

TRANSMISSION OF DISEASES BY INSECTS 259 



Ficker recovered typhoid bacilli from flies twenty-three days after 

 they had been infected. 



In fact, a great amount of evidence has accumulated proving that 

 flies transmit not only the bacilli of typhoid fever, but many other 

 bacteria, and often in enormous numbers. For example, Esten and 

 Mason in their study of the, sources of bacteria in milk, collected and 

 examined flics from stables, pig-pens, houses and other places, and found 

 an average of 1,222,570 bacteria per fly; the majority of these being 

 objectionable kinds of bacteria. 



Musca Domestica. A single female of the common house fly lays 

 in all some six hundred eggs. In midsummer, in Washington, D. C., 

 the eggs hatch in about eight hours; the larval period is from four to 

 five days and the pupal period five days, making the cycle about ten 

 days in length. In cooler parts of the season the cycle requires more 

 time and in warm climates it may be as short as eight days. The 

 number of generations in Washington is probably not more than 

 nine (Howard). 



Control. One of the best baits for flies in houses is formalin, which 

 is poisonous to flies but harmless to man. This is prepared by diluting 

 formaldehyde with five or six times as much water and exposing it in 

 shallow dishes, the addition of a little sugar or milk making the solution 

 more attractive to flies, which drink it and quickly die. Pyrethrum is 

 effective against flies, but only when it is pure and has been kept from 

 exposure to the air. Pyrethrum, the chief basis of all the common 

 insect powders, is applied by being puffed through a bellows or by being 

 burned. The powder may be moistened and shaped into cones which 

 when lighted at the top burn slowly and give off fumes that are suffocat- 

 ing to insects. 



Dr. Howard estimates that more than ten million dollars are spent 

 every year in screening houses in the United States. Another enormous 

 sum is spent for fly papers and fly traps. The efficient way to deal with 

 the fly problem, however, is to prevent the insects from breeding. Ex- 

 crementitious substances should be enclosed in such a way as to prevent 

 the access of flies, or should be treated in a way to kill the larvae therein; 

 one of the simplest methods of treating stable manure being to spread 

 it out to dry, since the maggots cannot develop without moisture. 



For detailed information on everything of importance relating to 

 the house fly, and particularly on the mitigation of the fly-nuisance by 

 concerted action in communities, Dr. Howard's admirable book on the 

 house fly should be consulted. 



