110 CIVIC BIOLOGY 



The evidence we have indicates that almost all dysentery and 

 summer complaint (millions of cases and 56,000 deaths annu- 

 ally) are caused directly by the house fly. One third of the 

 typhoid (about 300,000 cases and 30,000 deaths) is estimated 

 to be caused by flies, and an unknown and unknowable pro- 

 portion of tuberculosis, spinal meningitis, and other filth infec- 

 tions. Thus it is quite possible that flies carry the infections 

 which cause from 70,000 to 100,000 deaths annually. About 

 2 people in the United States die yearly from bites of poisonous 

 snakes ; rabid dogs bite about 100 with fatal effect. Can you 

 think of a more deadly animal than the common typhoid, or 

 filth-disease, fly ? 



Spread of animal diseases. An additional factor is the prob- 

 able causation of disease among domestic animals. As they 

 are not even partially protected by screens, and flies swarm 

 about their foods, epidemics of such diseases as fowl and 

 hog cholera, bovine and fowl tuberculosis, and foot-and-mouth 

 disease are almost certainly spread by flies. This matter has 

 not been investigated as it should be, but we are likely to 

 see a remarkable clearing up of animal diseases as soon as we 

 exterminate flies from our farms. 



Futility of fly screens. Finally, a minor consideration is the 

 (estimated) $12,500,000 we pay annually for screen windows 

 and doors, which are not only expensive but disagreeable at 

 best. These do not solve the problem, even if they did keep 

 the pests out of our homes. We must prevent flies from 

 contaminating foods on the farms and in the stores and mar- 

 kets of our cities. Thus the fight against the common enemy 

 must be community- wide, and, since one careless or ignorant 

 household can breed flies enough to infest all the houses within 

 a quarter of a mile, positively every one must cooperate. 



Need of universal cooperation. The general situation, espe- 

 cially the relations between country and city, is shown so 

 clearly in the following case that we quote in full from the 



