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again to fill itself completely. This is the inoculation ; and when successful, 

 at the end of from five to twenty-two days incubation, the first symptoms 

 of mild yellow fever will manifest themselves in the inoculated subject. 



The process, as above described, is simple enough, but it must be 

 observed that in order to obtain available results several conditions are 

 necessary. A case of yellow fever must be at hand at the period most 

 favorable for the transplantation of the virus, which, according to my 

 experiments, seems to be from the third to the sixth day. A liable subject 

 must lie found willing to submit to the process, supposed to be free from 

 previous infection, and likewise willing to keep clear from infected places 

 during the incubation, yet within easy reach of observation. 



The nocturnal species of mosquito can easily be procured, but as before 

 stated, I have never succeeded in making that particular kind sting more 

 than once; whereas, the diurnal, which is the only one that I have 

 experimented with, does not generally come in swarms, but singly, or in 

 small numbers, making but little noise, and its bite is usually unfelt, at 

 least by the acclimated. 



These requisites, so difficult to be obtained by one whose leisure hours. 

 in the midst of an active professional life, are necessarily limited, will 

 account for the small number of my experiments, some twenty-four 

 individuals only having been inoculated by me since June, 1881. Of this 

 number only one has died of yellow fever; he had been inoculated in 

 November, 1883, without any visible result, and was attacked, after severe 

 exposure, in June, 1884, with a malignant form of yellow fever (it is the 

 second case of the series referred to elsewhere as instances of contagion). 

 Of the remaining twenty-three, two left the country, or were lost sight of 

 the first summer after inoculation; the rest having remained under obser- 

 vation during periods ranging between one and four full summers in the 

 city of Havana. Six of these inoculations were followed, within the 

 ordinary limits of yellow fever incubation (five to twenty- two days), by 

 an attack of fever, the exact counterpart of mild attacks of yellow fever, of 

 which I have kept careful notes, and which were proved by subsequent 

 observation to have conferred immunity. Eleven inoculations, though not 

 followed by any morbid manifestations within the limits of incubation, or, 

 at most (in three eases), by a trifling ephemeral fever, appear to have 

 likewise conferred immunity, in so far that the persons have resided in 

 the city of Havana, in constant exposure to the infection, during periods 

 of one or two summers, without experiencing any attack of the disease. 

 Finally, in four instances, not followed by any immediate morbid mani- 

 festation, at the end of several months a mild attack of yellow fever 

 (without albuminuria) was observed. 



These figures are not considered, from a statistical point of view, to 

 afford any definite clew either in favor of or against the prophylactic 



