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visit with impunity a Yellow Fever patient, spending hours in his com- 

 pany, though on another occasion the same person may take the infection 

 when least expected. Others again appear to contract the disease in places 

 which do not lie within any presumable infectious area, hut where pack- 

 ages, bundles of clothes, etc., from an infected dwelling have been received, 

 or in which traffic or communication has been carried on with a centre 

 of infection at a greater or a lesser distance. This development of a se- 

 condary centre, far from a ease of Yellow Fever, must be considered excep- 

 tional in Havana, as compared with the more direct sources of conta- 

 mination. 



According to the susceptibility of each individual and the amount of 

 exposure, the intensity of the pathogenic consequences that will follow 

 may vary from the mildest disturbance which eludes the grasp of clinical 

 diagnosis, to the severest forms which, once seen, cannot fail to be recog- 

 nized even by a casual observer. In the milder forms, and even in severe 

 ones (when the symptoms are anomalous) it may be difficult to distin- 

 guish the disease from others that are common to most countries, unless 

 particular attention has been drawn to such distinctions. 



I cannot but believe that even the mildest degree of infection, when it 

 has once penetrated the system of a susceptible subject, will afford some 

 amount of immunity, though it may sometimes prove inadequate to shield 

 him against a future infection of much greater intensity. Permanent im- 

 munity, however, often results after a single or multiple infections of a 

 mild character, such as are seen in foreigners who only experience, during 

 the first three of four years of their residence, one, two or more attacks of 

 ephemeral or non-albuminuric fever, but who, after that period, can face 

 witli impunity the severest exposures. It seems probable also that both in 

 foreigners and in natives who have never presented any recognizable 

 attack of Yellow Fever, the immunity is maintained indefinitely through 

 occasional latent infections exempt of any pathological manifestations, for 

 they are apt to lose their immunity if they absent themselves during seve- 

 ral years from all Yellow Fever countries. The immunity which is enjoyed, 

 as a general rule, by native adults who have always lived in Havana has 

 been attributed to mild attacks suffered during early childhood, but which 

 liad not been recognized as such. I have recently obtained positive proof that 

 infants born within a short distance from this city may be attacked with 

 simple albuminuric Yellow Fever. A child, ten months old, and who had 

 always lived at Marianao, near the railroad terminus, only 12 miles dis- 

 tant from Havana, was attacked with fever presenting the typical Yellow 

 Fever curve, and with albumin in the urine from the 3rd to the 13th 

 day. Now in this case, had not the urine been examined there is little doubt 

 but that teething or malaria would have been made responsible for all the 

 symptoms. 



In rare instances, children have been born in the midst of epidemics, 



