PROPHYLAXIS OP MALARIA. 
59 
The malaria mosquitoes may be destroyed at any stage in their de¬ 
velopment, but most of the prophylactic methods depend for success 
upon the destruction of the insect during the larval and adult stage, 
the larvae being destroyed by the abolition of the collections of water 
in which they have developed or by larvacides, and the adult insects 
by various chemical agents or other measures. The most important 
measures consist in the abolition of the breeding places of the mos¬ 
quitoes by leveling, drainage, and clearing, and if they can be carried 
out in an efficient manner they are the most valuable that we possess, 
and in the vast majority of instances are capable of geatlv reducing, 
if not almost eradicating, malarial disease. Unfortunately, the ter¬ 
rain often renders the application of these measures very expensive 
and other prophylactic methods are substituted, but, where it is pos¬ 
sible, I believe that these measures, although the first cost may be 
great, should be the ones adopted, as they produce permanent results 
and in the case of many of our Army posts would banish malaria 
from the sick report. 
Drainage .—If possible all large breeding places of mosquitoes 
should be drained, if they can not be filled in or otherwise abolished. 
If filling in is feasible, this is the better method, but the relative cost 
of the two methods must be considered for each localitv and the 
choice made as to which will be the cheaper and most efficient. 
If drainage is decided upon, the question arises as to the particular 
kind of drainage to be used. In many temperate and subtropical re¬ 
gions open ditches may be used, provided the edges are kept free from 
plants and algae and there be enough slope to give a compara¬ 
tively swift current. Otherwise, the open ditch, although it may 
drain a larger body of water, simply becomes a mosquito breedery, 
and this is almost sure to happen in the Tropics, where it is practically 
impossible to prevent the growth of plants and algae in the water of 
the ditch. This fact has been well brought out by Le Prince 26 , who 
says: 
On the Isthmus and probably throughout the Tropics, under average conditions, 
we could not consider such a mode of procedure (the open drainage ditch) as 
it would give most unsatisfactory results. Such a ditch would become a ver¬ 
itable Mecca for anopheles. 
In order to prevent the development of vegetation in the ditch it 
would have to be cleaned out in the Tropics on an average of once 
a week, and this alone would make their use practically impossible, 
as the cost of labor and upkeep would be too great unless the ditches 
were few in number and of limited extent. 
The blind drain .—Le Prince, 27 the chief sanitary inspector of the 
Isthmian Commission in 1008, recommends this method of drainage 
in case tile drains can not be obtained. He defines a blind drain 
u as a miniature culvert covered with field stones,” and states that 
