THE TYPHOID FLY, OR HOUSE FLY. 

 Table III. — Sources of bacteria from fliex. 



29 



" 2,200 mold spores. 



" From the above table the bacterial population of 414 flies is pretty 

 well represented. The domestic fly is passing from a disgusting nui- 

 sance and troublesome pest to a reputation of being a dangerous 

 enemy to human health. A species of mosquito has been demon- 

 strated to be the cause of the spread of malaria. Another kind of 

 mosquito is the cause of yellow fever, and now the house fly is con- 

 sidered an agency in the distribution of typhoid fever, summer com- 

 plaint, cholera 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 season the numbers of bac- 

 teria on flies are comparatively small, while later the numbers are 

 comparativel}^ very large. The place where flies live also determines 

 largely the numbers that the}^ carry. The average for the 414 flies 

 was about one and one-fourth million bacteria on each. It hardly 

 seems possible for so small a bit of life to carry so large a number of 

 dr^anisms. 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 quantity of steril- 

 ized water, then shake the bottle to wash the bacteria from their 

 bodies, to simulate the number of organisms that would come from a 

 fly in falling into a lot of milk. In experiments ' <:/,' ' e,' and ' / ' 



