Further reports (no. 6) on flies as carriers of infection.

Date:
1913
Catalogue details

Licence: In copyright

Credit: Further reports (no. 6) on flies as carriers of infection. Source: Wellcome Collection.

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    note oil the occurrence of the Lesser House-fly at Leeds : by Mr. Austen. (3) The part played by Flies in the dispersal of the eggs of Parasitic Worms: by Dr. Nicoll. (4) Further observations on the ways in which artificially infected Flies carry and distribute pathogenic and other Bacteria : by Dr. Graham-Smith. Determination of the possible range of flight of flies is obviously of considerable importance in relation to the question of the carriage of infection by these insects, and consequently advantage was taken of an exceptional opportunity afforded in the summer of 1910 for carrying out a series of experiments at the village of Postwick, near Norwich, in order to test this ques- tion of the range of flight. Postwick was selected on account of an excessive prevalence of flies there at that time. It was ascertained that the breeding centre of these flies was a refuse tip half a mile from the nearest point of the village and on the opposite bank of the River Yare. Numbers of flies caught at this refuse tip were liberated after having been marked for purposes of identification by dusting them with a small quantity of coloured chalk. On each occasion on which several hundred marked flies were liberated, a certain number were subsequently recovered from human habitations in Postwick, at points of the compass which were apparently dependent, to a considerable extent, on the direction of the prevailing wind, and at distances varying from 300 yards to 1,700 yards from the refuse deposit. On one occasion marked flies were caught, within 45 minutes of being liberated, 800 yards from the point at which they were set free. Dr. Nicoll’s paper on the dispersal by flies of the eggs of parasitic worms deals mainly with the results of experiments devised to ascertain to what extent, and for how long a period, flies can carry eggs by actually ingesting them and retaining them within their intestine. Dr. Nicoll, while recognising that corroboration from observa- tions under natural conditions is desirable, concludes, as the result of his experiments, that flies may convey the eggs of certain parasitic worms from excrement to food and that they may do so in two ways, namely, on the external surface of their body and in their intestine. The latter mode is practicable only in certain cases, where the eggs are of small size (under '05 mm. in diameter). On the external surface eggs of larger size (up to '09 mm. in the experi- ments) may be conveyed. Eggs adhering to the external surface are usually got rid of by the fly within a short time, but those which are taken into the intestine may remain there for two days or longer. The eggs which are conveyed in either of these ways may remain alive and subsequently cause infection. Dr. Graham-Smith’s further observations on the ways in which artificially infected flies carry and distribute bacteria indicate that both house-flies {M. domestica) and blow-flies (C. erythro- cejjhala) are able to infect fluids, such as milk and syrup, on
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