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.

    23/52 (page 21)
    particles met with are of various sizes and irregular shapes, but they rarely exceed *04 mm. in diameter. It would thus appear that when flies feed on fluids or soluble solids such as sugar, the food is first sucked into the crop, and when this is full it passes into the intestine directly, as noted by Graham-Smith. Insoluble solid food, however, is probably taken directly into the intestine. This suggests that the fly is able to exercise some voluntary control over the passage of food into the crop or the intestine respectively. The feeding of fly larvae was studied specially in regard to their behaviour towards round worms. The voracity with which larval flies feed is well known, and the increase in their size from day to day is remarkable. They appear to be as omnivorous as adult flies. When fresh round-worms were offered to the larvae, they were at once attacked. The larvae swarmed over the worms, nibbling at them with great vigour. They seemed, however, quite unable to penetrate the tough cuticle unless there were a crack or a small tear, and, if other food were not provided, the larvae died. On the other hand, when the worms were cut or broken before being introduced, the larvae devoured the internal parts with extraordinary rapidity. Starting at one end of a broken piece, they would eat their way right through to the other end leaving nothing but a tube of cuticle. In this way half a dozen larvae would devour, within two or three days, a large worm 20 or 30 times their own bulk. On examining larvae which had fed on female egg-bearing worms, large numbers of eggs were found surrounding the larvae but not actually sticking to them. On examining the intestine of the larvae no intact eggs were ever found, but numerous fragments of shells were always recognisable. No embryonic worms in any stage were seen, From these experiments I am convinced that even full-grown larvae are unable to swallow unruptured eggs as large as those of the worms used (’07 mm.). Methods. The common house-fly, Musca domestica, was used almost ex- clusively. Only a few experiments were made with the lesser house-fly, Fannia canicularis, and the blow-fly, Calliphora erythro- cephala. In most cases the flies were obtained from the surrounding locality, but artificially-reared flies were used on several occasions. For the experiments a large cage was constructed. All the sides were made of perforated zinc, except one, which consisted of a large sheet of plate-glass; this was fixed in two grooves and could be removed. The bottom was of plain zinc. The dimensions of the cage were 3 ft. x 1^ ft. x 1 ft. It was divided into two by a partition of perforated zinc in which was a sliding panel, by which communication could be made between the two compartments. Each compartment was further furnished with a sliding door at the bottom of one side for the admission of flies, and another door at the top, through which they could be removed. For the latter purpose a small square cage with a sliding door was used. This fitted the door in the top of the large cage, and the two sliding panels could be