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of puckal work as a cause of the disease was not noted. We may, therefore, fairly
conclude that puckal work, as such, is only an indirect cause, and may safely continue
to be performed by the mules, provided the animals be not overworked at it and be
as much as possible prevented drinking water from the tanks.
22. Exposure to weather might predispose to attacks by lessening the constitu-
tional power or determine invasion by the parasites as implying plentiful access to
malaria, mud, stagnant water, bad food, and so on. I am led to consider exposure a
very powerful factor in production of relapsing fever. In Tonghoo especially the
mules working to and from Thandoun fell victims to the disease, for this work
implied an exhausting march first through terai, then up a very steep hill for about
nine miles, and finally insufficient shelter, food, and general care on arrival at Than-
doun. In the Rangoon Supply Depôt outbreak the disease was preceded by a period
of exposure during the height of the monsoon on the glacis of the pagoda and at Kokine.
Early in 1884 the Somersetshire mules were sent out into the districts to collect
straw, and they had hard work and a rough time of it in so far as I can make out.
I have evidence of some mules dying with ulceration of the stomach when on the line
of march to the frontier out-stations, but they possibly were suffering from the earlier
stages of the disease when they started. Death of two mules exposed on Anthrax
graves and of the hard-worked and exposed mules used for puckal work in the Somer-
setshire lines are evidences as to the effects of exposure, especially when combined
with overwork. We may say that in every case of outbreak exposure, with its usual
concomitants,—irregular food and water-supply,—has been operative previously. On
the other hand, with regard to overcrowding as a cause, we cannot admit that it has been
operative among the transport mules, which are exceptionally well housed and have
lots of room. And yet in this as in other enzootics (influenza, strangles, and so on)
we must admit that the aggregation of animals has some influence, for we have no
evidence that the disorder has prevailed as an enzootic among ponies kept in private
stables here, and we have certain evidence that it has not done so among mules and
ponies let out by the Transport on hire to Government officers.
23. Stables, either by being badly placed or in an unhealthy situation, or as being
deficient in protective influence on the animals housed in them, might tend to deter-
mine the appearance of relapsing fever. I can in almost all the cases which have
come under my notice trace the disease to exposure, but I can in addition find distinct
evidence that it also may occur from definite local centres or points. It is of great
importance in relation to prevention that we should trace the disease to these fomites
or local centres in order that we may avoid them in the future. The fact of the disease
being enzootic would indicate some local central operative influence in each outbreak,
and it has been attempted to point out that central influence in the consumption of
water from certain tanks, but we have seen that this view will not stand exact inquiry.
In the 1883-84 outbreak at Rangoon the supply depot mules and ponies mainly
suffered, only a few cases occurring in the outlying stables, those of the Native
Infantry and the British Infantry on either side at some distance away. In the
1884-85 outbreak we have had a great preponderance of cases in the British Infantry
lines, a very few in the depot, none in the Native Infantry or Sapper lines. An import-
ant matter to discuss is whether this decline in frequency of the disease from a centre
differing each year is due to the influence of air or locality. Advocates of the enzootic
wave theory might find here a fairly good argument in their favor, and say that in
1883-84 the disease wave struck against the northern side of the pagoda hill and was
diverted mainly to the west towards the Native Infantry lines, but slightly affecting
the British Infantry mules in the other direction, whereas in 1884-85 it came from
the south or east and thus struck on the east side of the hill and destroyed British
Infantry mules, but a few traces of the wave curled round the north side and thus
the depôt did not quite escape. We can very well understand that driving mist
could be a carrier of minute organisms and be diffused in consequence of the physical
conformation of the ground in the manner just mentioned, but we can hardly reconcile
with this view of conveyance of the contagium in air the facts that in 1883-84 the
sapper mules (thirty-five in number—a sufficiently large body to suffice as a test),
although living in a stable close by those of the Native Infantry, escaped; that D troop