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It is a point of considerable interest to find the existence of marked rat plague without the presence of cases in man. The details furnished by the charts of each district are of importance in this respect. It is seen that in some districts the advent of human plague is delayed for some considerable time. The epide nic had by this time made its appearance in Hongkong, but some districts remained free. In these latter districts the curves are interesting The human plague curve is at zero, and what is of importance, the epizootic may be high but maintains this height with constancy. After a month or two a sudden rise-small. or great-in the rat plague curve takes place. What happens now, is the regular appearance of human plague.
On following out these details in each district, one will see that the rat plague becomes epizootic, so to speak, at different times in different districts, and what is so conclusive, in regard to the relation of the one outbreak to the other, is the incidence of human plague at corresponding times in each district. Human plague appears regularly after the occurrence of the epizootic. The interval between the two outbreaks rarely exceed a fortnight. We have therefore in one large city like Hongkong, au epidemic of plague. The city divided into a number of Health Districts. The epidemic is not equally spread over the city. Certain Health Districts are severely affected; in others, the epidemic is non-existent.
Why is this so? Districts may alj in each other
human plague; the other may be practically free.
One may be furnishing
A glance at those charts which have been prepared will help us to settle the question in our minds.
In all districts furnishing hutoan plague, the epizootic is present in great excess, and the epidemic would appear to be proportionate to the epizootic.
In all districts furnishing rat plague-but not an ever-increasing epizootic- human plague is usually absent. One or two cases may occur, but no epidemic breaks out. In any plague rat infected district, an increase in the epizootic means the appearance of human plague. In regard to the 1903 epizootic and epidemic, these conclusions appear to be warranted. The epidemic was a large one, at least for Hongkong; every district was more or less epizootically and epidemic- ally infected.
Similar to the outbreak of 1902, Kowloon was grossly epizootically infected. The epilemic was also more prevalent in this part of the Colony than in any other Health District. With regard to the epizootic, not a single week passed without the occurrence of several cases of rat plague in Kowloon.
A minute examination of the course and relations of the curves would be superfluous They speak for themselves, and when considered by the examiner in the same way as I have treated those of the 1902 outbreak, become perfectly intelligible.
WILLIAM HUNTER.
The History of Hongkong during 1903.
A very important point in connection with the determination of the relation of the epidemic to the epizootic, is that one is now enabled to follow closely the train of events from the commencement of the year. On the 1st January, 1903, rat plague was existent and constituted more or less of a definite epizootic. On the other hand there was no trace of an epidemic. If reference he made to the curves of the epizootic and epidemie 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. The epidemic was nil. Such a condition of affairs did not hold good for the commencement of the new year 1903. Almost immediately the epidemic appeared, and subsequently both this and the epizootic ran very characteristic charts.
The com-
Within a fortnight of the new year, human plaque was present. mencement of the 3rd week of January marked the advent of the 1903 epidemic of pest.
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