Dr. Grassi is said (_British Medical Journal_) to have made an
important, and by no means pleasant, discovery in regard to flies. It
was always recognized that these insects might carry the germs of
infection on their wings or feet, but it was not known that they are
capable of taking in at the mouth such objects as the ova of various
worms, and of discharging them again unchanged in their fæces. This
point has now been established, and several striking experiments
illustrate it. Dr. Grassi exposed in his laboratory a plate containing a
great number of the eggs of a human parasite, the _Tricocephalus
dispar_. Some sheets of white paper were placed in the kitchen, which
stands about ten meters from the laboratory. After some hours, the usual
little spots produced by the fæces of flies were found on the paper.
These spots, when examined by the microscope, were found to contain some
of the eggs of the tricocephalus. Some of the flies themselves were then
caught, and their intestines presented large numbers of the ova. Similar
experiments with the ova of the _Oxyuris vermicularis_ and of the
_Toenia solium_ afforded corresponding results. Shortly after the flies
had some mouldy cream, the _Oidium lactis_ was found in their fæces. Dr.
Grassi mentions an innocuous and yet conclusive experiment that every
one can try. Sprinkle a little lycopodium on sweetened water, and
afterward examine the fæces and intestines of the flies; numerous spores
will be found. As flies are by no means particular in choosing either a
place to feed or a place to defecate, often selecting meat or food for
the purpose, a somewhat alarming vision of possible consequences is
raised.
* * * * *