108 THE HOUSE FLY—DISEASE CARRIER 
“From the above table the bacterial population of 
414 flies is pretty well represented. The domestic fly 
is passing from a disgusting nuisance and troublesome 
pest to a reputation of being a dangerous enemy to hu¬ 
man health. A species of mosquito has been demon¬ 
strated to be the cause of the spread of malaria. An¬ 
other kind of mosquito is the cause of yellow fever, 
and now the house fly is considered an agency in the 
distribution of typhoid fever, summer complaint, chol¬ 
era infantum, etc. 
“The numbers of bacteria on a single fly may range 
all the way from 550 to 6,600,000. Early in the fly sea¬ 
son the numbers of bacteria on flies are comparatively 
small, while later the numbers are comparatively very 
large. The place where flies live also determines 
largely the numbers that they carry. The average for 
the 414 flies was about 1,250,000 bacteria on each. It 
hardly seems possible for so small a bit of life to carry 
so large a number of organisms. The method of the 
experiment was to catch the flies from the several 
sources by means of a sterile fly net, introduce them into 
a sterile bottle, and pour into the bottle a known quan¬ 
tity of sterilized water, then shake the bottle to wash 
the bacteria from their bodies, to stimulate the number 
of organisms that would come from a fly falling into a 
lot of milk. 
“In experiments ‘d,’ ‘e,’ and T the bacteria were 
analyzed into four groups. The objectionable class, 
coli-cerogenes type, was two and one-half times as 
abundant as the favorable acid type. If these flies 
