On the influence of variations of the ground-water level on
the prevalence of Malarial Fevers.

BY

SURGEON-CAPTAIN LEONARD ROGERS, M.B., B.S., LOND., F. R. C. S., ENG., I.M.S.

   IN a paper read before the Calcutta Medical Society in January 1896,
I showed that the number of fresh cases of malarial fever in the men of the
11th Bengal Infantry rose and fell with the rise and fall of the ground-water level
of the lines in which they were living, to such a degree that the curve illus-
trating the four rises and falls of the ground-water, which occurred during
the course of the rains, was closely followed by the curve of the fever
prevalence. The two were practically parallel, and on two occasions a fall
of only seven inches, when the water was 16 and 8 feet respectively from
the surface of the ground, during three and four daily periods, was accom-
panied by falls of the fever to ½ and 1/3 respectively of its rate during the
preceding rises, facts which could only be explained on the supposition
that the infection was due to the inhalation of plasmodium malariœ which
had been carried up into the atmosphere by the displacement of ground air
by the rising water. The further fact that an examination of the blood of
76 consecutive cases of the fever, in each of which one specimen of blood
was examined with an oil emersion lens for an equal time, showed that the
organism was found in 50 per cent. of the cases which began during periods
when the ground-water was rising, but in just under 20 per cent. of those which
occurred when the water was falling, doubtless due to the parasite being present
in larger numbers in the former series of cases, (as an analysis of the symptoms
proved that all the cases were of the same nature), also supported very
strongly this explanation of the curves. In order to further test the question,
the figures of the monthly fever rate for the last ten years among the men
of the various regiments which were stationed in Doranda, together with the
monthly rainfall of the same period, were obtained, and the charts which
accompany this paper were worked out and have revealed several points of
interest which I propose to briefly point out in this communication.

   The upper diagrams represent the monthly number of admissions for
fever in the several years, while underneath them will be found the monthly
rainfall. It will be seen at a glance that, with the exception of the year 1892,
the great bulk of the fever occurs in the rainy season, and a closer examination
shows that, although the rains nearly always begin in June, the fever does not