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As some cases of Plague are discovered carly, some when the disease is well marked, and most others only when the patient is dying or dead, the slight varin- tions of the Plague curve from day to day cannot be taken as strictly showing how many cases should properly speaking be assigned to each day. The general trend of the curve with its marked rises and falls will serve however to give an idea of the behaviour of the epidemic relative to the meteorological data.
Although it would seem that the rise of the mean temperature to above 80° F. in some way affects the Plague curve, yet it must not be ignored that with a fall of temperature in the autumn months to heights corresponding with those in the spring months there is no recrudescence of the epidemic recorded. In August of this year the mean monthly temperature was 809 and the number of cases of Plague 31. From 80·1° F. on the 14th the mean fell to 75-9° F. on the 18th but from the 18th to 31st of August there were only 5 cases. In September the monthly mean of the temperature was 786 with its lowest point 76 on the 12th; the number of cases in this month was 9; 4 before, 1 on, and 4 after the 12th day. As the meteorological observations for October of this year are not yet published, I may use last year's return for this purpose. They shew that the October tempera- ture for the month was 767. November of last year had a mean temperature of 715. When in April and May of this year the mean temperature was 724 and 75.4 respectively Plague was very severe.
RAINFALL AND PLAGUE.
On the
Although the rainfall in December, 1902, was very small, yet it will be seen on reference to the chart shewing Sunshine, Rain, and Plague Curves, that there was some rain on 9 days out of the first 18 days of that month. 19th day a case of Plague was notified. From the 22nd to 30th days rain fell on 5 days. There was a case of Plague on each of the 27th, 29th and 31st days.
Coming to January of this year it will be seen that there was rain on 5 days from the 10th to the 14th inclusive, and a case of Plague on the 16th. During the spell of dry days, from the 15th to the 24th, 3 cases of Plague were discovered. From the 25th January to the 2nd February, however, there were 6 days in which rain fell; from February 2nd to 6th inclusive there were 12 cases of Plague. During the next 3 weeks which were dry there were 14 cases only. In the eight following days, i.e., up to March 7th, rain fell on 7 days. The Plague curve shows that at this date the epidemic was established. Altogether in March rain fell on 16 days and the Plague curve continuously but slowly rose. In April from the 3rd to the 10th inclusive, no rain fell; the eight days from the 5th to the 12th shews a considerable fall in the number of plague cases. The fortnight from the 17th to the 30th had 8 wet days and the Plague curve is shewn to be considerably higher.
The month of May shews similar facts, there being 17 wet days with gener- ally much heavier daily falls than before. Through May to June 8th the Plague curve rises to its highest point but the very heavy fall of rain in the latter half of this month is not followed by a rise in the Plague curve. It will, however, be noted that the heavy fall of rain in the last week of June amounted to a small flood and although the interiors of houses would not be benefited directly by this, yet it might have otherwise some beneficial effect.
The 26th week of this year was that between June 24th and 30th inclusive. This week has the heaviest rainfall curve of the year; a reference to the chart given under rat Plague will shew that there was a sudden heavy fall in the 27th week in the percentage of Plague infected rats, namely, from 8 to 3.2, The thorough scouring out of the sewers and storm water drains especially which such rain would effect inay well have something to do with this. It will be seen that at the week ending June 15th 2,382 rats were caught but that by July 13th this was reduced to 1,674- a drop of over 600 per week. If us has been mentioned before large numbers of rats were being imported for the sake of the bonus the fall in the percentage of infected rats amongst those daily collected might be accounted for.
SUNSHINE AND HUMIDITY.
Ihe relative risings and fallings of the curves of Plague and Sunshine are to a great extent inverse to those of Rain and Plague. The 3rd week of March is a good example. The relatively large amount of sunshine from the 4th to the 10th of April accompanies a fall in the Plague curve, but as I shewed under Tem-