22 THE IMPORTANCE OF DOMESTIC FLIES 



bacilli, identical with those described by Morgan, in the 

 intestines of house-flies found during the summer in 

 New York ; and this bacillus is as pathogenic and as 

 dangerous as that found by Morgan in London. 

 There are excellent reasons, therefore, for fly-reduction. 

 But many more might be cited. The transmission of 

 cholera, of tuberculosis, by flies have been mentioned 

 and make these insects doubly dangerous. It is 

 possible also that the fly plays sometimes a similar part 

 in the spread of leprosy and anthrax. Typhoid fever 

 and infantile enteritis are very important to us in 

 England, because they are diseases which do direct 

 damage to us at home ; tuberculosis is being reduced, 

 and cholera and dysentery are affections now of other 

 climes. The Egyptian ophthalmia is possibly conveyed 

 by flies. So there are reasons enough for undertaking 

 fly-reduction. It is easier and better to prevent flies 

 and to inhibit these diseases than to kill a few insects. 

 But before flies can be reduced in numbers something 

 must be known of where they breed and how they 

 live ; for until the habits of animals or insects are 

 known it is impossible to get rid of them or even to 

 reduce their numbers. 



After this book was written news has arrived that 

 Professor Resenau, of the Harvard Medical College, 

 has made experiments which tend to show that the 

 virus of infantile paralysis can be conveyed from 

 child to child by aj biting fly, Stomoxys calcitrans. 

 This fly resembles the common house-fly in size and 

 naked-eye appearance; but it differs inasmuch as it 

 has a pointed proboscis, with which it can pierce 

 the skin and suck blood. This fly breeds in stable- 

 dung like the house-fly, and measures against the 

 latter should result in the extermination of the 



