389
It is probable, however, that the unknown cases amongst human beings bear a far less proportion to the total human cases than do the unknown rat cases to the total rats infected.
The Tables accompanying the curves shew the numbers of rats caught in each district and the actual numbers of rats reported as infected for the same periods covered by the curves described above. In addition they shew the populations (estimated to January 20th, 1904, i.e.. the middle of the 12 anonths under conside- ration) of the different districts, with the actual numbers of plague cases for the same periods.
Taking the City of Victoria as a whole the Table and curves shew the tail end of the 1903 and the rise and greater part of 1904 epidemics and epizootics, with, in the case of human plague, the period of eight weeks, from the 50th week 1903 to the 5th week 1904 during which no cases are known to have occurred,
The rat curve may be divided into five periods or waves during which the plague incidence rose and fell. The human curve may similarly be divided into three such periods or waves.
The first rat wave from week 31 to week 37, 1903-a period of declination— is accompanied by the declination of the 1903 epidemic.
The second rat wave from week 38 to week 48, 1903, is followed by a slight wave of plague in the 45th to 49th weeks, 1903.
The third rat wave, a slight one in weeks 49 to 51, 1903, is followed by eight weeks during which no human plague is known to have occurred.
The fourth rat wave from the 52nd week, 1903, to the 9th week, 1904; the fifth rat wave may be considered to begin in the 10th week, 1904, and continues to the 31st week.
The third human wave, however, begins at the 6th week, 1904, and rises and falls over the two last rat waves.
There, therefore, appears to be no constant relation between the rise and fall of rat plague and that of human beings.
The second rat wave reaches its highest point in week 42 but the second human wave does not appear till the rat wave has greatly declined there being a period of two weeks after the rat wave maximum and the appearance of plague.
The fourth rat wave rises to its highest point in 8 weeks while human plague does not appear until 6 weeks of this period have elapsed.