264 MOSQUITOES OF NORTH AMERICA 
between eight and eleven o’clock at night, in a room in his house or in his office 
atthe Museum at Parad, 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 Rio 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 was 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 !’Institut Pasteur, vol. 17, 1903, p. 691) 
assert that Aédes 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 mosquito 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 (1. ¢., p. 705), where, conce1riug 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 Vhorizon.” * This expression is preceded 
by another, equally dogmatic: “ dans la nature la transmission s’effectue ordi- 
nairement la nuit. Peut-étre méme cette régle est-elle absolue.” + 
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 Rio de Janciro, 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 with yellow fever we are under the necessity of thoroughly analyzing 
the French observations. 
‘ ae That this transmission does not occur during the daytime while the sun is above the 
horizon.” 
+“ Under natural conditions transmission ordinarily occurs at night. It may be that this 
rule {s absolute.” 
