81
CHAPTER VI.
BRIEF SURVEY OF THE FACTORS WHICH INFLUENCE
MALARIA IN BOMBAY.
208. A consideration of the facts that have been discussed in the fore-
going chapters indicates that there is no direct relation between the climatic
conditions of Bombay and the occurrence of malaria, for though the climate
in every part of such a small island must be almost identical in character,
malaria is prevalent in some parts and almost absent in others. Neither is it
possible to trace any relation between the soil and malaria for a similar
reason. No relation can be traced also between cultivation and malaria in
Bombay, for where there is most cultivation there is least malaria and the
existence of rice lands and palm groves in the north of the island has not
rendered these parts malarious. As has been previously pointed out, the
low-lying, undrained and swampy part9 of Bombay are less malarious than the
parts that have been longest drained and that as a rule are not liable to flooding
and it follows that little direct relation can be traced between the height of
sub-soil water and malaria in Bombay.
209. Thus in Bombay malaria presents a complete contradiction to many
of the commonly accepted generalizations regarding the disease. But on the
other hand when the presence of malaria-carrying anopheles and their breeding
places are carefully enquired into, it is seen that there is a remarkable
correspondence between them and the presence of malaria on the island.
210. Nowadays the terms "malarious country" and "malarious
climate " are not really accurate and their continued use gives rise to a certain
amount of confusion in the minds of those who do not realize that, when a place
or climate is spoken of as being malarious what is really meant is that, many of
the people are infected with malarial parasites and that conditions are suitable
for the existence of species of mosquitoes capable of carrying the disease.
211. As malaria is due to the presence of a minute animal parasite which
passes one stage of its existence in the blood of man and another in the body of
a female anopheles mosquito of a suitable species, the occurrence of malarial
disease in any place is dependent upon the presence of the three factors :
(A) Man,
(B) The malaria parasite,
(C) A suitable species of anopheles,
and in general it may be said that the severity of malaria depends upon the
numerical relations of these different factors.
212. Broadly speaking it may be said that in malarious places the effect
of the disease among the population is proportionate to the number of malarial
parasites actually present. If there are only a few million parasites distributed
among a thousand people, there will be only a few cases of mild malaria,
whereas if the total number of parasites is many million times greater both the
number of sufferers and the severity of the cases will be proportionately
increased.
213. The number of malarial parasites present in a community tends to
increase or decrease under certain conditions.
(1) The presence of a large number of anopheles mosquitoes of a
species capable of carrying malaria tends to produce an increase in the
number of parasites owing to the spread of infection, whereas a reduction
in the number of suitable anopheles tends to produce a fall in the total
number of parasites due to a lessened spread of infection.
B 1S6—21