42 



the whole number of flies captured in kitchens and dining rooms, and 

 while it was by no means one of the species most commonly captured 

 upon excrement, it was shown conclusively that under certain condi- 

 tions this insect may be a factor of the greatest importance in the 

 spread of intestinal disease. In the most cleanly and best cared for 

 portions of a large city these conditions do not exist. The admirable 

 water supply and sewerage systems pertinent to such localities — the 

 admirable water-closet facilities which sanitary plumbing has carried 

 to such a degree of excellence — obviate in a large measure typhoid- 

 transfer possibilities, yet. even in such places, where the vessels used 

 in the sick room are not promptly disinfected and where by reason of 

 neighboring stables house flies are especially abundant (since these 

 creatures breed by preference in horse manure), the possibility may 

 still exist, but in army camps where faeces are left exposed the house 

 fly will and does breed in this substance in large numbers and in 



Fig. 21. — Drosopldla ampelophila: a, adult; b. antenna of same: e, base of tibia and first tarsal joint of 

 same: d, puparium, side view: e, puparium from above; /, full-grown larva; g, anal spiracles of 

 same (author's illustration). 



towns where the box-privy nuisance is still in existence (and this 

 applies to very many farmers' houses in the country) the house fly is 

 a constant source of danger. Moreover, in the low quarters of a 

 large city where there is lax sanitary supervision, in the open lots 

 surrounded by an ignorant population, faeces are frequently deposited 

 in the open, sometimes in close proximity to kitchens, and thus may 

 become very dangerous. 



The other species of flies which are of especial importance are as 

 follows: The little fruit flies of the genus Drosophila. and especially 

 DrosopMla ampdophila (tig. 21). which is so commonly found in 

 houses in the autumn, attracted to overripe or partly decaying fruit. 

 and which sometimes swarm in great numbers about the fruit stands in 

 markets, is also an excrement breeder, and at certain times of the year 

 becomes an important form in the disease-transfer relations. The 

 species known as the little house fly (Homalomyia canicularis and If. 



