238 The Philippine Journal of Science 1915 
is not so time-consuming as it appears, since, in experiment 
1, one of us “‘cleaned”’ both sides of a very much obstructed brook 
for a distance of nearly 1 kilometer in three hours with no 
help except that of assistants to carry a supply of crude oil. 
The brook was much obstructed by trees and jungle and was 
one of the worst in this respect of any we have visited in the 
Philippines. 
In order to control the results of the larvicide in our experi- 
ments, the whole distance to be treated was first surveyed. At 
certain stations dips were made at the margins with the collect- 
ing dish, the larve obtained were counted and replaced in the 
water, and the results were entered in a note book. The stations 
were marked, usually with numbered stakes made conspicuous 
with strips of red cloth. At a known interval of time after the 
application of the larvicide, dips were again made at the stations 
and at points between them, and the larve counted. The dips 
were made in places where by long experience in collecting we 
knew that larve were likely to be found. The streams in all 
experiments contained clear flowing water, and there were few 
larve other than of Anopheles febrifer present. There had been 
no preliminary clearing away of breeding places. In experi- 
ment 4 the water had been shut off from the ditch half an 
hour before the application of the kerosene, and was not turned 
on again for some hours. As a result, the quantity and the 
movement of the water were diminished, and the larvicide was 
made more effective. After the application of the larvicide the 
stream was searched for larve before the water was turned on, 
and was searched a second time some hours after the water had 
been allowed to flow into it. 
The percentage of larve destroyed can be estimated only 
approximately, but it is apparent from the data given in the 
table that from 95 to 100 per cent of the larve of Anopheles 
febrifer may be destroyed by one application of any good lar- 
vicide where it is well worked into the breeding places. Where 
the breeding places are limited to one or two small streams in 
or near a town; as is frequently the case in the Philippines, one 
trained person could keep down the larve for a distance of 
at least several hundred meters above and below the town. 
Our data also show that the time and expense required are 
not great. In our experiments we “scrubbed” the entire margins 
of both banks, except at certain points which were left as 
controls. If we had confined the treatment to known breeding 
places, much time and larvicide might have been saved. How- 
ever, where the larvicide is applied by a person unfamiliar with 
