INSECTS AND DISEASE 
The spoiling of foods may obviously be hastened by ordinary 
putrefactive germs introduced in such ways and, if the fly has been 
feeding upon human discharges (tuberculous sputum for example, or 
the contents of an outside closet used by an incipient typhoid case) 
specific human diseases may easily result. 

Fig. 10. BACTERIAL COLONIES DEVELOPED ON AN AGAR 
PLATE FROM GERMS PLANTED BY THE FEET 
OF A FLY WHICH WALKED OVER IT 
The number of microbes actually carried by flies varies greatly 
with the general amount of filth in their surroundings. Studies made 
by the New York Association for Improving the Condition of the 
Poor gave an average of 13,986 bacteria per fly (on the outer surfaces 
of its body) in clean localities, against 1,106,017 in dirty surroundings. 
The germs of typhoid fever and Asiatic cholera have been isolated 
from the bodies of flies caught during epidemics of these diseases, 
and we have, in our museum of living bacteria at the American 
Museum, one strain of typhoid bacilli isolated in this way in the 
course of an outbreak in New Jersey. 
17 
