i 7 9 
FACTORS IN THE TRANSMISSION 
AND PREVENTION OF MALARIA 
IN THE PANAMA CANAL ZONE 
BY 
S. T. DARLING, M.D. 
(Received for publication 7 June, 1910') 
INTRODUCTION 
In every malarial region it is important that the species of 
mosquitos common to that region should be lecognised, their 
breeding habits should be studied, and a determination made of 
the species of Anophelines, hospitable to malaria, and those 
transmitting it. The English observers, Stephens and Christophers, 
noticed that certain species of Anophelines were natural 
transmitters of malarial fever, while others were rarely, if ever, 
found infected naturally, although it was possible to infect 
them under laboratory conditions. We know that the breeding 
habits of Anophelines vary, too, considerably, and it may be said 
that there is as much selection of breeding places by Anophelines 
as there is selection of feeding grounds by fish. Trout, salmon, 
and bull-heads have their analogues among Anophelme larvae; 
some of the latter requiring fresh aerated water, or water containing 
much green algae. Others are found in tree-holes and recesses o 
epiphytic tree plants, such as Bromelias, whcic they prey upon 
other species, while others preferring fresh aerated water are so 
adaptable that they will flourish in sewage streams, or m brackis 
water containing half its volume of sea water. 
Some species require an abundance of sunlight, vdn c 
sylvan species prefer shady pools in which chlorophyll-bearing 
algae are relatively absent. 1 he Anophelines insuscepti 
malaria may be more limited in their choice of breeding p aces, 
that in the work of malarial mosquito destruction the latter may 
