31
(b) Rainfall in relation to prevalence of the disease is thus far noteworthy that
both at Tonghoo in 1884-85 and at Rangoon in 1883-84 and 1884-85
the rain curve has been parallel to the curve of disease fatality but three
or four months antecedent to it. This is very striking {vide Graphic
Record No. 3) and suggests that the advent of the rains and the increase
and decrease of rainfall are in direct relation to the disease and probably
simultaneous with the occurrence of attacks, allowing some three months
for the average duration of cases (including incubation). The actual
amount of rain bears no relation to prevalence of the disease, for the fall
was greater in Tonghoo in 1883-84 when the disease did not prevail than
in 1884-85 when it proved extremely fatal, and the total losses in the
two years have been about equal in Rangoon, whereas the current
season has been much wetter than that of last year. The rainfall of
Thayetmyo, hitherto a disease-free place, is very low as compared with
that of Rangoon and Tonghoo. It is plain that increase of average
monthly rainfall means increase in the number of swamps and marshes,
whereas increase in the total amount falling in the season or abnormally
large rainfall at one time means increased dilution of tanks and flushing
of natural water channels. We can to an extent understand why the
Relapsing Fever should be in association rather with the gradual annual
rise and fall of the rain curve than with unusually severe downpours.
(c) Humidity of the atmosphere holds the same relations to the disease as rain-
fall.
(d) Temperature.—In so far as we can judge, the disease is associated in its
invasion with high minimum temperatures and low maximum, and it is
on the decline when the range of temperature daily is greatest. We
cannot, therefore, associate it with either excessive cold or excessive heat.
It seems that exposure does not act through reduction of resisting power
by the influence of extremes of temperature nor excessive diurnal range.
These influences must affect the strength of constitution ; but here, again,
we have evidence that condition and constitutional resisting power have
but little effect for good or evil in this disease.
26. In considering the influence of season, it will be well for a moment to
compare the prevalence of fevers, cholera, and small-pox of man with that of relapsing
fever. We shall hereby be enabled to an extent to decide whether the seasonal
influences in relation to relapsing fever of mules are special or only such as are operative
in disease in general. The conclusions at which we arrive from this method of inquiry
are that the fatalities from relapsing fever in mules occur in no direct association
with the general unhealthiness of the season. In 1884 it prevailed contemporaneously
with cholera, possibly as both diseases are affected by water-supply {vide Chart No. 5.)
27. Water-supply.—I have already shown that we can never thoroughly rely on
information as to the sources of drinking water-supply for transport mules. The
main facts with regard to the outbreaks are as follow:—At Tonghoo all the regi-
mental mules are, out in the sanitary camp, and have been, in the lines, watered from
wells. The water from these, although somewhat opalescent, cannot be considered bad.
Water also, as far as we can judge, is not a likely source of the disease at Rangoon.
The Somersetshire mules have (officially) been watered only from the Royal Lakes and
certain wells during the time when the disease can have been conveyed to those which
have succumbed to the current outbreak. The water of the Royal Lakes is very good,
as is also that from the wells. The latter are two in number—one on the high ground
of the plateau, near the hospital latrine, used for troops A and C, and the other
near the Cemetery road on the low ground near the native followers' village. They
are both covered. The upper one especially is liable to run short of water, on
occurrence of which emergency the animals are taken to the Royal Lakes to drink.
I do not think the water-supply of the Somersetshire mules has been at all to blame
for this outbreak, nor do I attribute the disease at Tonghoo to that source.
I quite agree with my predecessors in this inquiry that water in general, and from
tanks in particular, is always open to suspicion in causation of this disorder, but I
think it most often acts as such when obtained out of the ordinary routine, as when