Ronald Ross Nobel Lecture

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

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together with plenty of leisure, I was now progressing excellently with my

researches (though without definite results) when I received my first interrup-

tion. On the 9th September 1895, I was placed on special duty by the Govern-

ment of India to combat a serious outbreak of cholera in the large town of

Bangalore, and also to report on the general condition of sanitation there. This

duty was of great interest and value to me because it afforded me an unrivalled

opportunity for examining in the closest detail the general sanitation of a

tropical city - an experience which has stood me in good stead during later

years. For four months, however, I was so busy with my new labours that I

had little time for research. Bangalore I already knew well, having indeed

made some of my first studies of malaria there when staff surgeon of the town

from 1890-1893. I now easily ascertained by the light of Laveran’s great dis-

covery that the cases of fever which I had attributed to intestinal auto-intoxi-

cation were nothing but examples of aestivo-autumnal infection among par-

tially immunized natives. I found also that, as at Secunderabad, my brindled

and grey mosquitoes abounded all over the place. I dissected a few mosquitoes

as time allowed; and when my more arduous sanitary duties began to dim-

inish in March 1896, I found that I could give an hour or two a day to the

work. My results, however, remained constantly negative, in spite of the

closest scrutiny of many mosquitoes. At the same time I continued my at-

tempts to produce infection by water.

In March 1896, Manson delivered the three Goulstonian Lectures at the

Royal College of Physicians in London, and again put the case of his hypoth-

esis in an admirable manner, supporting his arguments largely upon my ob-

servations of the previous year

2 6

. He wrote to me frequently for fed mos-

quitoes, which I sent to him whenever I could. He also urged me to keep on

the track of the flagellated spores; advised me to try infection experiments

with the insufflation of dried and powdered mosquitoes, and with the vapour

of an "artificial marsh" in which fed mosquitoes had died. These devices did

not appear as promising to me as they evidently did to him. It was scarcely

likely that dead mosquitoes could do much in regard to the dissemination of

malaria in nature, at least in the form of dust, owing principally to the fact

that dead insects seldom escape the ants in the tropics. All dust, moreover, is

generally subject to the intense heat of the sun which, except in the presence of

water, must be very inimical to most unprotected organisms. The small

amount of time at my disposal was therefore devoted to the methods already

attempted.

Towards the middle of the year I had made nineteen experiments with a

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   1 9 0 2  R .R O S S

view to carrying infection by drinking water; and together with three more

cases, I described these in a publication at the end of the year

30

. Water, in

which mosquitoes fed on cases of malaria had died, or which contained large

numbers of the pseudo-navicellae of the gregarines of mosquitoes, was given

to various persons by the mouth. The majority of the attempts were entirely

negative: but nevertheless a slight but noticeable reaction did occur in three

of the whole number of twenty-two cases. This still remains a very curious

circumstance; but the facts were published exactly as they were found, with-

out the influence of the "personal equation". At the end of the paper I sum-

marized my results and decided that the positive reactions, though interesting,

were too few and too slight to warrant any definite conclusion.* I am now

inclined to think that they may have been due to the following circumstances.

The persons on whom the experiments were made were generally low-caste

indians who required a fee before drinking the water and also an assurance

that they would receive more if taken ill. Now it is well recognized that many

natives are constantly infected with malaria and get relapses on any extra-

ordinary demand being made upon their systems, as by fatigue, chill, or dissi-

pation. I have even heard it stated by medical men possessing large experience

of natives that they can often produce fever in themselves by exposure when

they wish to do so. In this case at all events it was possible that some of the

subjects spent their preliminary fees in dissipation, thus producing the sup-

posed reaction after the experiments.

These results not being as decisive as I had expected from the first experi-

ment of the kind made in the previous year, I began to consider whether some

other route of infection was not possible or probable; and it soon grew upon

me that Mansons’s induction was exigent only as regards the entry of the

parasites into mosquitoes, and that his secondary hypothesis regarding their

escape from the insects and their infection of man through drinking water

was not so strong. I quickly thought of several other routes for infection -

which will be examined presently; and first I considered it possible that the

insects, previously infected from diseased persons or possibly from other mos-

quitoes, might then inoculate the parasites into healthy persons during punc-

ture, or might deposit them on the skin during haustellation. It was easy to

*My actual words were, "While we cannot dream of stating definitely on the strength

of these experiments that there is something connected with the mosquito which is capa-

ble of imparting fever, the three positive results are still curious and tend to be in favour of

the truth of Manson’s theory." Yet one of my Italian critics has attempted to prove, by

ignoring this passage, that I pretended to have established infection by drinking water.

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