12 QUATERCENTENARY STUDIES IN PATHOLOGY 



but probably quite independently of each other. At least, the question 

 would be asked, that, given these two curves, the one, as it were, lying 

 within the other, what points in these lead to the conclusion that the 

 one is the result of the other ? 



The history of the outbreaks is useful. It is seen that the epizootic 

 precedes the epidemic by about a fortnight ; that variations in the 

 epizootic are followed by variations in the epidemic ; that their maximal 

 points more or less correspond ; and, in general, a superficial glance at 

 the curves makes one think of the extremely close relation which must 

 exist between the two outbreaks. But it must be remembered, that rat 

 plague may be present without the advent of human plague, and vice 

 versa, and that occasionally the amount of rat plague bears no relation 

 to the amount of human plague. These questions, and even others, 

 must be answered before accepting the statement that in rats we have 

 the key to the problem of plague prevention. 



The general curve for the year 1902 shows the epidemic curve almost 

 surrounded by that of the epizootic. From this chart alone it could not 

 be concluded that the one is the cause of the other ; if so, we should 

 expect the rat plague curve to fall inside that of the epidemic curve. 

 Shortly, if there is a connection between the epizootic and the epidemic, 

 the latter should rise according to the elevations in the epizootic, and, 

 with a fall in the latter, human plague should more or less cease. 



The preliminary parts of these curves have been followed. They are 

 seen to more or less harmonise. The point now to be considered is the 

 relation existing between the epidemic and the epizootic towards the 

 close of the outbreaks. If the latter is the cause of the former, it should 

 fall previous to the decline in epidemic plague. In the general chart for 

 the year 1902, the rat plague curve has just missed falling inside that of 

 the epidemic. Here, however, we are dealing with an extremely mixed 

 collection of results, taken from the City of Victoria as a whole. In 

 Hong-Kong the city is divided up into a series of Health Districts. By 

 comparing the relationships between the two outbreaks in individual 

 districts, results of even a more convincing nature are obtained. By 

 viewing the results according to this plan, a sufficient complement of 

 epizootic and epidemic plague is obtained, and more accurate conclusions 

 drawn. The dearth in the number of cases of the epidemic, and the 

 excess in that of the epizootic vitiate what would otherwise have been a 

 positive result. (226) 



