in yellow fever, is less than five days; and, third, because these individuals, 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 regard to the transmission of the recognized filth diseases—­typhoid fever and cholera—­and yellow fever.  The first-mentioned diseases are largely propagated by means of a contaminated water supply, whereas there is no evidence that yellow fever is ever communicated in this way.  Typhoid fever and cholera prevail in all parts of the world and may prevail at any season of the year, although cholera, as a rule, is a disease of the summer months.  On the other hand, yellow fever has a very restricted area of prevalence and is essentially a disease of seaboard cities and of warm climates.  Evidently neither of the theories referred to accounts for all of the observed facts with reference to the endemic prevalence and epidemic extension of the disease under consideration.