453 



attack would result from a greater number of such stings and the same 

 might also occur in consequence of a single sting from a mosquito that 

 should have been fed exclusively on sweet juices during several days or 

 weeks, after its contamination, before it is allowed to sting another non 

 immune subject. In this case the germs have had time to develop more 

 abundantly, not having been wiped off during the interval, and the 

 virulence of the inoculation might be expected to become proportionately 

 increased. The climatic and topographical conditions that are known to 

 favor the propagation of yellow fever may be reduced to three: 

 temperature, between 70° & 90° F., atmospheric moisture with proximity 

 to the sea coast or water courses, and low levels above the sea-board never 

 exceeding 4,000 feet nor generally above a few hundred. The same 

 conditions seem likewise indispensable for the vitality, functional activity 

 and reproduction of the Culex Mosquito. Being a hibernating insect whose 

 functional activity is adapted only for tropical! climates it becomes 

 benumbed and unable to sting when the temperature falls below 65° or 

 60° and it may be kept at low temperatures in a state of apparent death, 

 from which however it revives when the temperature is raised to 65° or 

 70°, provided the refrigeration has not been carried below 32° F. 

 Moreover, the same limits below 70° or 65° appear to impede the 

 transformation of the larvae into the adult, winged insect. On the other 

 hand high temperatures beyond 95° F., also deprive the mosquito of its 

 movements and it dies at 105° or 110° F. It is a matter of observation that 

 mosquitoes abound most on damp summer days and the vicinity of water 

 is essential for the development of its aquatic larva?. The influence of 

 altitude I have only been able to test by an indirect method. When the 

 insect is confined in an atmosphere rarefied to a degree corresponding to 

 altitudes of 4,000 to 6,000 feet, it is unable to fly, and loses, for a while at 

 least, its functional powers. If we consider the smallness of its wings it 

 seems unlikely that the Culex Mosquito will, of its own accord, fly to any 

 considerable height or distance, and when weighted by the blood it has 

 ingurgitated it would hardly rise many feet above the floor in search of a 

 hiding place where it may safely digest its recent meal. These peculiarities 

 agree with what is known of the propagation of Yellow Fever, its tendency 

 to invade the lower stories of a building in preference to the upper ones 

 and the non transmissibility of the disease in places like the City of 

 Mexico, Orizaba. Petropolis situated at great altitudes above the sea. 



In my communications to the Havana Academy of Sciences in 1884 

 and 1885 I have collected abundant evidence to show that in many 

 instances, dating back from the earlitst epidemics of the peste which 

 decimated the Spanish invaders on their first arrival in the tropical 

 regions of America, to the modern accounts of yellow fever epidemics given 

 by Laroche and in Barton's Reports, the abundance of mosquitoes in the 

 localities where disease prevailed is particularly mentioned. In one instance 



