256 



THE RELATION OF FLIES TO SUMMER DIARRHOEA 



were made from July (in one year from the end of May) until 

 November during the years 1904, 1905, 1906, 1908 and 1909. 

 The complete data obtained are given ; these include for each 

 week the number of flies captured, the number of deaths from 

 diarrhoea, the number of fital cases commencing, mean tempera- 

 ture in the shade, rainfall in inches, and the underground 



July August September October 



9 16 23 30 6 13 20 27 3 10 17 24 1 8 1 5 22 



Numerical Asunoance of Flies. 

 Deaths f"ro,-*i Oiarrhcza. 

 Fatal Cases commencing. 



Fig. 99. Chart illustrating the relation of the numerical abundance of house-flies 

 to summer diarrhoea in the city of Manchester in 1904. Prepared from 

 statistics and chart given by Niven. 



temperatures at 1 foot and 4 feet respectively. From these data 

 charts are constructed. I have prepared Figs. 99 and 100 from the 

 statistics and chart given for the years 1904 and 1909. Although 

 in Fig. 99 the temperature curve has been omitted, it may be 

 pointed out that in Niven 's charts there is no direct relation 



