158 SUMMER DIARRHCEA 



for fly carriage. (9) No real evidence has been produced against 

 the fly theory." 



Peters also produces evidence to show that flies do not bring 

 infection from the manure heaps in which they have been bred. 



Several previous observers had expressed the opinion that 

 flies spread summer diarrhoea, amongst others Fraser (1902), 

 Nash (1903, 1904), Copeman (1906), Shell (1906) and Sandilands 

 (1906), held strong views on the subject. Newsholme (1903, 

 p. 21) thinks that food in the liouses of the poor can scarcely 

 escape faecal infection. " The sugar used in sweetening milk is 

 often black with flies, which may have come from a neighbouring 

 dust-bin or manure heap, or from the liquid stools of a diarrhoeal 

 patient in a neighbouring house. Flies have to be picked out of 

 the half empty can of condensed milk before its remaining 

 contents can be used for the next meal." He considers that the 

 greater prevalence of diarrhoea among infants fed on Nestle's 

 milk is due to the fact that flies are more attracted to it than 

 to ordinary cow's milk on account of its sweetness. The 

 investigations of Lewis (191 2, p. 276) are speciall}' interesting in 

 this connection. Out of twenty-eight samples of milk bacterio- 

 logically examined seventeen showed non-lactose fermenting 

 bacilli, and in six of these the bacilli were of the same variety as 

 had been found in the faeces of the children for whom the supply 

 was provided. 



Several interesting observations have been made on this 

 subject in other parts of the world. Ainsworth (1909), though 

 dealing with very small numbers of cases, shows clearly by 

 means of a chart the close correspondence between the numbers 

 of flies and the cases of diarrhoea in Poona, India. Peters (1909) 

 has pointed out that in Melbourne, Australia, the epidemic often 

 declines notwithstanding the fact that the temperature may 

 continue to rise for several weeks. This may be attributed in 

 part to exhaustion of susceptible material, and in part to the 

 effect of the extremely hot dry winds which are very fatal to flies 

 both in the larval and imago stages. 



Whatever part flies may play in the dissemination of the 

 disease direct infection and carelessness must always be factors 

 of great importance. 



