Ronald Ross Nobel Lecture

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find not one but two unknown quantities, and neither could be found by it-

self. There are no phenomena which would serve to indicate the kind of mos-

quito. In nearly all malarious places there are many kinds of mosquitoes, and,

as in the Sigur Ghat and other places, the malaria-bearing species are in no

way predominant among them either in numbers or in any other way. Indeed

the malaria-bearing species occur in places where malaria has not been known

in the memory of man, as around Liverpool. By what process of reasoning

then could we isolate the species? It might possibly have been practicable to

detect it by a very long series of experiments aimed at infecting men by the

bites of successive species of mosquitoes; but no one would have undertaken

such a work without the guide of a very strong theory in favour of inoculation

by the bite; and the theory of King and Bignami to this effect was little more

than a conjecture. It was not likely that the first species tried would have given

successful results, as my own experiments of 1896 showed. Even if, after a

multitude of costly and dangerous experiments, a positive result had been at-

tained by this method, it would always be open to doubt (seeing that the

experiments would have to be done in a malarious country) whether the case

was not merely one of relapse; and another long series of experiments would

be required to eliminate this doubt. And then, even when the proper species

of mosquito was detected, there would still be no guide to the form and posi-

tion of the parasites within it, or even to the way in which they enter the insect

(Bignami thought that they enter the larvae from marsh water). No, the thing

was not practical. Bignami himself abandoned his experiments on his own

theory after the first failure

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and did not resume them until after my work

had clearly indicated both the kind o  mosquito implicated and the route of

f

infection. The only practicable method was to attempt to find both unknown

quantities simultaneously by the "trial and failure system" - such as I adopted.*

The discovery of the pigmented cells, therefore, ended for me at least the

old research, the period of doubt, the groping in the dark. The secret spring

had been touched, the door flew open, the path led onward full in the light,

and it was obvious that science and humanity had found a new dominion.

But it was necessary to follow the clue forthwith; to watch the development

of the pigmented cells in mosquito after mosquito; to ascertain what became

of them; to fathom the mystery of the route of infection; and then to save

human life in the gross, perhaps to open continents to civilization.

* I mention these facts because many writers on the subject seem to think that the original

discovery was made merely by catching the first mosquito and finding the pigmented

cells within it.

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The first thing was to obtain more - hundreds - of these large dappled-

winged mosquitoes. Alas, the man who had found them had, contrary to my

orders, put the larvae from many sources in the same bottle! All the larvae

from all these sources were collected - but no more dappled-winged mos-

quitoes! I turned then to the small but similar variety which swarmed about

the barracks. Being evidently of the same genus, they too would probably

harbour the parasites; but though my men and myself searched high and low

for their larvae, we could not find them. I could scarcely even persuade the

adults to lay their eggs in captivity.

Thinking that in spite of all my care I may have overlooked the pigmented

cells in the grey and brindled mosquitoes, I now searched for them in the

stomachs of a number of these, but without result. A number of the small

dappled-winged mosquitoes caught about the hospital were also examined

for them in vain. These observations served however for a "control" on the

two positive cases.

Owing to the great heat at Secunderabad I had been obliged to leave my

family at Ootacamund, and was now compelled to go to Bangalore for a few

days in order to settle them there for the remainder of the summer. This gave

me leisure for writing a report to the government of India on the discovery of

the pigmented cells, and also a short paper on the same subject for publication.

The latter was of course intended only as a preliminary to a detailed report

which I hoped to be able to publish in a few months and which I thought

Fig.2. Pigmented cells (zygotes) of aestivo-autumnal parasite in dappled-winged mos-

quitoes (Anopheles). From  Ross’s paper, British Medical Journal, 18th Dec. 1897, p. 1787.

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would contain the full explication of the whole problem. I described my

method in a few opening lines, being careful to note that the mosquitoes used

by me had been "bred in bottles from the larva". The mosquitoes were then

described as well as possible - the spots on the wings and the peculiar shape of

the eggs being noted, but reference to the peculiar attitude being inadvertently

omitted. Next I gave in detail the circumstances under which the pigmented

cells were found, together with a description of them; and finally discussed,

very guardedly, their probable relation to the parasite of malaria. I had

brought the original preparations with me, and now showed them to my

friend Surgeon Major John Smyth, who at my request kindly added a note to

my paper, corroborating my description. They were then despatched by post

to Manson. My paper, however, did not appear until December

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; but when

it did so it was accompanied by an excellent drawing of the pigmented cells

furnished at the instance of Manson, and also by remarks of Manson, Bland

Sutton, and Thin, who discussed the new objects - the last holding that the

cells were ordinary cells of the stomach wall into which malarial pigment had

entered in some manner from the stomach cavity. This preliminary article

was published by me for the express purpose of guiding the researches of

others; and in fact anyone who had read my description of the pigmented cells

and of the dappled-winged mosquitoes would now have had little difficulty

in repeating my work.*

On my return to Secunderabad I was much disappointed to find that the

larvae of neither the large nor the small species of dappled-winged mosquito

had yet been collected. Consequently in the intervals of searching for them,

I spent my time in examining the stomachs of all the mosquitoes I could catch

for the pigmented cells. I hoped especially to find them in the small dappled-

winged insects caught about the hospital, where there were several cases of

malaria, but was disappointed. On the 18th September, however, a large grey

mosquito was observed feeding on a patient suffering from the benign tertian

parasites and was promptly secured. The stomach was full of black blood, so

that it must have fed previously (freshly imbibed blood showing red in the

insects) as well as on this occasion. It was kept until the 21st and was then

dissected. To my delight the pigmented cells were again found, in consider-

able numbers; but they were larger even than those of the mosquito of the

21st August. As this particular insect had not been bred from the larva in cap-

tivity I could not say for certain where it had become infected, but I thought

* This is exactly what was done by the Italian observers fifteen months later (see sec-

tion 23).

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