R E S E A R C H E S O N M A L A R I A
53
malaria at all. Hence, though I did not know it at the time, it is impossible to
indicate, much less to certify, the malaria-bearing species by its numerical rela-
tions with other species in malarious localities.
One of the principal results of my work in the Sigur Ghat was that it led me
to doubt the probability of infection by drinking water. I should have liked
to remain there much longer; but on the expiry of my leave was forced to
return to my regiment at Secunderabad, five hundred miles away, and was
never able to visit the place again.*
13. Secunderabad (1897). The fundamental discovery.
On my return to Secunde-
rabad (July 1897), the first thing I noticed was that the malaria had continued
unabated during almost two years since I had left; if anything it was worse,
and many recruits who had recently joined the regiment had been attacked -
as they averred, for the first time. This clearly showed that these cases were not
merely relapses, and that some cause of infection was actually at work among
the troops. It was for me to discover the cause; and I determined to return to
my old method, and to test experimentally all the kinds of mosquitoes preva-
lent anywhere near the barracks. I had now been studying the subject almost
constantly for over two years, and had become so very familiar with the mi-
croscopical appearance of the various structures of the mosquito** that I felt
the mosquito stage of the parasite could no longer escape me if it existed at all.
Numerous "cases of crescents" suitable for the experiments were in my hos-
pital, and it was obvious from the number of fresh cases occurring that the
proper kind of mosquito must be somewhere about. If I failed it could only
be because there was some flaw in Manson’s induction.
At the same time a possible fallacy was detected in the logic of that part of
the theory which suggested that the motile filaments after their escape from
the parent cells in the mosquito’s stomach must take up their abode in the tissues
of the insect. The vital and inevitable part of the induction consisted only of
the reasoning which inferred that the stomach of the mosquito is the natural
locus
for the escape of the motile filaments. It was only conjecture to say that
they must enter the tissues; because for all we knew it was possible that they
might remain in the intestine for some time and then be voided, probably in
some altered form, either upon the ground or upon the human skin (see my
* I had been offered an appointment in Berar, but had declined it in order to carry on
these researches in the Sigur Ghat. I suffered severely for this later on.
**
This does not mean that I was equally familiar with the macroscopical anatomy of the
mosquito - a subject which has only recently been dealt with fully.
54
1 9 0 2 R .RO S S
hypotheses in the previous section). It was therefore now necessary to examine
the evacuations as well as the tissues of my subjects.
I commenced work by making a careful survey of the various kinds of mos-
quitoes which were to be found in the officers’ quarters, in the regimental hos-
pital, and in the numerous little houses of the native soldiers, which consti-
tuted the barracks or "lines", as they were called. I found first, the insects with
which I was familiar during my previous studies here in 1895, namely (a)
several species of brindled mosquitoes, and (b) two species of grey mosqui-
toes. But at the same time I was astonished at observing that the whole place
was overrun by swarms of (c) a small and delicate variety of mosquitoes,
which were at once observed to rest with the body-axis at an angle to the
wall, and which had spotted wings. In fact they were evidently of the same
genus (though not of the same species) as the mosquito which had been previ-
ously found in the Sigur Ghat - a genus, or perhaps family, quite distinct from
those of the grey and brindled mosquitoes with which I had hitherto been
working.
It is now time to speak more particularly of all these mosquitoes.
I had writ-
ten repeatedly to Manson, to various booksellers in England, and to several
persons in India who I thought might help me, for some literature on the sub-
ject; but could obtain nothing except a few notes by popular authors, such as
Thomas, who wrote on piscatorial subjects in India. I could not even obtain
any adequate works on the anatomy of insects in general. Of Ficalbi’s work
on European gnats - which would have helped me immensely - I was igno-
rant, and received no copy. Manson had found the name of one species of
mosquito which I sent to him; but this did not help me, for what I required
was a scientific work on the structure and classification of the mosquitoes as
a group. I was therefore obliged, as mentioned in section 10, to trust to my
own rough methods of classification; and these were based, not on the criteria
of entomologists, such as the structures of the mouth parts or the nervures of
the wings, but on the general appearance and markings, the eggs, the habits,
etc., of the insects. It was only the working classification of an amateur with-
out literature to guide him, and made for his own convenience; but, as events
have proved it was roughly correct. Up to July 1897 I recognized the two
following groups :
(a) Brindled mosquitoes (
now recognized as belonging to the genus Stegomyia,
Theobald). Body and legs boldly marked black and white, or brown and
white. Wings plain. Biting voraciously, mostly in the day-time. Resting with
abdomen hanging towards the surface of attachment, and the last pair of