4                                                                  PRECAUTIONARY MEASURES.
One attack does not exempt from subsequent attacks. This is established
by the personal experience of many medical officers. It is seldom possible to
obtain reliable statistical information on this point, as the intervals between
the epidemics have generally been long, and the survivors have been scattered
before another attack. The most authentic information on this subject is to be
obtained from the Indian jails. There were seven severe epidemics in the central
prison at Agra in the years 1851, 1856, 1860, 1861, 1862, 1863, and 1865. The
details of the two attacks in 1851 and 1856 were destroyed in the mutiny.  Those
of the five subsequent attacks have been carefully abstracted from the jail re-
cords. It is highly probable that many of the cases entered as Re-admitted during
the first year had been discharged before the poison was completely thrown
off, as they were only one or two days out of hospital ; but this objection
cannot apply to those re-admitted in subsequent years. Table No. I shows
that the proportion attacked is greater, but the mortality slightly less, in those
who had previously been attacked than in those exposed for the first time.*
The period of incubation varies according to the intensity of the poison
and the state of the recipient. In a small quantity it produces malaise, which
may pass off without active symptoms in two or three days ; but violent
symptoms with collapse may be induced by fatigue or purgative medicine. It
is generally during this stage that cholera is disseminated over the world,
particularly during pilgrimages in India. In some instances the recipient is
suddenly attacked whilst in contact with the affected. But in general there
is an interval of 12 or 24 hours after imbibing the poison before active symp-
toms appear. Two days are not generally exceeded ; but it is sometimes four
days before the disease shows active signs.
There is a marked coincidence, if no stronger connection, between the
season of the year and the appearance of the disease in most countries ; but
individual cases appear and the disease sometimes spreads at unusual seasons,
'It generally prevails in the warm and damp months ; but it has very frequently
raged during the hot dry winds of India, with a temperature of 120° or 130° F.,
and also in the cold frost of Russia with a temperature below zero. It prevails
most in level low lands ; but I have seen it at Landour and Simla, upwards
of 7,000 feet above the level of the sea.
During the rainy season in India, cholera occasionally assumes an inter-
mittent type, probably from the combined action of the cholera and miasmatic
poisons. The hour of attack is about 3 in the morning, and about the same
hour in the afternoon a change for the better or worse takes place. Profuse
cold clammy perspiration, like the sweating sickness of the dark ages, is the
characteristic of this form of the disease.
Cholera epidemics have been, most severe in cities, and in the parts of
onntonnients which are devoid of trees. There are several instances on record
where moving cholera camps into topes of trees was followed by marked benefit-
The subject is worthy of more attention ; but trees alone do not prevent
the dissemination of the disease, as it continued to prevail at Simla (which is
covered with trees) for several months in 1867. I have observed the immediate
cessation of attacks among the troops at Agra from crossing the river Jumna,
and several similar instances are recorded.
The severe attacks at Kurrachee in 1856, and at Peshawur in 1867, were
preceded by severe dust-storms with thunder. At Hurdwar, in 1867, and in
numerous other instances, the attacks have been preceded by thunder and rain ;
whilst in other instances the disease has subsided after severe storms ; but these
are not sanitary agents under our control.
PRECAUTIONARY MEASURES.
There are two or three advocates of the theory of the spontaneous gen-
eration of this specific poison from defective sanitary arrangements. This may
originate from observations limited to local outbreaks ; but it fails to explain
   The   table  shows  the  number  of oases admitted under the  separate heads of cholera and diarrhœa  and also  as
combined  under one heading,   which  I   consider conveys the   most clear   indication of the relative  sickness induced
and 304, or 2.752 per cent. Out of a strength of 11,046 during the five epidenies, 1.598, or 14.467 per cent., were attached
and 304, or 2.752 per cent. died. Out of 2,026 survivors of attacks, subjected to the influence of the disease during the
first and three  subsequent attacks, 296, or 14.610 per cent., were attacked, of whom 44, or 2.172 per cent., died