague in rats, but do not 

 suggest any connection between the epizootic and the epidemic. The 

 Indian Plague Commission does not lay any weight on plague-infected 

 rats as agents in the dissemination of plague epidemics. Bruce Low's 

 papers on Bubonic Plague, dated July, 1902, lead one to believe that 

 man and the rat are reciprocally infected. No evidence is forthcoming, 

 however, in regard to the question from a priori grounds. To explain 

 the transference of the disease from the rat to man, Hankin concluded 

 that plague in man stood in relation to the accessibility to rats, and that 

 probably some intermediary insect was necessary to communicate the 

 infection from rat to man. About the same time, Simond stated that 

 the epidemicity of plague was due to migrations of plague rats, and not 

 to human intercourse. Further, the experience of Ashburton Thompson 

 in Sydney, during the recent outbreaks of plague, is that plague rats 

 were the sole source from which the infection was communicated to man. 

 Still, as this writer has remarked, considerable systematic research is yet 

 required in order to establish definite proof that man and the rat, in the 

 usual circumstances of propinquity, are reciprocally infective. In Sydney, 

 every effort was made to settle the question. Much supplementary 

 evidence was obtained, and the conclusion drawn that infected rats play 

 an important,, if not the most important, role in the dissemination of the 

 disease. 



At present the general trend of opinion is against the causes which 

 have hitherto been advanced to explain epidemic plague. It miist be 

 difficult for a certain class of professional men to get away from the 

 time-worn causes of epidemic disease. Indeed, in all text-books on 

 plague, one still finds the old dogmas of infection most carefully 

 reproduced, namely, the solution of the problem by a recognition of: — 



{a) The communication of the infection from the sick direct. 



{U) Indirect means. 



{c) Place Infection, etc. 

 Such a table of causes would amply explain the epidemicity of plague, 

 but the adherents of such a classification of etiology would appear to 



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