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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procedure.* We agreed that the proper course would be to select patients

whose blood was rich in gametocytes (the name now given to those forms of

the parasite of which some produce motile filaments); to allow mosquitoes to

bite these patients; and to attempt to trace in the tissues of these insects the

development of the said motile filaments (which we thought were flagellate

spores). In fact it was proposed that I should adopt exactly the procedure em-

ployed by Manson in regard to Filaria bancrofti. It seemed necessary only to

follow the motile filaments, after their escape from the gametocytes contained

in the ingested blood in the mosquito’s stomach, to their supposed destination

within some kind of cells of the insect’s tissues (e.g. the stomach or blood cells)

- apparently an easy task. It was true we anticipated, on the analogy of the

filaria, that not all species of mosquitoes would be amenable to the malarial

infection, and we recognized that this doubt would increase the difficulties;

but we hoped readily to distinguish the proper species by its particular preva-

lence in very malarious localities. The motile filaments being traced to their

habitat in particular cells of the insect, we thought that it would be easy to

observe their further development, and to watch their escape into water after

the host’s death. This done we should be able to identify the extra corporeal

form of the parasites in water, air, or dew, and to ascertain exactly the route

of infection of man.

8. Preliminary observations at Secunderabad (1895)

. I reached India in 1895 and

found myself appointed medical officer of a regiment of native soldiers sta-

tioned at Secunderabad and suffering much from malarial fever. A survey was

immediately made of the malarial parasites existing among these men and I

found myself able to confirm for India, in almost every detail, the specialized

work of the Italians and of Mannaberg.**

* We thought that Manson himself could not undertake the work in England, but this

perhaps would not have been as difficult as we supposed. The parasites have now been

cultivated in the local Anopheles at Hamburg and have been found in them in Holland.

Work might easily have been done in this direction at home, while I was labouring in In-

dia. At all events I should have been greatly assisted by a study of British gnats.

** My regiment was stationed near a small marsh and suffered badly, while another regi-

ment situated only a mile to leeward of the same marsh escaped. My regiment suffered

from the aestivo-autumnal and tertian varieties of parasite, quartan being quite absent;

but in the neighbouring regiments of this great garrison quartan abounded - a fact which

confirmed me in favour of the view that these varieties are distinct and not interchange-

able forms. The work of Crombie and myselfwas the first done in India on this basis, that

of Vandyke Carter (1887) being done on the basis of Laveran’s works.

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At the same time I examined the mosquitoes which abounded in the bar-

racks and hospital. Before leaving England I had made many attempts to ob-

tain literature on mosquitoes, especially the Indian ones, but without success

except for some brief notes in encyclopedias; and I did not even clearly

recognize the identity of mosquitoes and gnats, but thought that the for-

mer constituted a special division of the Culicidae.* Consequently I was

forced to rely entirely on my own observations; and I noted that the various

species of mosquitoes of the locality belonged apparently to two different

groups, separated by many traits, and called these groups for my own con-

venience, brindled mosquitoes and grey mosquitoes. It was not until 1897 that I

clearly recognized a third group which I called spotted-winged mosquitoes (see

sections 12 and 13).

As the grey and brindled mosquitoes abounded round the infected barracks,

it was naturally thought likely that they were concerned in the propagation

of the disease. After some initial difficulties I caused numbers of them (espe-

cially the brindled mosquitoes) to be fed on persons with the gametocytes of

aestivo-autumnal fever (crescents) in their blood. It should be noted that from

the first I employed for this purpose only mosquitoes bred in captivity from

the larvae, and not insects caught at random in the houses. There were two

excellent reasons for this; first, that the insects caught at random might have

already fed themselves previously and have thus, for all I knew, acquired va-

rious parasites which might confuse my results; and, secondly, because it is

easier to obtain the insects in numbers by collecting their larvae and keeping

them in vessels until they hatch out from the pupae, rather than by catching

each separately by hand. The mosquitoes were fed by being released from the

breeding-jar into a mosquito-net within which the patient was placed, the

gorged insects being subsequently caught in bottles and dissected as required.

From the first I kept careful notes of my observations, and also recorded

them in letters to Manson sent by almost every weekly mail, except when

later, being very busy at Bangalore, I was obliged to reduce both notes and

letters. The note-books and letters are still in my hands.

9. Secunderabad (1895). The motile filaments in mosquitoes. The first point re-

quiring study was the process by which the motile filaments escape from the

parent cells (gametocytes) within the stomach cavity of the mosquitoes. The

process had been frequently watched in vitro (in slides of liquid blood pre-

* In spite of repeated attempts to obtain such literature I remained in the same predica-

ment until I returned to England in 1899.

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