172 Nature's Scavengers. [April, 
be surprised at such a choice in an age which has produced 
Kingsley’s “ Ode to the North-east Wind,” and certain 
attempts to “ rehabilitate ” the characters of Robespierre 
and of Henry VIII. It was first asserted that the gambols 
of the fly in the air of a room were to be compared to the 
evolutions of the bat or the swallow ; that it was, in faCt, 
hawking for food, and that it caught on the wing and swal- 
lowed both any suspended particles of putrescent matter 
and those animal and vegetable germs which are now be- 
lieved to play an important part in the propagation of 
zymotic disease. To this the reply is very simple and very 
conclusive. The mouths of creatures which hawk for food 
— such as the bat, the swallow, and the goatsucker — are 
characterised by their wide gape. They are open traps, 
which are borne rapidly against the intended prey, and at 
once close upon it. The mouth of the house-fly, on the 
contrary, is a narrow tube, admirably fitted for pumping or 
sucking up fluids or semi-fluids, but utterly unsuited for 
seizing small solid bodies suspended in the air. The evolu- 
tions of flies, therefore, are to be compared rather with the 
flight of the pigeon than with that of the swallow ; they are 
probably undertaken merely as an amusement, and the occa- 
sional collisions between two flies do not arise from their 
both making a simultaneous swoop at the same germ, but 
are entirely sportive in their character. 
Scarcely, however, have the claims of the house-fly as an 
aerial scavenger been got rid of by this consideration, than 
they are re-introduced under a modified form. We read in 
Hardwicke’s “ Science Gossip ” for October, 1875, that a 
chemist was struck with the faCt that flies, after soaring 
about in the air for a time, alighted, and wiped their feet, 
wings, and bodies, with very great care. Observing the 
process under a microscope, he found that a number of 
minute germs adhered to the body and limbs of the fly, 
which it thus stripped off, and finally devoured. He next 
discovered that the flies in well-ventilated rooms were 
always lean, whilst those in ill-ventilated places were fat 
and well-nourished. Upon these observations he founds the 
practical recommendation that housewives should not set 
poisonous mixtures for flies, but should merely cover up 
carefully all articles of food, and seek to get rid of the 
visitors by careful ventilation. This discovery is brought 
under the public notice as a confirmation of the “ pious 
adage that every thing is of some use.” 
Now, that flies are in the habit of cleansing their legs, 
wings, and bodies, is a very old faCt. They perform the 
