1915] Ecological Foundations of Applied Entomology 13 
There was, to begin with, a general background of knowl- 
edge, variously acquired, of the parasitic relationship—the 
relation of internal parasite and animal host—a purely ecolog- 
ical subject. Next in logical succession came the question of 
the paths and modes of transmission by which a parasite - 
passes from host to host—again an ecological inquiry, in the 
course of which it was found that some parasites require two 
kinds of hosts in alternation for the completion of their life 
histories, and that these two hosts are usually—almost neces- 
sarily, indeed—animals ecologically associated. In rational 
but not chronological order, then follow (2) the discovery of 
protozoan parasites, eventually including a blood parasite in 
man invariably associated with malarial disease, and a special 
study of the habits and development of this parasite in man; 
(3) prolonged but vain search for it outside the human body in 
situations where malarial disease was prevalent; (4) the sug- 
gestion of mosquitoes as possible carriers of the malarial poison, 
a hypothesis based on the coincident distribution of mosquitoes 
and malaria; (5) experimental tests of this hypothesis by the 
feeding of mosquitoes with blood from malarial patients, and 
search for the human-blood parasite in their bodies—experi- 
ments which were successful when the right species of mosquito 
were chosen; (6) studies of the life history of the parasite in the 
mosquito’s body; (7) successful experiments in the inoculation 
of man with malarial disease by means of mosquitoes containing 
the malarial.parasite; (8) field studies of the precise distribution 
and reproductive habits of Anopheles; (9) experiments with 
practical measures for the local control of malarial disease by 
an elimination of the breeding places of malarial mosquitoes; 
(10) the construction of a program of practical operation and 
requirement for the local abolition of malaria; (11) the passing 
of ordinances and the issuing of orders for the execution of this 
program; and finally (12) the organization and management of 
a competent executive force, with authority sufficient to carry 
such a program out effectively. Thus was accomplished 
the virtually perfect result in Panama; and by a duplication of 
these methods, so far as they were applicable to a disease whose 
germ has never yet been seen, yellow fever was also mastered. 
In all this series it is the /ast step which costs; the malarial 
parasite and the mosquito are less refractory to the control 
of man than man himself; it is less difficult to perfect methods for 
