226 Annals Entomological Society of America [Vol. VIII, 
must let mosquitos enter until he quits talking. The finding 
of a greater number of Anophelenes in negro camps is explained 
by this fact. At Mira Flores the writer found that a negro 
camp with two doors had almost twice as many mosquitos as 
did a similar camp with but one door, not-with-standing that 
the camp with two doors was farthest away from the breeding 
place. 
The time of activity of the men is largely during the day- 
time, though sometimes forces have worked at night time as 
well. Men begin to emerge from their barracks as the first 
rays of the sun greet the new day, and they remain active until 
the last ray has departed. Mosquito activity is most pro- 
nounced during day-break and dusk. This coincidence bears 
a direct relation to the malarial rate. 
THE ENVIRONMENT. 
A. ITS COMPOSITION. 
In nature the composition and dynamics of the environ- 
ment are inseparable, but for convenience in the presentation 
of the subject, this division is necessary. 
I. Physical Factors. 
A. The Wind. For much of the meteorlogical data the 
writer is indebted to Mr. Wilson and his staff of the Weather 
Bureau of the Isthmian Canal Commission. 
During the months of January, February and March, 1913, 
the prevailing winds at Gatun were from the north. A sum- 
mary of the wind movement for January and March is given 
in table ““A’”’. Of the 744 hourly periods in January, 495 
showed north winds, and 164 showed northwest winds—a per- 
centage of 66.5 and 22.2 respectively of the total. Many 
winds reported as ‘‘west’’ or “‘northeast’’ were such by the 
mere addition of a dot or two on the record made by the auto- 
matic wind gauge. There were more westerly winds than 
northeasterly. In the month of March, northeast winds were 
wholly absent. In other words, the winds are predominantly 
from the north and northwest. This general prevalence in 
direction holds true for the entire year in the Atlantic section. 
