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not so some are more likely than others to be mildly attacked, or to recover 

 when the attack happens to be severe. Thus the Chinese coolies and the 

 African negroes imported to the West Indies have, as a rule, proved refrac- 

 tory, extremely rare exceptions having been registered in Havana. After 

 prolonged residence in a temperate climate, through successive generations, 

 the Negro race loses to some extent its original! immunity, as has 

 been shown this very year during the epidemic at Brunswick (Ga.), in the 

 United States, several hundreds having there been attacked with yellow- 

 fever, though with a very low death-rate. A case has also been observed 

 in Havana this year in a Negro from the United States belonging to the 

 crew of an American vessel. Among the whites it is generally admitted 

 that, caeteris paribus, foreigners from northern climates suffer more seve- 

 rely than those from countries nearer the tropics. Within the tropical zone, 

 the inhabitants of highlands beyond 1000 feet above sea-level are susceptible 

 to the disease. The inhabitants of the island of Cuba who reside at some 

 distance from an endemic focus, even in low levels, and have had very 

 little intercourse with infected localities, are apt, on visiting centres of 

 infection, to suffer "acclimation fevers", and during severe epidemics 

 even albuminuric and melano-albuminuric yellow fever. If a ease declares 

 itself in such localities, an epidemic may be developed. In the neighbour- 

 hood of an endemic focus in the outskirts of Havana, and even in some 

 establishments within its precints (cloisterd convents), susceptible foreigners 

 may sometimes reside during a number of years without becoming 

 immune. 



Foreign children arc often attacked in Havana, but the disease is 

 generally less severe in them; it is also less fatal in youths under the age 

 of puberty, in women whose menstrual functions are regular, and in the 

 aged, than in young and middle-aged adults of the male sex. 



During an epidemic a complete or partial immunity is observed in 

 four classes of individuals of the white race who have presumably been 

 exposed to the infection, viz: 



1. — A small number among the newly-arrived foreigners, who, for 

 various reasons unknown, remain refractory to the disease, and continue 

 so in subsequent epidemics. 



2. — With very few exceptions, all those who have previously experien- 

 ced an attack of regular yellow fever, with well-marked albuminuria, either 

 recently or at some remotter period. 



3. — All the adults, and almost all the children who have been born and 

 bred in the city of Havana, never having absented themselves during 

 consecutive summers from the endemic focus. 



4. — The generality of foreigners who have resided during five or six 

 consecutive years in this city without having experienced the disease in 

 any form whatsoever, or only having had "acclimation fevers", the security 

 being greater in proportion as the time of residence has been longer. 



