HABITS 8 1 



hatched out ; this gives an average of 720 for each stool." 

 These flies belonged to six species, DrosopJiila inelanogaster Mg., 

 Liniosina piinctipennis Wied., Sepsis sp., SarcopJiaga aurifinis 

 Walk., SarcopJiaga sp., and Sarcop/iagula sp. The undetermined 

 SarcopJiaga and the DrosopJiila are frequently found upon food, 

 and the others, with the exception of the Sepsis, have occasionally 

 been found upon provisions in houses. They are all liable to 

 infect water supplies especially in dry weather. Reference to 

 Chapter xxvi will show that the number of species that visit 

 or breed in human excrement is very large. 



Particular attention may, however, be directed to one of the 

 species just mentioned, L. piuictipennis, which occurs throughout 

 the tropics, and to flies of the genus Pycnosoma. 



In regard to L. punctipennis, Nicholls (p. 86) makes the 

 following interesting statement : 



" Limosina punctipennis Xxwes and breeds almost exclusively 

 upon human excrement, and in exposed places swarms of these 

 little flies will be found. The only other situations in which 

 I have caught it have been water pools, rivers and ravines in 

 very dry weather, when it will fly a considerable distance in 

 search of water. After a long period of dry weather I placed a 

 small pan of water in a patch of ' bush ' to which labourers were 

 accustomed to resort, and in which these flies were consequently 

 plentiful. Soon numbers of them were seen alighting on the 

 vessel at the edge of the water and drinking ; the next nearest 

 water was 100 yards away and here also the flies were seen. 

 The pan of water was left here for several hours ; it was then 

 removed and examined for faecal contamination by means of 

 cultures, and Bacillus coli comniunis was obtained. This 

 experiment was repeated upon two other occasions, and in one 

 of these the same organism was grown. Needless to say that 

 both the vessel and the water were sterilised, and control 

 samples were kept in sterilised bottles." 



Especially in Africa and the East, flies of the genus Pycnosoma, 

 which have habits similar to those of the house-fly, may carry 

 disease organisms, especially B. typJiosus. They swarm about 

 filth trenches, and seem to breed in faecal matter and offal of all 

 kinds (see Chapter Xlll). 



G.-s. 6 



