The house fly : Musca domestica, Linnæus a study of its structure, development, bionomics and economy / by C. Gordon Hewitt.

  • Hewitt, C. Gordon (Charles Gordon), 1885-1920.
Date:
1910
Catalogue details

Licence: In copyright

Credit: The house fly : Musca domestica, Linnæus a study of its structure, development, bionomics and economy / by C. Gordon Hewitt. Source: Wellcome Collection.

    232/256 (page 177)
    distributed than ever before—the amount of diarrhma, instead of showing early and rapid decline, would still be increasing. It would almost appear that the advocate of the ‘ fly-borne diarrhoea hypothesis ’ must necessarily fall back in support of his theory upon the hypothetical organism, conveyed by the fly, which he may claim is affected by temperature in such a way as to bring about correspondence betAveen the diarrhoea curve and the fly curve. The very closeness of the correspondence between these two curves may indeed from this point of vieAv be thought of as constituting a difficulty rather than a point in favour of the hypothesis that summer diarrhoea is caused by flies/' [The italics are mine.^—C. G. H.] IS'o one, I think, would argue this. What is argued is that there are excellent grounds for belieAnng that flies carry the infective organism or organisms of summer diarrhoea. Niven (1904) suggested that the explanation of the falling off of the diarrhoea cuiwe while the number of flies still remain large might be due to the exhaustion of susceptible material. The one point Avhich does not appear to be considered and which, I think, will explain this seeming objection is the great susceptibility of flies to changes of temperature, which fact all who have studied closely the habits of .1/. domcstica and its allies will admit. When the temperature falls, flies become more sluggish and retire more into the shelter of houses and other buildings, although their numbers may still be considerable. It is necessary, therefore, to study the temperature curA^e in addition to the fly and diarrhoea curACS. If this is done, it is usually found that the fall in the number of flies is preceded by a fall in the temperature and that these two cuiA-es are associated closely, that is, the numerical activity of the flies—since the numbers caught are more indicatiA'e of their numerical activity than of their numerical occurrence—is dependent upon the temperature.