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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last free to undertake the work. But now precisely occurred my last and most

annoying interruption.

Before coming to this, however, let us consider the results which had al-

ready been attained and which have been the basis of nearly all that has been

subsequently done.

(1) The general life-history of Proteosoma in the grey mosquito and the

mode of infection being now ascertained, we could foretell to a practical cer-

tainty that the life-history and mode of infection of all the other parasites of

the same group, including the human ones, would be closely similar in all

their stages; that is, that if they differed at all, they would differ only in small

details. The result of this was that if anyone wished to trace the life-history of

any of these organisms in a second host he would now find the task an ex-

tremely easy one, because (a) he would know exactly the appearance of the

parasite he was in search of, and (b) he would know exactly in what part of

the anatomy of the second host to look for it. And if he wished to ascertain

whether a given animal was or was not the second host of the parasite, he could

easily make sure of the fact by ascertaining whether or not it harboured the

described parasites, after feeding and dissection by the methods laid down by

me.

It is in fact solely by this means that we have been able to demonstrate the

proper hosts of the human parasites in many parts of the world.

(2) More than this, the pigmented cells of the aestivo-autumnal parasite of

man had been demonstrated to be exactly similar to those of Proteosoma on the

second, fourth, and fifth days after infection of the mosquito; and the hosts of

this important organism were shown to be at least two species of a special

genus which could be recognized by its possessing spotted wings and boat-

shaped eggs (section 23); and were clearly shown not to be my grey and

brindled mosquitoes, the former of which had been described sufficiently for

recognition

39,42

.

(3) The important law that not all species of mosquitoes can harbour a

given parasite of this group had been established, both with regard to the

aestivo-autumnal parasite and Proteosoma and Halteridium; and several im-

portant facts regarding mosquitoes had slowly become evident to me - but

were not published until later.

(4) Lastly full directions of technique had been given in my report

42

. These

consisted of numerous essential details, acquired during several years’ expe-

rience, regarding dissection and feeding, etc. - without a knowledge of which

the observer would be very likely to go wrong (as for instance by attempting

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to section his mosquitoes for searching for the parasites, and omitting to feed

them regularly and change their soiled habitations for clean ones).

On the other hand my researches had given little or no information about

the quartan and tertian parasites - except of course the all important analogy

with Proteosoma. The observation of the grey mosquito caught feeding on the

case of tertian was doubtful (section 14). Moreover they had not directly and

absolutely demonstrated the final stages even of the aestivo-autumnal para-

sites in the dappled-winged mosquitoes, nor the mode of infection. But never-

theless they had reduced the demonstrations still required to an easy formality

which was within the capacity of any tyro with sufficient material and a mi-

croscope.

I am sorry to have to write such a summary of my work as this one; but it

is rendered necessary by those who, during the long interruption of my la-

bours which now followed, were able to work out some details of the subject

before me, and who have wished to conceal the assured fact that their efforts

were simply a repetition and imitation of mine. It should be pointed out that,

by a generally recognized zoological rule, the discovery of the life-history of

Proteosoma 

in mosquitoes covers that of other members of the same group of

organisms, which have precisely the same development. By that rule, the right

of priority in discovery belongs to him who first works out the life-history of

one species of a group of animals; not to those who merely perform the easy

task of extending the known facts to other species. Discovery is discovery; the

determination of parallel facts, the filling in of details, the publication of pretty

illustrations, and the furnishing of formal proofs of matters which are already

certain, are useful - but do not constitute discovery.

My infection experiments on birds were completed early in August, and, as

will be related presently, I was now no longer able to defer my work on  kala-

azar. 

Consequently I was obliged to leave Calcutta on the 13th August for my

new duties - much exhausted by work and heat in the plains. Before doing so,

however, I released my host of little feathered prisoners, which had unwil-

lingly been of such assistance in the investigation.

It should be mentioned that from the first discovery of the thread-like bod-

ies I had wondered whether they have any other destination besides the sali-

vary gland. The eggs were especially suspected, but the results of investigation

were negative. I therefore now concluded that malaria is communicated only

by the bites of insects.

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