Oct. 1, 1901. J THE TROPICAL AGEICULTURIST. 
2H9 
or if one is never stung by gnats one cannot 
get malaria : and if either the gnats or the 
malaria parasites are exterminated malaria must 
vanish for ever, because one of the factors 
absolutely necessary for its production has 
ceased to exist. How these proposals will stand 
the test of practice however, whether it is 
possible to carry them out to so general an 
extent as we had to suppose in estimating 
their theoretical value, is quite anoMier question. 
The discussion of this question is of special inter- 
est at present, because experiments are now being 
made everywhere with a view to provingthe practi- 
cability of the measures I have mentioned. I believe, 
therefore, that 1 may count on your assent, if I 
choose the said measures for the theme of this 
lecture, and take the liberty to discuss the measure 
proposed by myself in somewhat fuller detail. 
THE DKYING-UP OF SWAMPS. 
" If we begin with the drying-up of swamps, a 
measure which has been known from of old, we 
must regard its efficacy as confirmed by manifold 
experience and consequently as proved. Now, 
indeed, we know that the effect is not due, as was 
formerly supposed, to the prevention of the rotting 
of vegetable matter which was supposed to emit 
the gases that caused the disease, but to the des- 
truction of the breeding-places for the gnats. So, 
strictly speaking, this measure coincides with that 
aimed directly against the larvje of the gnats, of 
which I shall speak later on. Formerly attention 
was paid almost exclusively to extensive swamps, 
which could be dried up by regulating rivers and 
by means of deep drains through which the water 
could flow off. In this way districts have not 
infrequently been freed of malaria. In those 
cases, however, the purpose was always gained by 
very expensive works, of which it cannot even 
always be said that they were necessary, for it has 
been discovered that the anopheles gnats, which 
are the chief transmitters of malaria, have their 
breeding-places much more frequently in little 
puddles and pools than in great swamps. Several 
times in New Guinea I saw many larvse of anophe- 
les gnats in quite small gatherings of water, in 
wheel-marks and even in water-butts. In Italy 
I repeatedly found them in water- vessels which 
were placed in gardens for the purpose of watering 
the plants. In future, then, it will be necessary 
to pay attention to the small and even smallest 
gatherings of water— which can generally be 
rendered harmless by filling up or by frequent 
emptying — rather than to large swamp which 
cannot, as a rule, be easily got rid of. * * * 
LARVICIDE. 
"Of the direct extermination of the larvse of 
the gnats by destroying the breeding-places, 
pouring petroleum into the water, or other 
larvicidai means the same may be said. * *• * 
SEGREGATION. 
"The proposal to run away from malaria, so to 
speak, by living at least one mile away from all 
native settlements where malaria prevails, is one 
with which I have very little sympathy. * * * 
NETS, VEILS AND GLOVES. 
" The proposal to protect the inhabitants of 
malarial districts at night against the gnats' stings 
by nets, veils, and gloves sounds very plausible 
at first. It has been received with great enthu- 
siasm, and has been acted upon in Italy at many 
placesi and, to all appearance, with good success. 
But in the case of this measure, too, reasonable 
as it looks from the theoretical point of view, it 
was soon found that it admits of but very limited 
application in practice. In Italy at least the 
arrangements for securing houses against malaria 
seem not to have been resorted to yet, except in 
the case of the railway signalmen's cottages and 
some small railway stations; and as to the wearing 
of veils and gloves, it may peihaps be practicable 
in the Italian climate, but in the tropics the 
number of people that will willir.gly adopt this 
measure is not likely to he great. 
QUININISING THE POPULATION. 
" I come now to the measure proposed by my- 
self, which aims at exterminating the malaria 
parasites in man by means of quinine. In makin" 
this proposal I presuppose two things, firstly^ 
that the malaria parasites are restricted to man, 
and secondly, that we can destroy them, or at 
least render them harmless, by means of quinine. 
As to the first of these two presuppositions, I 
regard it as adequately proved by the fact that 
nobody has yet succeeded in finding parasites 
identical with the human malaria parasite in the 
blood of any animal. Ju-st as little has anyone 
succeeded in artificially transmitting human 
malaria parasites to animals. The second pre- 
supposition is proved by the observation that may 
be made in medical practice every day that, when 
quinine is properly used, the malaria parasites dis- 
appear from the blood of the patient. The fact, 
it is true, does not aftbrd certainty that they 
really are destroyed ; they may have only dis- 
appeared from the circulating blood, but renrained 
in the internal organs, especially in the spleen 
and in the bone-nrarrow. And in fact this is mostly 
the case after a single treatment with quinine, as 
the extreme frequency of relapses proves ; the 
malaria parasites are not got rid of till after the 
treatment with quinine has been continued for a 
length of time. 
"But as soon as one knows this effect o 
quinine on malaria parasites, one will of course 
not restrict one self to a single application of qui- 
nine, but will continue to give it in suitable doses 
till the parasites have really died. * * 
MICROSCOPIC EXAMINATION. 
" If, therefore, we wish to render all, or as nearly 
as possible all, parasites innocuous by quinine, w^ 
must take chronic sufferers from malaria and alsO 
the children into account. But the only way to 
gain this end is to examine the blood of all person^ 
suspected of malaria with the microscope. In all 
the attempts I have hitherto made to exterminate 
the malaria parasites I have acted on this principle, 
and have been able to convince myself that the 
execution of this measure is not o difficult as it 
may at first sight appear. * * 
MOSQUITOES' PREDILECTIONS. 
" A very interesting and also practically 
important fact strikingly observable at Pa- 
sana and partly at Stignano, too; th» ma» 
lariacases were specially numerous in ^ertain 
houses and groups of houses, and these were 
in the periphery of the place, whereas the centre 
was almost free. I had occasion to make the same 
observation before at the town of Grosseto in 
Italy. From this we may conclude that th» 
infecting inosquitoss do not fly anywhere and 
everywhere, or disperse equally over a place but 
have predilections for certain Now, |q 
