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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had determined to begin the enquiry at once at my own expense during two

months’ leave which was due to me; and accordingly, on the completion of

my duty in Bangalore, I went to the Nilgherry Hills for the purpose of study-

ing the point referred to in some of the intensely malarious plantations at the

foot of these mountains.

12. The Sigur Ghat (1897). I arrived at Ootacamund, the great hill station of

the Nilgherry Hills, at the beginning of April, 1896. This station which is

about 8,000 feet above sea-level, is surrounded by numerous tea and coffee

plantations, scattered here and there in the rich valleys of the hills, and even

for some distance out on the plains which encompass the hills like a sea. After

enquiry it was determined to begin the investigation in the Sigur Ghat, a long

natural trench which cuts at one stroke from the Ootacamund plateau right

down to the plain, and which had the worst reputation for malaria. A dâk

bungalow 

(rest house) and a small plantation existed near the top of the trench,

at a place called Kahutti about 5,500 feet above sea-level; and owing to the

fact that a single night spent lower down the valley was thought enough to

ensure a bad and perhaps fatal attack, I determined to lodge here and visit the

lower valley only during the day time. Nevertheless even at Kalhutti I found

almost everyone suffering from fever - which was ascribed to miasmata float-

ing up the ravine from the plains below; and I had been there only a few days

and had paid only one diurnal visit to the plain when I myself suffered a bad

attack of aestivo-autumnal infection, the diagnosis being confirmed by the

microscope.*

After two weeks’ energetic treatment with quinine I was well enough to

resume operations; and this time went direct to the plantations at the foot of

the Sigur Ghat. The owner of one of them, Mr. Kindersley, wise enough to

reside in the hills during the intensely malarious season of the year, very kindly

placed his house in the plantation at my disposal; so that I was able to make a

thorough survey of the locality. Both plantations are situated in the midst of

luxuriant forest and undergrowth close under the declivities of the mountains,

* This case was remarkable for the brevity of its incubation period. I had never suffered

before from malaria, and was not likely to have acquired the infection either at Bangalore

or Ootacamund. I had arrived at Kalhutti at 6 pm on the 22nd April, and my attack com-

menced at

 

10 p.m. on the 25th April. I ascribed it at the time to my visit to the plain made

on the 23rd April; but there is now little doubt that the infection was acquired at Kalhutti

itself, which was swarming with mosquitoes, and where the servant of the dâk bungalow

and all his family were ill. At the same time I do not remember to have been bitten by

mosquitoes, and said so in my published account.

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and are copiously watered by irrigation channels. Almost all the native em-

ployees, as well as some families of aborigines, were suffering from severe

malaria - anaemia, emaciation, and enlarged spleen; and the parasites were

easily found in the blood of some of them. But I was not a little astonished

when I discovered that mosquitoes appeared to be almost absent in all the

houses. In spite of considerable rewards which were offered for their capture,

and in spite of the efforts of my trained servants and myself, scarcely any were

secured. I was informed indeed by some of the employees that they were often

bitten at night by insects which escaped in the morning; but these nocturnal

visitors were not procurable      

*. Later however, we were told of some insects

which haunted the jungle and bit in the daytime under the trees. I found these

to be a small kind of brindled mosquito, and strongly suspected that they

might be the culpable species; and accordingly examined them closely and

called them Culex silvestris.

A part of my mission here was to enquire whether the mosquitoes in this

highly malarious spot did not contain parasites which were not contained in

the mosquitoes of the less malarious Bangalore. If they did so these parasites

might reasonably be suspected of being the mosquito stage of the malaria

parasite; and the question could subsequently be tested by experiment. These

mosquitoes were at once found to contain two new kinds of parasites, namely

crowds of active swarm-spores in the intestine, and, secondly, clusters of

spores (each cluster containing eight bright oval spores) in the ventral nervous

system. A close study was made of these organisms; but they did not appear

in some of the jungle mosquitoes which had been fed on patients. Strangely

enough, however, a person who volunteered to swallow a number of the

swarm-spores in water was attacked subsequently with fever, the malaria

parasites, however, not being found in his blood; but I heard afterwards that,

contrary to his statements, he had had fever just previously.

It will be remembered that Manson’s secondary hypothesis suggested that

the motile filaments, after living for some time in the mosquito, pass from it

into the water, and thence by ingestion or inhalation into man. My experi-

ence, however, tended to convince me that if such infection of water takes

place at all it must be very limited - in other words, that after their escape

from the dead mosquito, the organisms can neither travel far in the water nor

live long there. For if they could do this, almost all water in India would be

infected, and the disease would be universal, instead of being confined, as it is,

to certain spots. For the same reason the miasmatic theory never appealed

* Judging by our present knowledge, these must have been the offenders.

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