56 
THE TROPICAL AGRICULTURIST. 
[JuLv ], 1899. 
tates there, and if I go I shall make a d^tonv 
to some of the West Indian Islands, if I can 
af¥ord it, and see their cacao there, and may 
have some information for yon. 
"I was reading a pamphlet on Vanilla cul- 
ture in the Seychelles, published recently by 
the U.S. Department of Agriculture,* and 
will write some notes and send them by 
next mail if I can : you may find them of 
interest to your constituents. , , , , 
"It is a healthy sign to my mmd that at 
home just now the two most important 
questions interesting the nation are the pre- 
servation of the 'day of rest'— one day in 
seven— and the battle against Romanising and 
ritualistic tendencies in the Church. The Sun- 
day Daily Mail has given way before the 
weight of public opinion and stopped issue. 
MALARIA : MAJOR RONALD ROSS ON. 
The following is the text of the Report lately 
submitted by Major Ronald Ross, I. M.S., on his 
special investistations into malaria parasites :— 
I have the honour to address you, on completion 
of my term of special duty for the investigation of 
malaria, on the subject of the practical i-esults as 
regards the prevention of tbe disease which may 
be expected to arise from my researches : and I trust 
that this letter may be submitted to Government, 
if the Director-General thinks fit. 
MOSQUITOES AND MALAEIA. 
It has been shewn in my reports to you that the 
parasites of malaria pass a st«ge of their existence 
fa certain species of moequitoes, by the bites of which 
they are inoculated into the blood of healthy men 
and birds. These observations have solved the pro- 
blem— previously thought insoluble— of the mode of 
life of these parasites in external nature. My results 
have been accepted by Dr. Laveran, the discoverer of 
the parasites of malaria; by Dr. Manson, who ela- 
. borated the mosquito theory of malaria ; by Dr. 
Nuttall of tbe Hygienic Institute of Berlin, who has 
made a special study of the relations between 
insects and disease; and, i understand, by M. 
Metchinkoff, Director of the Laboratory of the Pasteur 
Institute in Paris. Lately, moreover Dr. C. W. 
Daniels of the Malaria Commission, who has been 
sent to study with me in Calcutta, has conhrmed my 
observations in a special report to the Boyal Society ; 
while, lastly, Professor Grassi and Drs. liignami and 
Bastianelli of Rome have been able, after receiving 
specimens and copies of my reports f rom me, to repeat 
my experiments in detail, and to follow two of the 
parasites of human malaria through ail their stages in 
a species of mosquito called the Anopheles Claviger. 
It may, therefore, be finally accepted as a fact that 
malaria is communicated by the bites of some species 
of mosquito ; and to judge from the general laws 
- Koverning the development of p.^l•asltlc animals such 
as the parasites of malaria, this is very probably the 
- onlv way in which infection is acquired, in which 
, opinion, several distinguished men of science concur 
^'l^ ransidering this statement, it is necessary to 
remember that it does not refer to the mere recnr- 
rences of fever to which people previously infected are 
■ often Hubiect as the result of chill, fatigue and so on. 
When I say that malaria is communicated by the bites 
' of mosquitoes, I allude only to the original infection. 
It is also necessary to guard against assertions to the 
effect that malaria is prevalent where mosquitoes 
and gnats do not e.xist. In my experience, when the 
- facta come to be enquired into such asser ions are 
found to be untrue. Scientific research has now 
yielded so absolute a proof of the mosquito theory of 
malaria that hearsay evidence opposed to it can no 
longer carry any weight. 
' * Quoted in Xfopml /igriQulUirist-'Ev, T,A, 
PBACTICAL KBMEDIEB. 
Hence it follows that, in order to eliminate 
malaria, wholly or partly . from a given locality, 
it is necessary only to exterminate the various 
gpecifis of insect which carry the lufic. ion. This 
will certainly remove the malaria to a large extent 
and will almost certainly ren-fve it . altogether. It 
remains only to consider whether such a measore 
is practicab'e. Theoretically tlie extermination of 
moEqaitoes is a very simple matter. These insecfs 
are always hatched from aquatic larva; or grubs which 
can live only in small stagnant collections of water, 
such as pots and tubs of water, garden cisterns, 
wells, ditches and diains, small pond?, half-diied 
watet-coiires, and temporary pools of rain water. So 
far as I have yet observed, the larvag are seld^Mi 
to be found in larger bodies of water, such as tauk^, 
rice fields, streams and river.', and hiUes, because In 
such places they are devoured by minnows and olher 
email fish. Nor have I ever seen any evidence 
in favour of the popular view that they brcei in damp 
grass, dead leaves, and so on. He ice in order to 
get rid of these insects from a locality, it will suf- 
fice to empty ont or niain away or treat wiili cer- 
tain chemicals the small collections of water in which 
their larvas must pass their existence. But the 
practicability of tbis will depend on circum- 
stances — especially, I think, on the species of mos- 
quito with which we wish to deal. In my experience, 
different species select different habitations for tlieir 
larva3. Thus the common "brindled mosquitoes" 
breed almost entire!}' in pots and tubs of water ; tbe 
common " grey mosquitoes " only in cisterns, ditches 
and drains; while the rarer " spotted-winged mosqui- 
toes " Roeni to choose only shallow rain-water puddles 
and ponds too large to dry up under a week or more 
and too small or too foul and stagnant for minnows. 
Hence the larvae of the first two varieties are found 
in large numbers round almost all human dwellings in 
India ; and, because their breeding grounds — namely 
vessels of water, drains and wells — are so numerous 
and are so frequently contained in private tenements, 
it will be almost impossible to exterminate them on a 
large scale. On the other hand, spotted-winced mos- 
quitoes are f;enerally much more rare than the other 
two varieties. They do not appear to breed in weli.s, 
cisterns and vessels of water, and therefore have 
no special connection with liuman habitations. In 
fact, it is usually a matter of some difficulty to 
obtain their larvs; Small pools of any permanence 
— such as they require — are not common in most 
parts of India, except during the rains, and then 
pools of this kind are generally full of minnows 
which make short work of any mosquitoe larvaj 
they may find. In other words, the breeding 
grounds of the spotted-winged varieties seem to be so iso- 
lated and small that I think it maybe possible to exter- 
minate this species under certain circumsta.nces. The 
importance of these observations will be apparent 
when I add that hitherto the parasites of liuman 
malaria have been found ouly in spotted-winged 
mosquitoes — namely in two species of them in India 
and in one species in Italy. As tbe result of very 
numerous experiments I think that the common 
brindled and grey mosquitoes are quite innocuous as 
regards human malaria — a fortunate circumstance for 
the human race in the tropics. And Professor Grassi 
seems to have come to the same conclusion as the 
result of his enquiries in Italy. 
WORDS OF CAUTION. 
But I wish to be understood as writing with all 
due caution on these points. Up to the present our 
knowledge, both as regards the habits of tbe various 
species of mosquito and as regards the capacity of 
eich for carrying malaria is not complete. All I can 
now say is that if my anticipations be realised — if it 
be found that the malaria-bearing species of mos- 
quito multiply in only small isolated collections of 
water which can easily be dissipated — we shall possess 
a simple mode of eliminating malaria from certain 
localities. I limit this statement to certain localities 
poly, IjeQftUs? it is pbyipus that wherp the breeding 
