FLIES AND BACILLI 179 



not pass into the body of the fly, neither do they 

 undergo any part of their life-history in its tissue. 



Dr. Sandilands* has recently investigated outbreaks 

 of epidemic diarrhoea. He points out that the preva- 

 lence of diarrhoea follows the earth's temperature, and 

 does not follow the temperature of the atmosphere. 

 It is a well-known fact that this illness is more preva- 

 lent in the houses of the poor than in the mansions of 

 the rich. As Dr. Newsholme, late Medical Officer of 

 Health for Brighton, said : 



' The sugar used in sweetening milk is often black with flies 

 which have come from neighbouring dust-bins or manure 

 heaps ; often from the liquid stools of diarrhoea patients in the 

 neighbouring houses. Flies have to be picked out of the half- 

 emptied can of condensed milk before it can be used for the 

 next meal. When we remember the personal uncleanliness of 

 some mothers, and that they often prepare their infants' food 

 with unwashed hands, the inoculation of this food with virulent 

 colon bacilli of human origin ceases to be a matter of surprise.' 



Compared with cow's milk, which nourishes a very 

 numerous progeny of bacteria, the bacterial content of 

 Nestle's milk is very low, according to Dr. Sandilands. 

 In certain seasons the cow's milk is exposed to 

 temperatures which favour an enormous multiplication 

 of bacteria, and yet it is not then a frequent source of 

 diarrhoea — in fact, mere numbers have little or no 

 influence on the incidence of the illness. The greater 

 number of cases are due to infection conveyed from 

 some patient in the near neighbourhood and conveyed 

 mechanically by flies. 



The great attraction of the sweetened condensed 

 milk for flies to some extent explains the greater 

 prevalence of infantile diarrhoea among children fed 

 on this preparation. 



As was stated above, one of the most remarkable 



* Journal of Hygiene, vol. vi., 1906, pp. 77-92. 



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