Ronald Ross Nobel Lecture

    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.

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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

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