7 i8 THE POPULAR SCIENCE MONTHLY. 



rarely occurs inland, but follows water-courses and lines of ocean-travel, 

 and so usually appears in commercial cities, and begins its march at 

 the wharves. It is uncommon in elevated regions, and 2,500 feet is 

 commonly regarded as its altitudinal limit, but it has been known to 

 occur at Newcastle, Jamaica, at a height of 4,000 feet, and if the belief 

 be true that ancient Mexico was visited by it under the name of matla- 

 zahuatl, then it has been epidemic at a height of between 7,000 and 

 8,000 feet above the sea. 



There has been no severe epidemic of this disease in New York 

 since 1822, but it breaks out on our Gulf and South Atlantic coasts at 

 intervals, with no appearance of periodicity. It first appeared in New 

 Orleans in 1796, and has often been epidemic there since. The most 

 fatal epidemic was that of 1853, when the deaths were variously stated 

 at from 8,000 to 10,000, or about eight times as many as have occurred 

 there during the present summer, though the population was only half 

 as large. It is the common impression that New Orleans was saved 

 from the disease during its occupation by Federal troops in 1862-'65, 

 because the city was put in such excellent sanitary condition ; but Dr. 

 Nott calls attention to the fact that there are often periods of exemp- 

 tion from the disease in all places visited by it, and that in New Or- 

 leans in 1859 there were only 91 deaths from yellow fever, in I860 

 only fifteen, and in 1861 not a single one ; while in 1863 Dr. Harris 

 says there were nearly 100 cases of the disease, with two officially 

 recorded deaths, and in 1864 more than 200, with 57 deaths. 



Yellow fever occupies a singular position between the contagious 

 and non-contagious diseases. The poison is not, like that of small-pox, 

 directly communicable from a sick person to a well one ; but, although 

 the emanations of the sick are connected with the spread of the dis- 

 ease, they seem to require an appropriate nidus in which to germinate 

 and develop. This nidus must be warm and moist, and there the 

 germs, whatever they are, lie and grow, or, in some way develop until 

 they are able to migrate. The germs are portable, and may be con- 

 veyed in baggage or merchandise (fomites) for hundreds or thousands 

 of miles. If not so conveyed, its progress is very slow. In 1822 in 

 New York, when it gained a foothold in Rector Street, it appeared to 

 travel about forty feet a day until killed by the frost. It often leaves 

 a house or a block intact, going around it and attacking those beyond, 

 with no assignable reason. A thin board partition seems to have 

 stopped it on Governor's Island in 1856, and an instance is related 

 where it attacked the sailors in all the berths on one side of a ship 

 before crossing to the other. Such apparent vagaries are, in the pres- 

 ent state of our knowledge, inexplicable. 



