2
Inquiry was also instituted among ship-owners regarding any noticeable
mortality among rats on ships trading with China and ports where plague was
known to have existed, but in this case also with negative results. As the
outbreak commenced near the Docks, it appears most probable that the infection
was introduced by sea and carried in their clothes or goods by traders* who were
themselves insusceptible. It is also possible that it may have been introduced
in this way by traders from Northern India, as plague is believed to be endemic
on the southern slopes of the Himalayas.
The disease probably commenced to spread in Bombay about the beginning
of August 1896, as the mortality of the city began to increase in the second
week of that month (vide Table VII). This increase in mortality was attributed
at the time to remittent fever and lung affections, but as rats were dying in
great numbers in Mandvi Ward,-whore the death-rate among the population was
unusually high and where the prevalence of the epidemic was first discovered,
there can be little doubt that the excessive mortality was due to plague. The
epidemic spread slowly, and the total mortality continued to increase until by
the second week in February the whole city had become infected. After that
timo the mortality began to decrease, and by the end of May it had fallen to the
normal and deaths from plague ceased to occur.
The official returns of deaths from plague aro for various reasons not very
accurate. A fairly correct estimate of the mortality can be obtained, however,
by taking as plague mortality the difference between the weekly mortality
and the mean of the corresponding weeks during the preceding five years (vide
Table VII), as there was no other unusual cause of sickness present.
It must be remembered that the average weekly mortality during the
preceding five years is taken on a population of 800,000, and that, owing to the
exodus which occurred after the outbreak of the epidemic, the population was
reduced by from a fourth to a third of that number. The true incidence of the
disease was consequently considerably heavier during the later weeks than
shown in the table, and this error is a gradually increasing one growing with
the decrease of the population.
It has been stated that in other places outbreaks were often preceded by
the appearance of cases of painless buboes unaccompanied by vomiting, fever,
headache or other symptoms of plague, but this was not observed in Bombay.
It may here be noted that the great difficulty which arises in tracing the
mode of infection and the course of plague as compared with the other more
common infectious diseases is due to two facts—viz., that animals such as rats
readily contract and afterwards spread the disease, and that the microbe is capable
of thriving and multiplying outside the animal body, as is seen, for example, when
it is cultivated in broth or on ghee. It is evident that infection may be carried
by rats to persons who have never been brought into contact with plague
patients, nor with persons visiting plague patients, and whose food and clothing
could not have been contaminated in any other way. On the other hand the
germs may bo convoyed by persons who are themselves insusceptible to plague,
and, having grown and multiplied on suitable media and under favourable condi-
tions, may infect large numbers of people who have never come into contact with
plague patients, their attendants or plague-stricken rats.
The development of plague in an epidemic form was believed by many per-
sons to be duo to rotten grain which had been buried underground, and it was
thought by some, infected with plague germs. Had rotten or diseased grain
been sold as food (and there was no evidence that this took place), it would in
all probability have given rise to digestive disorders, and in so far have predis-
posed to plague ; but if the grain had been infected with plague bacilli, the disease
would have appeared in several localties simultaneously, wherever the infected
grain had been eaten. It is impossible to believe, too, that large stores of
infected grain could have been sold without giving rise to an outbreak of disease
* Dr. Jan Mahomed's first casos occurred towards the end oí September among Mooltanis
who trade with China, and who lived near the docks.