PROPHYLAXIS OF MALARIA. 
61 
the banks of streams and of vegetation and algae in the streams or 
of any shelter for the mosquitoes, such as is furnished by jungle, 
long grass about residences, and vines and bushes, is a valuable pro¬ 
phylactic measure. The removal of the vines so often observed in¬ 
closing the porches of barracks and quarters in some of our most 
malarious posts should be insisted upon if mosquitoes can not be 
eradicated, as they furnish shelter to many of these insects, and their 
removal will result in a great diminution in the number of mosquitoes 
and, consequently, in the prevalence of malaria. The same is true 
of all shrubbery about habitations, and the measure adopted in the 
Canal Zone of removing all such vegetation for 200 yards around 
the houses could be followed with excellent results in more than one 
of our Army posts. 
The clearing of rank vegetation and jungle for several hundred 
yards around a camp or post is not only useful because it deprives 
the mosquito of shelter, but it also results in the discovery of the 
small breeding places of the mosquitoes which could not otherwise 
be seen. The anopheline mosquito does not require a lake to breed 
in but, as has already been stated, will breed in the smallest de- 
pressions in the ground that will hold water, and every clearing 
operation, especially in the tropics, always results in the discovery 
of many of these minute breeding places. 
At Camp Stotsenburg, in the Philippines, it was invariably noted 
that mosquitoes increased greatly in number whenever the grass 
about the post was allowed to grow to any great length and that 
a coincident increase occurred in the number of malarial cases ad¬ 
mitted to hospital. At one time, owing to lack of facilities for 
cutting, the grass was allowed to grow for several weeks, and the 
mosquitoes became so numerous as to be almost unbearable, while 
the number of cases of malaria admitted to the hospital became 
alarming. As soon as the grass was mowed the mosquitoes decreased 
in number, as did the number of malarial infections, thus conclu¬ 
sively proving the danger of affording shelter to the mosquito. 
Destruction of mosquito larvce with larvacides. —While, the drain¬ 
age or filling in of the larger bodies of water that are breeding places 
for mosquitoes is the ideal method of dealing with them, it fre¬ 
quently happens that this is impossible owing to various local con¬ 
ditions. When this is the case the larvae may be killed by certain 
substances which may be added to the water, and this furnishes us 
with a prophylactic method of considerable value. 
Many substances have been recommended for this purpose, the most 
important of which will now be considered: 
Petroleum .—The use of kerosene as a larvacide was first recom¬ 
mended by L. O. Howard, 28 and it has been used very largely by the 
