236 



to be silent on the symptoms of the disease, and to attribute the numerous 

 deaths that had to be registered among the new-comers to change of 

 climate, to improper food, or to excessive heat. It is possible also that, at 

 that time, the disease may not have been commonly attended with what is 

 now, in fatal cases, its most striking symptom (black vomit), and death 

 may have been occasioned (as sometimes happens even now) by the 

 intensity of the primary infection, through nephritis and uraemia. Be this 

 as it may, however, it is in reference to the year 1648 that the first recog- 

 nizable descriptions of yellow fever epidemies are met with, in Dutretre's 

 Historie Genérales des Antilles, and in Corgulludo's Historia de Yucatan, 

 the former refering to Guadaloupe and the latter to the Peninsula of 

 Yucatan, both authors having been eye-witnesses of the events which they 

 describe. 



In Havana the disea.se had probably become a permanent endemic since 

 the beginning of the present century. Certainly during the last fourteen 

 years, and probably for a much longer period, not once has a whole month 

 elapsed without the occurrence of some case of yellow fever in this city. 

 The true epidemic season, however, — the period during which the disease 

 shows a decided tendency to spread, — is generally comprised between the 

 months of May and October ; the monthly mean temperatures, in the shade, 

 being then between 25° and 29° C. ; and the maximum between 35° and 

 39° 5 C. When the mean temperature, for a succession of weeks, falls to 

 20° C. (as occasionally happens between December and February), the 

 disease shows a tendency to die out. On certain years (generally those in 

 which the monthly mean temperatures rise above the average), not only 

 are the cases more numerous and the attacks more severe among the unac- 

 climated, but even persons who already considered themselves secure 

 against the infection may then occasionally be attacked. 



Nature of the Disease. — Yellow fever is most probably a germ disease. 

 Until a comparatively recent date, violent controversies were carried on 

 between equally competent and reliable observers regarding its contagious 

 or non-contagious character; but the best authorities on this side of the 

 Atlantic seem now agreed that, although yellow fever is not contracted 

 by direct contact with the patients, nor by inhaling the emanations from 

 the sick or the dead, nor by the use of contaminated food or drink, yet it is 

 unquestionably transmissible and specific, in so far that its occurrence 

 invariably implies the introduction of a specific cause derived from a 

 previous case of yellow fever. 



The negative conditions just mentioned are borne out by numerous 

 examples of susceptible persons who subject themselves to direct contact 

 with the patients, or inhale the emanations in the sick-room, without 

 thereby contracting the disease, and also by the fact that in colleges, 

 convents, barracks, etc., when several of the inmates become infected, they 

 are seldom attacked in such order as would lead one to suppose that they 



