Period of Great Epidemics


57


carried out as a basis for his M.D. thesis at the University of Pennsyl-
vania (I802-3) had been frequently overlooked. They were, however,
cited by La Roche (i 855) and by Carlos Finlay. In spite of this, how-
ever, fears of fomites from yellow fever cases were so deeply imbedded
that the commission felt it necessary to test this means of spread under
well-controlled conditions.
   Their efforts were first directed to determining the part that Bacillus
 icteroides of Sanarelli played in causing yellow fever; this organism
 because of some recent investigations by Wasdin and Geddings seemed
 to be implicated. However, careful blood cultures from 18 cases, i I
 severe with 4 deaths, 3 well marked, and 4 mild, were all negative for
 this organism, and cultures taken from the organs of i i cases at autopsy
 were also negative. Furthermore, Reed and his colleagues found that
 B. icteroides and the so-called hog cholera bacillus, B. cholerae suis,
were
 highly similar and that similar lesions could be produced in experi-
 mental animals by injecting cultures of either organism. So this bac-
 terium went the way of the others, merely a secondary invader or a
 contaminant.
   Carter (1898 et seq.) in Mississippi, with especially favorable condi-
tions for determining the interval between the arrival of infective cases
and the occurrence of secondary cases in the houses, had found that this
period was consistently between 2 and 3 weeks. With an incubation
period in man of 2 to 6 days, rarely a day shorter or longer, a lapse of
9 to i6 days for development in some intermediary host such as the
mosquito seemed not improbable. Others, notably Hosack (i 824) and
La Roche (1855) had made similar observations, but Carter was the
one whose voice became convincing. This possible extrinsic incubation
period, and the fact that the disease was not immediately contagious
tied in beautifully with Finlay's mosquito theory. These points, to-
gether with the failure of everyone in attempts to infect the common
laboratory animals and the several similarities between the epidemi-
ology of malaria and yellow fever, led Reed and his colleagues to make
the difficult decision to experiment with mosquitoes and human volun-
teers. Carlos Finlay immediately and with gracious enthusiasm placed
his papers, his findings, and his experience at their disposal. He pro-
vided them with eggs of his preferred species of mosquito; with these
the commission began their mosquito colony.
  General Leonard Wood, the military governor of Cuba, himself a
physician, gave encouragement, the necessary permission, adequate