Further reports (no. 4) on flies as carriers of infection.

Date:
1911
Catalogue details

Licence: In copyright

Credit: Further reports (no. 4) on flies as carriers of infection. Source: Wellcome Collection.

    10/52 (page 8)
    temperature remaining low, while rain showers were frequent, and high winds often prevailed. Nevertheless, on each occasion on which several hundred marked Hies were liberated, a certain number were subsequently recovered, within forty-eight hours or less, from human habitations in Post- wick, at points of the compass which were apparently dependent, for the most part, on the direction of the prevailing wind, and at distances ranging from 300 yards to 1,700 yards (World’s End Public House, Bramerton) from the refuse deposit. On one particular occasion on which chalk of a bright canary yellow colour was employed for marking the hies, the day being fine and sunny, with a gentle north-west breeze, the results obtained were specially interesting. Of these hies several were observed and captured by us along the stretch of river-bank between a point opposite the refuse heap and Post wick Hall, within half an hour of their liberation. Two other marked hies were caught in a large open- fronted summer-house on the lawn of Postwick Hall—a distance of 800 yards in a direct line from the point at which they were set free—one 35 minutes, and another 45 minutes after being liberated. Within the next four days, more than forty of these yellow- coloured hies were caught, on hanging hy-papers, in the kitchen and out-buildings at Postwick Hall, while isolated specimens were also trapped in various parts of the village, at greater distances, and at different points of the compass, from the refuse deposit. Of the marked hies caught on “ tangle-foot ” papers and tapes a certain proportion probably were overlooked, owing to the fact that the colour of the chalk soon gets considerably obscured by the glutinous material becoming spread over the bodies of the flies in their struggles to free themselves. On the accompanying map, sketched from the 6-inch ordnance survey, the various points at which marked flies were caught during the progress of these experiments are indicated. Many of our marked flies were seized and devoured by swallows, a number of which often appeared flying up and down the reach of the river, opposite the wharf-staging at the refuse deposit, shortly after the commencement of an experiment, even if there had been none to be seen just previously. According to local testimony swallows had been noticed in the village during the past summer in quite exceptional numbers, doubtless attracted by the excessive pre- valence of flies. But it is interesting, from the biological point of view, that they should readily take flies of a brilliant canary-yellow colour such as they can never have seen before. A few of these coloured flies that happened to drop into the water were also seen to fall a prey to fish. For the purpose of our experimental investigation these yellow- coloured flies proved most satisfactory. But owing to the fact that marked flies, after a longer or shorter interval of time subsequent to being freed, usually succeeded in removing the colour from their wings, eyes, legs and—except on the thorax—to some degree from their bodies also, they then presented the appearance of having been lightly dusted with pollen. And, although the house-fly rarely visits flowers, it appeared desirable, in order to meet possible criticism, to examine under the microscope the body surface, more