GAB, Barber et al.: Malaria in the Philippines 239 
the breeding places, it would be inadvisable to skip any part 
of the bank. 
A practical application of our method of larva destruction 
has been made by Dr. I. S. Diller, of the Calamba Sugar Estate. 
The brook treated by us in experiment 1 flows near a large barrio 
of the estate. This brook has been systematically treated op- 
posite and some distance below the barrio by an assistant whom 
we trained. Doctor Diller reports a diminution both in the 
number of mosquitoes and in the cases of malaria in the barrio. 
We have not observed much tendency in these larvz to follow 
the current down the stream, except when there is abundant 
floating débris for them to cling to. In experiment 4 the treated 
ditch was found practically free of larve nineteen days after 
the ditch had been opened to the main ditch above, where larve 
were plentiful. It is probable that if a portion of a stream is 
thoroughly cleared it will remain so until a fresh supply of 
larve have had time to develop. 
As stated above, we found that larvicide merely poured on 
the brook was comparatively ineffective. One experiment con- 
ducted on the same brook as that described in experiment 1, 
Table X, may be described in detail. Twelve dips at 12 stations 
gave, before treatment, 150 larve. The distance was approx- 
imately 100 meters. Then about 3 liters of crude oil were 
poured on the stream at the upper station. Twenty-four hours 
later the brook was again examined. Twelve dips at the sta- 
tions gave 36 larve, and 78 additional dips above and below 
the stations gave 95 larvee, a total of 131 larve. The average 
numbers obtained per dip were 12.5 larvee before treatment, 
1.5 larvee after treatment. The destruction of the larve was very 
marked where the current was comparatively slow and the 
margin of the bank little protected by vegetation, but it was 
very little where the current was swift and the bank protected 
by overhanging roots and ferns. In experiment 1, Table X, 
certain stations were left untreated as controls. These stations 
showed decidedly less diminution of the larve than did the 
places where the larvicide was worked in. 
In Magdalena, at the same time that experiment 4 was made, 
a ditch on another street was partially dammed, and a quantity 
of petroleum was placed immediately below the dam and at other 
points below. Then the water was liberated so that the larvi- 
cide could be carried down by the rush of the stream. There 
was some destruction of larve, but the results were not wholly 
satisfactory. A second experiment of the same sort also gave 
indifferent results. It seems that it is necessary to work the 
