of the disease outside of the West Indies, for the reason that, in the comparatively few places where it is now endemic, there is historical evidence to show that there was a first im portation and a previous period of exemption; while, on the other hand, the conditions upon which endemicity at the present day seem mainly to depend, were formerly unknown— conditions arising from the aggregation of pop ulation at seaport cities, as at Havana, Vera Cruz and Rio de Janeiro.
In 1879 the writer went to Havana, as a member of a commission appointed by the Na tional Board of Health, for the investigation of questions relating to the etiology of yellow fever. One of the main objects in the appoint ment of this commission was the discovery, if possible, of the specific cause of the disease. The commission was fully equipped with the best microscopical apparatus, and with what ever else seemed necessary to promote the ac complishment of the object in view.
As a result of investigations made at that time and subsequently at Rio de Janeiro in 1887 and in Havana in 1888 and 1889, the writer formulated the following conclusions in a final report : "The specific cause of yellow fever has not yet been demonstrated.
"It is demonstrated that micro-organisms capable of development in the culture-media usually employed by bacteriologists, are only found in the blood and tissues of yellow fever cadavers in exceptional cases, when culture are made very soon after death.* Subsequent researches by other investiga tors have not invalidated these conclusions. For while the researches of Reed and his asso ciates have demonstrated the fact that the speci fic infectious agent ("germ") of the disease is present in the blood, they have failed, as here tofore stated, to isolate or to recognize this specific infectious agent, and no one else, up to the present time, has been more fortunate. Numerous claims have, however, been made to the discovery of the yellow fever germ.
A claim to the discovery of the yellow fever germ was made by Sanarelli, an Italian bacteriologist, who visited Brazil for the pur pose of making investigation with refer ence to the etiology of this disease. Sanarelli obtained from the blood of a certain proportion of the cases which came under his observation (post mortem) a bacillus which he believed to be the cause of the disease. His standing as a bacteriologist and his published papers relating the details of his experiments led to a general acceptance of his claims by members of the medical profession in Brazil and to some ex tent in other countries. But the researches of
Major Reed and his associates have shown that the Bacillus icteroides of Sanarelli is a com mon and widely distributed species which has nothing to do with the etiology of yellow fever, athough it may occasionally be obtained in cul tures from yellow fever cadavers. It was not present in any instance in the blood obtained from patients in the early stage of the disease, when this blood was proved by experimental in oculations to be capable of reproducing the disease in non-immune individuals, nor could it be obtained from the bodies of infected mosquitoes which has been proved to be cap able of communicating the disease.
Yellow fever is a disease in which immu nity results from suffering one attack, and this immunity usually lasts for many years, or for life. Second attacks may, however, occur, al though this is rare.
The mortality from the disease differs greatly in different epidemics and among differ ent classes and races. It has been asserted that the negro race has a congenital immunity from yellow fever, but this is a mistake. The sus ceptibility of the negro is, however, much less than that of the white race, and among those attacked the mortality, as a rule, is small. This is shown by the statistics relating to white and black troops in the British service at West India stations. "While in Jamaica the annual loss 'among the former amounts to 102 per 1,000 of the mean strength, the deaths among the blacks did not exceed 8 per 1,000. In the Bahamas the mortality of the whites was 59 in 1,000, that of the blacks 5.6 in 1,000* (La Roche).
In the report of the board of experts ap pointed by Congress to investigate the epidemic of 1878, we find the following remarks: "Ber wick City, 40 cases among colored, no deaths." "Morgan City, 21 deaths among colored per sons." "Brownsville (Tenn.), of 162 colored cases, 21 died." "Chattanooga, of 685 cases, 256 whites, 429 colored; of 164 deaths, 118 whites, 46 colored.* "Decatur (Ala.), of 64 white cases, 28 died; of 168 colored, 21 died." Barton gives the following figures, show ing the mortality per 1,000 among different races, and those of the same race from different latitudes, in the city of New Orleans in the great epidemic of 1853.