15 
insects, fresh supplies of which were constantly obtained by us 
from Wilberforce, where they were now to be found in greater 
numbers. Malaria parasites, in various stages, were detected in 
a fair proportion of those examined. In some specimens the 
salivary glands and ducts were found packed with zygotozoids — 
the young form of the parasite which is destined to pass into the 
blood of a human being when the mosquito takes its next meal. 
That a small quantity of kerosene poured on to the surface of Experiments 
the water would kill mosquito larvae was well known before the ^Anophlj?."^ 
visit of our expedition to Freetown. The oil forms a film on larvae by 
i „ t • i i i -ii 11 means of 
the suriace, which the larva? are unable to penetrate when they kerosene. 
come up to breathe ; they are thus speedily suffocated, especially 
since the oil gets into and blocks their respiratory apertures 
Major Koss found that a very young Anopheles larva in a watch- 
glass full of water with a trace of kerosene on the surface died in 
ten minutes, and that a half -grown larva under similar conditions 
perished in half an hour. Other substances (such as tar and 
creosote) have similar properties, and an extensive series of 
comparative experiments upon this subject have recently been 
made in Italy. Kerosene, however, was selected by us as being 
cheap, convenient to use, and readily obtainable. 
On September 7th an experiment in destroying Anopheles larvae 
in a puddle by means of kerosene was performed in the presence 
of Drs. Prout and Berkeley, and was completely successful. 
The oil was applied in the morning, and most of the larva? wer e 
apparently dead at the end of half an hour; the puddle was 
again visited about 5.0 p.m., when there was no doubt that not a 
single larva remained alive. On this occasion a small quantity 
of oil was poured on to the water from a bottle. It did not, 
however, spread over the surface as quickly and completely as 
was expected, and it was found necessary to stir the water with a 
stick before a film covering every portion of the surface was 
produced. It was subsequently discovered that a rag tied to the 
end of a stick affords the best means of applying the oil to puddles. 
Our next task was to prepare a map, showing the situation Mapping-oat 
of the breeding-places of Anopheles in Freetown. For this pjj^g ^ 
purpose, a street-plan of Freetown having been obtained, each -I HopheU* 
street was carefully examined anew, and the position of every 
