553 



evidently eager to get a feed of blood, but unable to do so so long as the 

 atmospheric temperature remained below 23° C. Nor have I ever, as far 

 as my records show, witnessed a successful bite by a mosquito of that 

 species, including the sucking of a fair quantity of blood, when the 

 atmospheric temperature was less than 24° C. 



From these data I have inferred that the lowest temperature-limit at 

 which, during the winter season, the Havana stegomyia can accomplish 

 such a bite as will enable it to become contaminated from a yellow fever 

 patient or to Ijay successive batches of ova for the propagation of its own 

 species, lies between 23° and 25° C, a condition of things which obtains 

 in Havana, at certain hours of the day, when the diurnal mean temperature 

 reaches 23° C. 



Regarding the hot temperature-limit beyond which the stegomyia 

 should be prevented, by excess of heat, from accomplishing a successful 

 bite, I do not believe that it ever occurs, in the shade, in this part of the 

 Island, for all hours of the day ; but it is possible that the occurrence of 

 such a limit in the vicinity of the equatorial line may have contributed to 

 retard the extension of the yellow fever infection, along the Atlantic coasts 

 of America, from the Northern to the Southern hemisphere. 



My surmise that during the winter season in Havana, a diurnal mean 

 temperature from 23° C. upwards should be considered as characteristic of 

 days when the local stegomyias are in a condition to become infected and 

 to transmit the yellow fever infection, received a practical confirmation 

 in the course of an investigation which I undertook in 1893. — As far back 

 as our yellow fever statistics reached at that time, and more particularly 

 regarding the 13 years' period from 1880 to 1892, only once could I find in 

 the records of the Belen Observatory an entire month without a single day 

 showing a diurnal mean temperature as high as 23° C. This happened in 

 the month of January 1886; and in the following month (February 1886) 

 there had been only two days, one with a mean temperature of 23° and 

 another of 24° C. — And coincidently with these exceptionally low mean 

 temperatures, I found, also as a unique exception in a long series of years, 

 that during the first five months of that year ( 1S86) only two cases with no 

 deaths had been recorded at the Havana Military Hospital, while in the 

 Civil population (where only the deaths were recorded) only eight deaths 

 had ocurred (4 in January, two in April and two in May) with the 

 circumstance that the 4 deaths in January had occurred in the first week 

 of that month so that the infection in these 4 must have been acquired in 

 the preceding month. Such a marked decline in the number of yellow fever 

 invasions was an unprecedented event in Havana, and was all the more 

 remarkable inasmuch as no measures had been taken to control the 

 propagation of the disease or to prevent its importation from outside In 

 fact it virtually amounted to an almost complete extinction of the infection 

 through purely natural causes. 



