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Scientific Memoirs by

increase to any marked extent until July. This is due to the fact that, at the
beginning of the rains, in this place, the ground-water is always from 35 to 40
feet from the surface of the ground, and, in the year 1895, was still 28 feet down
at the end of June in spite of almost to inches of rain having fallen during that
month. As soon, however, as there has been heavy rain in July on the top of that
of June, the fever begins to rise and continues to be prevalent as long as, or rather
longer than, the rain lasts, declining again in October, or even in September
in such years as the rains terminate early, as in 1891 and 1887, but going
on into November or December in years in which the rains continue later
than usual as in 1889 and 1893, in the latter of which there was very heavy
rain in September.

       A further study shows that there are two main factors on which the
amount of fever in any given year depends. These are, firstly, the amount
of the rain, and, secondly, the regularity or irregularity of its distribution.
On these depend the height to which the ground water will rise and the
rapidity and amplitude of its variations of level; and, if my supposition that
the amount of fever in any given year in this place will depend on the amount
of displacement of the ground air, carrying up the organisms into the atmos-
phere, is correct, then the amount of fever should depend on the amount and
irregularity of the distribution of the rainfall. Let us see whether this is the
case or not.

       If the years 1887 and 1892 be compared, it will be seen that the charts
of the rainfall show much the same character, inasmuch as there was no
very excessive fall in any month, but the fever rate was very high in the
former year, while there was practically no fever at all during the rains in the
latter. If, however, the quantity of rain be noted, it will be seen that in 1887
the rainfall was considerably in excess, amounting to over 70 inches, while in
1892 it was less than normal, being only 52.53 inches. The water must, then,
have risen much higher in the former year, It will also be noticed that
the rains began very early in 1887, namely in May, so that the ground-water
must have been very high during July and August, while, on the other hand,
the rains stopped early, and so the fever rapidly fell in September and October.

       Again, if we compare 1892 with 1894, it will be seen that in the latter
year, not only was the rainfall in excess, but it was also unevenly distributed,
so that there was over 19 inches in both July and August. Here, then, we
have both factors well marked, and it is worthy of note that, in this year, the
fever is higher than any other year of the series, and that there was 12 times
as much fever this year as there was in 1892; and, if only that in the rainy
seasons be counted, which, for reasons which will appear later, gives the most
correct comparison, then it was 30 times as much. The practical absence of
fever in the rainy season of 1892 remains to be explained, as it is very extra-