MODE OF ATTACK 261 
higher temperature of persons stricken with fever might be an additional attrac- 
tion for the mosquito. 
The French commission found that calopus has a decided predilection for 
the blood of man. It can, however, subsist upon the blood of any warm-blooded 
animal, but it shows a more or less pronounced repugnance for any other warm- 
blooded animal than man. Durham states that at Pard he has observed calopus 
feeding upon “ dogs, on an agouti, and a bat,” but he does not indicate whether 
this was in freedom or with mosquitoes in captivity. Neumann, in his experi- 
ments on the transmission of Plasmodium precox to canary birds by means of 
calopus, found that this mosquito showed a decided preference for mammalian 
blood. In his experiments, conducted under the most favorable conditions, 
from a total of 2573 female calopus, he was only able to induce 789 to suck blood 
of canaries, or 30.7 per cent. With Culex, on the contrary, 64 per cent of the 
females attacked the birds. When the experiment was made with rats the re- 
sults were reversed and the calopus attacked at once while the Culex showed 
Tepugnance. 
It appears also that calopus discriminates between races and individuals. This 
was already discussed by Finlay in the following manner: 
“Finally, should be taken into account the preferences which mosquitoes 
manifest towards certain races and individuals; one notes that the least tor- 
mented race appears to be the African and the individuals most persecuted by 
them are those of northern races who have recently come to the tropical regions 
of America. It appears probable that this depends upon the thickness of the 
skin and upon the condition of the capillary circulation of the skin; it is to be 
assumed that these circumstances will affect the facility with which the female 
mosquito can obtain the blood which it needs to complete its life-cycle.” 
The French investigators made a number of experiments to show whether 
calopus bites indifferently people of different races. They concluded that it 
easily bites both the negro and the red-skinned races, but that it has a marked 
predilection for the white race. If mosquitoes of the same age and at the same 
temperature are placed upon individuals of the black-skinned, red-skinned and 
white-skinned races, the white will be bitten most quickly. The red-skin is also 
quickly attacked. Towards the negro, calopus shows some repugnance, and 
almost never in the course of their observations did it decide to bite immediately, 
and often a contact of ten to fifteen minutes was necessary before the proboscis 
was inserted. They show also that among the individuals of the white race, this 
mosquito has preferences, and attacks with the greatest avidity young, vigorous 
individuals of fine skin and good color rather than anemic or aged persons. 
When it is hungry, however, the mosquito will bite the first human being it 
meets. 
The stealthiness of attack has already been mentioned as a peculiarity of the 
yellow-fever mosquito. This is brought out in an interesting manner by Parker, 
Beyer and Pothier in the results of their investigations at Vera Cruz (Report of 
Working Party No. 1, Yellow fever Institute, Bulletin 13, March, 1903) : 
“The approach to attack of Stegomyta is extremely insidious, usually ap- 
proaching an individual on the shady side and without warning. The perti- 
