64 
PROPHYLAXIS OF MALARIA. 
the use of kerosene is expensive and often inefficient. The cost of 
preparing it is stated by Darling to have been but $0.1413 per gallon, 
which is very much less than any fuel oil can be purchased for. and 
1 gallon of the larvacide makes 6 gallons of the preparation when 
diluted with water for use in the spray. In addition this larvacide 
is a good germicide, having a Rideal-Walker coefficient of from 2 
to 5. One, or at most two, larvacide plants could supply all the larva¬ 
cide needed in the Philippines, and the same is true of the United 
States, and the manufacture and use of this substance bv the Govern¬ 
ment would result in a considerable reduction in the cost of malaria 
prophylaxis and at the same time furnish the Army with a more 
efficient larvacide than kerosene oil. 
Other Icirvacides .—Among other substances that have been recom¬ 
mended as larvacides may be mentioned permanganate of potassium, 
sulphate of copper, corn oil, Phinotas oil, and many proprietary 
preparations. None of these are as efficient as the larvacides already 
mentioned, and the only one that has been used extensively is Phino¬ 
tas oil, which has been used to a considerable extent upon the Isthmus 
of Panama. It is capable of quickly killing the larvae, but also kills 
fish, so that it should not be used where it is desired to preserve the 
latter. 
Although it is possible to secure very excellent results in the 
prophylaxis of malaria by the use of larvacides the method is always 
an admission that we are unable to control mosquito breeding by the 
much better one of abolishing the breeding places of these insects, 
and it should never be adopted in preference to the latter. Under 
the best conditions it is imperfect and the results are not to be com¬ 
pared with those obtained by drainage or filling in of breeding places. 
In addition, especially in the Tropics, the method is more expensive, 
because the results are not permanent, the use of the oil having to 
be continued for months, while, even in temperate regions, it is 
doubtful if this method is as economical as the abolition of the 
breeding places. It finds its greatest field of usefulness in those 
instances where breeding places can not be abolished owing to the 
expense involved, or where open ditches and streams can not other¬ 
wise be prevented from becoming breeding places of these insects. 
Destruction of larvce by fish .—The well-known fact that several 
species of fish are voracious devourers of mosquito larva? has been 
taken advantage of in the prophylaxis of malaria, and there are 
many accounts in the literature of attempts to render the breeding 
places of mosquitos harmless by the introduction of fish that will 
devour the larvae. There is no question that in many instances these 
attempts have met with a considerable amount of success but, as a 
rule, the results have been disappointing. The fish that are the most 
useful are the roach, carp, top minnows, and the goldfish, the roach 
