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.

    40/52 (page 38)
    were they again found on the legs, namely on the 10th day, when the flies were fed on concentrated syrup. They were still present, however, in the intestinal contents on the 16th day. Although B. pyocyaneus was constantly present in the intestinal contents of milk-fed specimens up to the 14th day, it was only found on the limbs of a single specimen on the 8th day. This specimen had fallen into the milk which was subsequently proved by cultures to be infected {see Table VII.). After making cultures from the milk on which the blow-flies infected with B. pyocyaneus had been fed on the 10th day, four blow-flies, about five days old, were allowed to feed on the remainder of the milk. A few hours later they were dissected and B. pyocyaneus was found in the intestinal contents of two of them, as shown in Table IX. Table IX.—Showing the results of cultures made from the limbs and intestinal contents of clean blowflies which were allowed to feed on milk contaminated by blowflies infected 10 days previously with B. pyocyaneus. No. of flies. Legs. Wings. Head. Intestinal contents. 1. 2. 3. 4. 5. 6. 1. 2. 1 0 0 0 0 0 0 0 0 0 + 2 0 0 0 0 0 0 0 0 0 + 3 0 0 0 0 0 0 0 0 — U 4 0 0 0 0 0 0 0 0 0 0 In the experiment just quoted the blow-flies not infrequently fell into the milk, and in this manner perhaps infected it, at least for the first few days, by means of the organisms still present on their limbs. Moreover, in attempting to clean themselves they may have reinfected their limbs from their crop contents, since they frequently applied their proboscides to their legs. Although, under natural conditions, it is a common occurence for flies to fall into fluids on which they are feeding, especially when the fluids are contained in vessels with smooth, vertical walls, it was thought desirable to attempt a series of experiments so arranged that the flies could feed on the fluids, but could not fall into them. For this purpose the following experiment was made :— Experiment 2.—About 20 blow-flies were confined in each of four cages, the flies in two of the cages being infected by feeding on an emulsion of B. prodigiosus in syrup, and those in the other two cages being similarly infected by feeding on an emulsion of B. pyocyaneus. In each instance the emulsion was placed in a watch-glass, and a short distance above it was fixed a piece of zinc pierced by round