5
As a rule the rats on being attacked come out of their holes and, after
running around with staggering gait and roughened coat, die rapidly; they
also die in their underground retreats, below floors or in drains, their rotting
carcases being thus a fresh nucleus for infection.
Plies have been credited with carrying the disease, and one observer has
stated that the bacilli have been found on their wings and also in the intestines
of mosquitos ; yet it is a notorious fact that although nurses and attendants
on plague cases have been freely bitten by mosquitos or approached by flies
which have been feeding on plague patients, the percentage of plague amongst
them has been very small.
I believe that dogs and cats are exempt from the disease, and it is improb-
able that birds are ever attacked.
Influence of Clothing and Other Fomites.
The evidence of infection by clothes is conclusive. It is well known how
an Asiatic will treasure up any old rags ; and in Poona nearly every house
contained a large collection of a most filthy kind, and in many cases mats and
clothing, soiled by excreta from a plague patient, were found also to be treasured
up, eventually to prove a source of further contagion. In every case all rags
and also all clothes and bedding used by the sick were at once burnt. It is a
well-recognised fact that infected old clothes and old rags are an important
means of spreading the disease from town to town, as here the bacillus finds
a suitable breeding ground. One of the essential points in combating the spread
of the disease is the absolute disinfecting or better still the burning of the
clothes worn by the affected person, and the prohibition of exportation of rags,
hides and other articles in which the bacilli can find a favourable nidus from
the infected areas.
No pronounced opinion can be given as to the effect of clothing on the
susceptibility to the disease, but the immunity enjoyed by Europeans is remark-
able ; in this case other influences, such as better attention to hygiene, environ-
ment, food, &c., may affect the result. There can be little question that a
naked state of the feet and limbs must largely increase the danger of infection
by inoculation.
The Period of Incubation.
To determine the period of incubation in any disease is always one of
extreme difficulty, as there are so many points in any case open to question, and
it is rarely that the time can be decided upon to a certainty. There is, however,
no reason from experience in the recent epidemic of plague in Poona to alter
what has already been decided upon as the period of incubation in plague, namely,
from 2 to 10 days.
From the 3rd to the 5th day is probably the period in which the greatest
number of cases show the typical signs of the disease, The limit has usually
been put down at 10 days, and for all practical purposes, such as quarantine and
segregation, this is a reasonable and safe limit. An unmistakable case of in-
cubation, however, is quoted by Wilm, the disease showing itself 15 days after
the patient had been committed to a prison, which was free of the disease and
without likelihood of any outside infection. Such a lengthened period of in-
cubation must, however, be looked upon as extremely rare.
From experience gained in the Government Segregation Camp, where over
3,400 people passed through, who had been exposed to infection, the period of
10 clays segregation was found to be sufficient. One case occurred on the 11th
day on discharge and two on the 10th. These cases cannot be looked upon as
forming a period of incubation, as there still remains the possibility of infection
having taken place in the camp, although every possible precaution, such as the
immediate disinfection of all clothing, bedding, &c., vacation and disinfection of
the infected hut, and isolation of the cases and members of their families as
they occurred, was always strictly observed ; the following case, as having some
bearing on the period of incubation, may be quoted :—
B 1215—2