188 Proceedings of the Royal Society of Edinburgh. [Sess. 
influx of non-immune strangers during the war resulted in an outbreak 
of yellow fever. In 1900 an American Army Commission was sent out 
to study the disease, of which Dr Walter Reed was the best-known 
member. Taking their cue from Ross, who four years before had proved 
that malaria was transmitted from man to man by the bites of Anopheles 
mosquitoes, themselves infected by sucking the blood of malaria-stricken 
men, Dr Reed and his assistants turned their attention to the local 
mosquitoes, which had already, in 1881, been suspected by Dr Charles 
Finlay of being the cause of spread of yellow fever in Havana. By 
experiments on themselves they proved that yellow fever was due to 
the bites of a species of mosquito, Stegomyia fasciata, and not to contact 
with the patient, his clothes, or fomites. They found that the Stegomyia 
lives for three months. It becomes dangerous only by imbibing the blood 
of man during the first three days of an attack of yellow fever, and even 
then twelve days elapse before its bite is infectious ; six days after a person 
has been bitten by an infectious Stegomyia he develops yellow fever, and 
for the next three days his blood is capable of infecting a Stegomyia. In 
no other way can yellow fever be spread. The Stegomyia breeds chiefly 
in or near towns, being a domestic mosquito, in contradistinction to the 
ljialaria-carrying Anopheles, which loves clean water and jungle streams. 
The Stegomyia breeds on the surface of cisterns, stagnant pools, or in old 
pots in neglected backyards. 
This discovery was at once seized on by Gorgas, who was Chief Sanitary 
Officer of Havana. Fortunately the Governor was General Wood, who 
had studied medicine for several years, and he gave Gorgas a free hand, 
and he at once turned the whole energies of the organised sanitary 
department to rid Havana of the infected Stegomyia. The patients were 
screened in hospitals, so that mosquitoes could not get at them. All 
breeding-places, such as cisterns, were screened, tubs and tanks, old pots, 
etc., were emptied, and severe fines were imposed on persons with open 
water on their premises. The methods were described by Gorgas’ 
opponents as ruthless, but in a few months Havana was free of yellow 
fever. It remained free for three years. “ The government was then 
turned over to the Cubans,” and yellow fever reappeared. In 1906 the 
United States again assumed control, the same sanitary methods were 
reapplied, and yellow fever again disappeared. 
For this triumph of applied science Gorgas was promoted to be Colonel 
and Assistant Surgeon-General by a special act of Congress. 
When the United States took possession of the Panama Canal Zone in 
1904 the great problem was, How can the health of the thousands of 
