ividuals, having recently arrived in
Havana, were liable to attacks of yellow fever, or of "acclimation
fever" as a result of their residence in this city and quite
independently of Dr. Finlay's mosquito inoculations. For these reasons
Dr. Finlay's experiments failed to convince the medical profession
generally of the truth of his theory relating to the transmission of
yellow fever, and this important question remained in doubt and a
subject of controversy. One party regarded the disease as personally
contagious and supposed it to be communicated directly from the sick to
the well, as in the case of other contagious diseases, such as smallpox,
scarlet fever, etc. Opposed to this theory was the fact that in
innumerable instances nonimmune persons had been known to care for
yellow-fever patients as nurses, or physicians, without contracting the
disease; also the fact that the epidemic extension of the disease
depends upon external conditions relating to temperature, altitude,
rainfall, etc. It was a well-established fact that the disease is
arrested by cold weather and does not prevail in northern latitudes or
at considerable altitudes. But diseases which are directly transmitted
from man to man by personal contact have no such limitations. The
alternate theory took account of the above-mentioned facts and assumed
that the disease was indirectly transmitted from sick to well, as is the
case in typhoid fever and cholera, and that its germ was capable of
development external to the human body when conditions were favorable.
These conditions were believed to be a certain elevation of the
temperature, the presence of moisture and suitable; organic pabulum
(filth) for the development of the germ. The two first-mentioned
conditions were known to be essential, the third was a subject of
controversy.

Yellow fever epidemics do not occur in the winter months in the
temperate zone and they do not occur in arid regions. As epidemics have
frequently prevailed in seacoast cities known to be in an insanitary
condition, it has been generally assumed that the presence of
decomposing organic material is favorable for the development of an
epidemic and that, like typhoid fever and cholera, yellow fever is a
"filth disease." Opposed to this view, however, is the fact that
epidemics have frequently occurred in localities (e.g. at military
posts) where no local insanitary conditions were to be found. Moreover,
there are marked differences in