14 QUATERCENTENARY STUDIES IN PATHOLOGY 



On the 1st January, 1903, rat plague was existent, and constituted 

 more or less a definite epizootic. On the other hand, there was no 

 trace of an epidemic. If reference be made to the curves of the epizootic 

 and epidemic during the last quarter of 1902, it will be seen that the 

 former raged more or less incessantly ; whereas the epidemic, apart from 

 one or two sporadic cases of plague, was non-existent. The epizootic 

 maintained an average level of from 20 to 30 cases per week. Such a 

 condition of affairs did not hold good for the commencement of the new 

 year 1903. Almost immediately the epidemic appeared, and subse- 

 quently both this and the epizootic ran very characteristic charts. 

 Within a fortnight of the new year, human plague was present (Chart 

 IV.). The commencement of the third week of January marked the 

 advent of the 1903 epidemic of pest. A careful survey of both curves, 

 will enable one to draw one's own conclusions. Although the rat plague 

 is in excess numerically, the rises and falls of the epizootic curve are 

 followed only too closely by similar elevations and depressions in the 

 incidence of human plague. One rarely observes such a following of one 

 curve after another. The apices of both curves are found to correspond 

 with the result obtained during the year 1902. Both reach their highest 

 points within a fortnight of each other, the epizootic being first. 



The course of events, after the outbreaks have reached their highest 

 figures, is interesting. The epidemic falls in numbers so rapidly, that, 

 practically within a month, the number of cases of human plague has 

 fallen to an insignificant figure. But what is even more remarkable, is 

 the sudden drop in the epizootic. The time occupied by the epizootic in 

 falling from its maximum to its lowest level is about 15 weeks. The 

 epidemic took about 13 weeks, namely, about a fortnight less. 



The subsequent history of the curves is not so interesting. Rat 

 plague never disappears. Human plague is practically absent. This 

 interval between the incidence of human and rat plague appears to be 

 more or less constant. In the year 1902, the interval between the 

 occurrence of both outbreaks was from 10 to 14 days. The course of 

 events during 1903 leads us to the same conclusion in regard to the time 

 limit. 



Comparing, therefore, the curves for both years we find that the 

 epidemic begins a fortnight later than the epizootic ; it reaches its 

 maximum a fortnight later ; this maximum is maintained for a similar 



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