Ronald Ross Nobel Lecture

R E S E A R C H E S   O N   M A L A R I A

57

where in the induction. The disease was there, the mosquitoes were there -

how was it that I found nothing? I may perhaps be pardoned for dwelling on

my personal feelings during that time, and the astonishing time which fol-

lowed. Science too has its drama; and the actor on that real scene cannot help

being moved when he remembers it - although it may appear trivial enough

to others.

I had remembered the small dappled-winged mosquitoes, but as I could

not succeed either in finding their larvae or in inducing the adult insects to

bite patients, I could make no experiments with them. On the 15th August,

however, one of my assistants brought me a bottle of larvae, many of which

hatched out next day. Among them I found several dappled-winged mos-

quitoes, evidently of the same genus as those found about the barracks, but

much larger and stronger. Delighted with this capture I fed them (and they

proved to be very voracious) on a case with crescents in the blood. Expecting

to find more in the breeding bottle and wishing to watch the escape of the

motile filaments in this new variety, I dissected four of them for this purpose

immediately after feeding. This proved to be most unfortunate, as there were

no more of these insects in the bottle, and the results as regards the motile

filaments were negative. I had, however, four of the gorged dappled-winged

mosquitoes left; but by bad luck two of the dissections were very imperfect

and I found nothing. On the 20th August I had two remaining insects both

living. Both had been fed on the 16th instant. I had much work to do with

other mosquitoes, and was not able to attend to these until late in the afternoon

when my sight had become very fatigued. The seventh dappled-winged mos-

quito was then successfully dissected. Every cell was searched, and to my in-

tense disappointment nothing whatever was found, until I came to the insect’s

stomach. Here, however, just as I was about to abandon the examination, I

saw a very delicate circular cell apparently lying amongst the ordinary cells of

the organ, and scarcely distinguishable from them. Almost instinctively I felt

that here was something new. On looking further, another and another

similar object presented itself. I now focussed the lens carefully on one of these,

and found that it contained a few minute granules of some black substance

exactly like the pigment of the parasite of malaria. I counted altogether twelve

of these cells in the insect, but was so tired with work and had been so often

disappointed before that I did not at the moment recognize the value of the

observation. After mounting the preparation I went home and slept for nearly

an hour. On waking, my first thought was that the problem was solved; and

so it was.

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Next morning I returned to the hospital with much apprehension lest the

eighth and last dappled-winged mosquito should have died and become de-

composed during the night. It was alive; and was killed and dissected with

much anxiety. Similar bodies were present in it, only they were distinctly larger.

The seventh mosquito had been dissected four days after finding; the eighth

five days after feeding; the parasites in the latter had lived a day longer than

those in the former and were consequently larger. Both insects had been bred

from larvae in captivity; both had been fed for the first time on the same

person - a case of malaria; no such objects as these pigmented cells - as I then

called them - had ever before been seen in the hundreds of mosquitoes exam-

ined by me; the objects lay, not in the stomach cavity of the insects, but in the

thickness of the stomach wall; all contained a number of black granules pre-

cisely similar in appearance to those contained by the parasites of malaria, and

quite unlike anything which I had ever seen in any mosquito previously.

Lastly, these two mosquitoes were the first of the kind which I had ever tested.*

The mind long engaged with a single problem often acquires a kind of

prophetic insight, apparently stronger than reason, which tells the truth,

though the actual arguments may look feeble enough when put upon paper.

Such an insight is mainly based, I suppose, on a concentration of small proba-

bilities each of which may have little weight of itself; but in this case at all

events the insight was there and spoke the truth.

These two observations solved the malaria problem. They did not complete

the story, certainly; but they furnished the clue. At a stroke they gave both of

the two unknown quantities - the kind of mosquito implicated and the posi-

tion and appearance of the parasites within it. The great difficulty was really

overcome; and all the multitude of important results which have since been

obtained were obtained solely by the easy task of following this clue - a work

for children. We may rest assured that if these observations had not been made

we should still have remained ignorant of the mode in which this important

disease, with its annual death roll of millions, is propagated - aye, and would

have remained ignorant of it until some one else had taken up the same in-

vestigation by the same method.

And no other method would have solved the problem. It was necessary to

* On the assumption that these cells had developed from the motile filaments it was dif-

ficult at the moment to explain the pigment within them - as the motile filaments have no

pigment. I thought it possible, however, that after fixing themselves in the stomach wall

they might be able to derive haemoglobin from the contents of the organ, and afterwards

convert this into the pigment.

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