Sessional_Paper_1904 — Page 728

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There are other considerations which must be brought forward, which do show the close inter-relationship between rat and human plague. It will be of interest, however, to examine as to how far this question may be answered affirm- atively. In the general chart, 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. The condition of affairs in each individual district is of much greater interest,

In order to show the relationship between the fall of the two curves, it is necessary to have a sufficient complement of epizootic and epidemic. As we bave seen, the epizootic is usually in excess. The number of cases of the epidemic may be so small as to vitiate what would otherwise have been a positive result.

Therefore in drawing conclusions as to this point only charts showing a goodly number of both outbreaks in fairly equal proportion can be used.

The Kowloon chart like the general chart (which also includes Kowloon) shows a very large preponderance of the epizootic. A close examination of the two curves, however, will convince one that had the epidemic been in anything like proportionate numbers, its defervescence would have followed and not imme- diately preceded that of the epizootic.

The experience gained in other districts is of the greatest interest in this respect.

In all the districts in Hongkong in 1902, with three exceptions, the charts show that the epizootic falls first and is followed by the epidemic. Immedi- ately the rut plogue diminishes or diappears human plaque becomes more or less extinct. In order to convince oneself of this, a glance at the charts of Health Districts Nos, 2, 5, 9, and 10 is sufficient. A similar condition of affairs is also to be found in the charts of the Districts Nos. 1, 3, and 6.

The three exceptions mentioned, namely, those found in Districts Nos. 4, 7 and 8, come under the same category as the general chart and that for Kowloon. rat plague is severe, but the epidemic is slight. This being so, an opportunity is not afforded to compare the one curve with the other.

The Subsequent History of the Curves.

Again this is of the greatest interest. Many points are worthy of close study in regard to the continuance or decline of one or other of the outbreaks. The general chart shows us that the epidemic becomes extinct. A few cases occur erratically, but no further epidemic takes place.

The epizootic falls and to all appearance looks as if it were to disappear also. This is not so, however; it never becomes extinct, It remains in abeyance for a week or two, subsequently breaking out in considerable numbers.

This recrudescence of the epizootic is not followed by the «pidemic.

The type of curve of the recrudescent epizootic is totally different from that of the main outbreak. The rises and falls of the curve are gradual not precipitous like the onset and course of the primary curve. This recurrant epizootic is seen to maintain itself in considerable force until the end of the year.

Such a discovery is of great significance in regard to the possible recurrence of the epidemic in the different districts. This part of the epizootic and its signi- ficance is considered under a separate heading.

Noteworthy is the severity of the epizootic during the last quarter of 1902 in the following districts: Kowloon Nos. 2, 6, and 8. It will be interesting to follow the course of events in these districts during the early part of 1903, and trace as far as possible the influence of a mild or a severe epizootic towards the end of the year, on the outbreak of the epidemic in these particular districts.

The foregoing represents as shortly as possible a resumé of the results of my investigations into the rat question during 1902.

In my opinion, the results are better than were at first expected. Notwith- standing many initial defects in the whole system of rat examination, the research has brought out many points bearing upon the course of the epizootic and its pos- sible relation to the epidemic.