4
Dirt, especially " floor filth " generally of the moist organic variety so largely
found in the surroundings and interiors of eastern houses, offers the most
favourable pabulum for the nourishment of the microbes.
The cowdung floor, so commonly seen in Poona, should be abolished, were
it possible, and all floors raised above the ground, allowing thus a free current
of air beneath.
Influence of Temperature.
The climatic influence for its development and continuance are various.
Although a hot moist climate, with a temperature from 75° F. to 90° F. is
favourable for the development of the bacillus, as shown by experience and ex-
periment, yet the domestic conditions under which the people live has probably
much more influence. The domestic condition which influences the spread of
plague is the herding together of large masses of people in badly ventilated
houses, the want of light and sunshine, and the preparation of food in these
confined spaces. An increase of the death-rate in an epidemic usually follows
wet or cold weather, and the explanation is purely physical and not meteorolo-
gical. These alterations in climate usually drive the people to seek the
shelter of their houses where there is a far greater probability of their being
infected with the disease.
The accompanying chart * shows the relation of the temperature to the total
mortality during the epidemic of plague in the City of Poona from December
27th, 1896, to May 20th, 1897.
I am indebted to the Director of the Yerrowda Observatory for kindly
supplying the daily maximum and minimum temperatures for that period.
For convenience the means of five-day periods are adopted, and allowing for
a probable five-days' incubation period the temperature curve starts one period
previous to the mortality chart, to allow for five days effect of temperature.
The mortality curve is traced in yellow, the temperature in blue.
Up to the 2nd week in March, there is with rise in temperature a corre-
sponding rise in the total mortality. From the 22nd to 26th March, with marked
fall in temperature, there was arise in the mortality. With the rise in tempera-
ture after period (18) there is a steady fall which might, with the upward curve
in temperature, have carried some weight as to the influence of a rise in heat,
but for the fact that the operations conducted against the plague by aid of the
military were started on March 13th, a few clays after which their influence
began to be felt, when a steady marked and permanent fall in the mortality
curve set in. Up to now, June the 13th with fall in temperature, seven days of
damp and rain, there has been no recrudescence.
Temperature then, as far as fluctuation in a district shows, evidently has no
relation to the disease.
Conveyance of Infection by Animals.
Certain species of animals are liable to infection by plague, the Rodentia
more especially. Dead rats are undoubtedly a frequent concomitant of plague,
and many look upon them as precursors of the disease ; this is, however, probably
not so ; but rats would naturally fall early victims, as they are inhabitants of
the ground and also ground feeders. The presence of dead rats is a valuable
indicator pointing to the infection of a locality. To what extent rats, mice,
&c., may act as conveyors of the disease is a moot question.
The bacillus is found in all the organs of the rat's body, in which it is found
in the human subject. It is possible that the infection is more acute in animals,
as in rats and mice the characteristic bacillus is found a few days after infection
on post mortem examination ; whereas in the human subject you find rather
more an involution form of the bacillus than the characteristic one.
The excreta of infected rats have been found to contain the bacillus which
would infect a dwelling-house and so convey the contagion to the inhabitants.
The rats in Poona were not in excessive numbers, but many were found dead
of plague as is mentioned in my Memorandum on Disinfection.
However slight the probability of the spread of the disease by this mode of
infection, it is certainly desirable to kill all rats possible and to burn the bodies
of the dead ones.