264 MOSQUITOES OF NORTH AMERICA 



between eight and eleven o'clock at night, in a room in his house or in his office 

 at the Museum at Para, with electric light, the windows open, he caught mosqui- 

 toes that settled upon his hands, biting him. Generally those which came at these 

 hours, certainly those from outside through the windows, were other species, 

 but from time to time, each time causing him a certain surprise, there appeared 

 also a female of calopus. In Eio de Janeiro he also noticed nocturnal bites by 

 this species, in a library on the lower floor of a house illuminated by gas, at about 

 the same hours. He noted that the room was papered with dark paper, and he 

 had always noticed that during the day he wa-s more persecuted by calopus in 

 that room than in any other. He soon learned that the deep moldings of the 

 furniture were the chosen hiding places for a large number of calopus. He also 

 ascertained that females in captivity could easily be induced to bite at night. 

 He asserts, however, that the yellow-fever mosquito is a diurnal species, but 

 admits that it may happen that hunger drives some females, who during the day 

 have not succeeded in obtaining their meal of blood, to prolong their hunt to 

 unusual hours, especially when guided by a bright light in the room. Biting at 

 night is therefore an exception, and they bite only in the presence of artificial 

 light. 



The French commission ( Annales de I'lnstitut Pasteur, vol. 17, 1903, p. 691) 

 assert that Aedes calopus is essentially a nocturnal mosquito. According to 

 their deductions calopus will only bite in the daytime within the first few days 

 after leaving the pupa, and then only when driven by hunger. They maintain 

 that when the female has reached a certain age, at the most two weeks, it will 

 under no circumstances bite in the daytime. They say that the belief of other 

 authors, that this mosqiiito is diurnal and hardly ever bites at night, is an error 

 which must be destroyed. Still stronger than this categorical statement is the 

 third of their conclusions {I. c, p. 705), where, concerning the transmission of 

 yellow fever by calopus, they say : " Que cette transmission n'a pas lieu en plein 

 jour pendant que le soleil est sur I'horizon." * This expression is preceded 

 by another, equally dogmatic : " dans la nature la transmission s'effectue ordi- 

 nairement la nuit. Peut-etre meme cette regie est-elle absolue." f 



In these assertions the French commission have made a complete inversion of 

 values ; their " rule " is certainly the exception. The conclusions of the French 

 investigators are based upon insufficient and faulty data, as will be shown in the 

 following. Furthermore, it appears that they were influenced in formulating 

 their conclusions by the often repeated assertion that, at Eio de Janeiro, persons 

 who visited the yellow-fever zone in the daytime only, remained free from 

 infection. 



The assertions of the French investigators were discussed and fairly refuted 

 by Dr. Ivo Bandi, of Sao Paulo, immediately after their publication. Neverthe- 

 less, they have been widely accepted and in view of their great importance in 

 connection vrith yellow fever we are under the necessity of thoroughly analyzing 

 the French observations. 



* " That this transmission does not occur during the daytime while the sun is ahove the 

 horizon." 



t " Under natural conditions transmission ordinarily occurs at night. It may be that this 

 rule is absolute." 



