Sessional_Paper_1904 — Page 727

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In District No. 10, the condition is almost identical. A rather unexplain- able fall in the epidemic curve occurs. This may be due to sanitary interference or to the fact that such cases as were present, cleared out of Hongkong as soon as the district became suspiciously plague infectel. Such variations in the curves must occur and are impossible to clear up, when one has to fight for knowledge amongst natives, who frequently turn their densest ear towards one, whenever information regarding cases of suspicious sickness is requested.

Other variations in the epidemic curve are forthcoming in Districts Nos. 6 and 8. Here the elevation to the maximum of the epidemic is certainly post- poned for a considerable time.

It is difficult to account for suc, but on going into the question with such detail as I have done, in the presence of a native population, and rigorous sanitary measures, it is surprising to find so many of the charts which give accurate in- formation in regard to the incidence of the epizootic and the epidemic. In the remaining districts the maximum elevation of the epidemic curve was low, not- withstanding an occasional appreciable elevation in the curve of the epizoo'ic. A close examination of the relation of the epidemic curve to that of the epizootic will enable one to conclude that the course of the epizootic curve is in the majority of instances responsible for the shape of the epidemic curve.

The Fastigium. In the general curve for 1902, a good idea is obtained o. what holds good of or each individual district, in regard to the maintenance of the elevation of the epizootic and the epidemic. The sudden rise of the epizootic to its maximum is not usually long maintained. A fall for some considerable distance takes place, with a subsequent maintanance of a lowered elevation for some weeks. The epidemic in general shows the same character.

The general curves for each individual district show practically the same as that which obtains in the general curve. The elevations and depressions at and about the maximal extent of each curve follow each other closely. The same close relation between human and rat plague is shown during this stage of the outbreaks.

The Defervescent of the Curves.--In order to bring the epidemic curve into close relation with that of the epizootic, this part of the outbreak is of the highest importance.

We have seen so far that ascent, and maximal elevation with variations, the two curves follow each other closely.

From this alone one could not claim to have established a connection between the two outbreaks, all one could say is that both occur about the same time. but probably occur quite independently of each other, at least the question would be asked, given these two curves, the one as it w re lying within the other, what points in these lead on to the conclusion that the one is the result of the other.

The history of the outbreaks is useful. We have 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 point 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 plaque. These questions and 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 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 epizootic, human plague should more or less

cease.

The preliminary part of these curves have been followed. They are seen more or less to 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.