od of incubation fall sick with the disease; being
bitten by other mosquitoes they serve to transmit the disease through
the "intermediate host" to still others. Thus the epidemic extends, at
first slowly from house to house, then more rapidly, as by geometrical
progression.

It will be seen that the essential difference between the successful
experiments of the board of which Dr. Reed is president and the
unsuccessful experiments of Finlay consists of the length of time during
which the mosquitoes were kept after filling themselves with blood from
a yellow fever patient. In Finlay's experiments the interval was usually
short,--from two to five or six days,--and it will be noted that in the
experiments of Reed and his associates the result was invariably
negative when the insect had been kept less than eight days (7 cases).

Having obtained what they considered satisfactory evidence that yellow
fever is transmitted by mosquitoes, Dr. Reed and his associates
proceeded to extend their experiments for the purpose of establishing
the fact in such a positive manner that the medical profession and the
scientific world generally might be convinced of the reliability of the
experimental evidence upon which their conclusions were based. These
conclusions, which have been fully justified by their subsequent
experiments, were stated in their "Preliminary Note" as follows:

1. Bacillus icteroides (Sanarelli) stands in no causative relation
to yellow fever, but, when present, should be considered as a
secondary invader in this disease.

2. The mosquito serves as the intermediate host for the parasite of
yellow fever.

In "An Additional Note" read at the Pan-American Medical Congress held
in Havana, Cuba, February 4,-7, 1901, a report is made of the further
experiments made up to that date. In order that the absolute scientific
value of these experiments may be fully appreciated I shall quote quite
freely from this report with reference to the methods adopted for the
purpose of excluding all sources of infection other than the mosquito
inoculation:

In order to exercise perfect control over the movements of those
individuals who were to be subjected to experimentation, and to avoid
any other possible source of infection, a location was selected in an
open and uncultivated field, about one mile from the town of Quemados,
Cuba. Here an experimental sanitary station was established under the
complete control o