1876.] Nature's Scavengers. 173 
operation principally when they have been partaking of their 
ordinary food, which, as we hoped was known to all the 
world, consists of something much more substantial than 
microscopic germs. That among the matter adhering to 
their surface such germs may occasionally be found, we do 
not mean to deny. Flies, in all probability, have their 
parasites, and are known to be liable to disease depending 
on a fungoid development in their bodies. That they may 
attempt to free themselves from parasites, and from the 
spores or germs of this disease, is not at all unlikely ; nor 
can we feel astonished that the filth — living or lifeless — - 
collected from the surface of their bodies is ultimately swab 
lowed. The same thing is, in faCt, done by the cat and all 
other animals which cleanse themselves by licking. But to 
assert that what the fly thus collects in the operations of its 
toilet forms an essential part of its diet, upon which the 
question of its condition depends, is about as rational as to 
declare that a cat is kept plump by the lickings of its fur. 
We know the food of the fly : we see it settling upon every 
article of our diet, and upon a great many things which not 
even a Chinaman will eat, and, with its protruded haustel- 
lum, imbibing their fluid portions ; we find it even sucking 
up the moisture of perspiration from our skins. According 
to our observation it frequents those places mainly where 
the good things of this life abound, quite irrespective of their 
sanitary condition. That, like most other insects, it does 
not love what are called “ draughty ” localities, — premises 
traversed by strong currents of wind, —is quite true. But 
let a room be perfectly ventilated, without a draught, and 
stock it with sugar, sweetmeats, and fruits, and you will find 
the flies cluster thick as leaves in Vallombrosa. On the 
other hand, we have noticed the absence — or at least the 
great rarity — of flies in rooms where no articles of human 
food were ever brought, even though the presence of atmo- 
spheric germs in an unusual degree was highly probable. 
To take one instance : — About eight years ago we became 
the inhabitant of a quaint and roomy old mansion in the 
North of England, at a mysteriously moderate rent. We 
soon found that the atmosphere — not merely of the house, 
but even of its terraced gardens — was at times unbearably 
foul, and that ventilating arrangements and disinfectants 
were alike powerless. The drainage from the cesspools of a 
group of houses situate on higher ground had soaked down 
through the shaly soil, and poisoned the ground beneath 
the foundations. Here, then, was air in which particles* 
* It may perhaps be prudent to remind all whom it may concern that 
“ particle ” is not synonymous with atom, or even with molecule. 
