174 
Nature's Scavengers. [April, 
of putrescent matter and germs might be expected to 
abound, and where flies— according to the theory we are 
discussing — should have been fat and plentiful. In the 
kitchen and the dining-room they were found in about their 
usual amount, but in the room which we had selected for 
our study, and where no articles of food were ever brought, 
they were strikingly rare. 
We happen, also, to know a chemical laboratory situate 
in the basement story of a large block of buildings. The 
sanitary arrangements of the premises are imperfect, and 
sewage gases often force their way up the sink in spite of 
traps. Yet flies are here very scarce. There is no draught 
to banish them, but there is nothing to gratify their well- 
known “ sweet tooth,” and consequently they keep away. 
It may be argued that the flies would be expelled by acid 
and corrosive vapours.* This, however, is out of the 
question, as all operations involving the liberation of such 
products are conducted in an evaporation-niche of the most 
approved design. 
Again, we have every reason to suppose that the air of 
sewers, of covered manure-vaults, and of dirty negle<5ted 
cellars, should be pre-eminently rich in floating germs or 
cells, and in particles of putrescent matter. Yet flies care- 
fully avoid such localities. Indeed, to darken an ordinary 
apartment — a step certainly not calculated to improve its 
sanitary condition — is one of the most approved methods of 
banishing these intruders. 
It may further be remarked that flies, when soaring about 
in a room, do not visit every part of the space as an animal 
might be expected to do which was collecting food. They 
hover backwards and forwards, or wheel round in a circular 
or elliptical orbit in some given spot, often selecting as their 
centre the bottom of some suspended objeCt, such as a bird- 
cage, a gaselier, or the like. They rather avoid the corners 
of the room. All this is exceedingly unlike the movements 
Jnsedts do not, as might be supposed, invariably shun localities where acid 
gases and vapours are evolved. The writer has seen the woodwork of old and 
leaky vitriol-chambers, softened by exposure to atmospheric influences, aided 
by the frequent escape of sulphurous acid, selected by the wasps and hornets 
of the neighbourhood as an excellent source of fibre for the paper-work of 
their nests. In a much-decayed beam of this kind were found a large number 
of Coccinella j-punctata. In dye- and print-works, during the summer and 
autumn season, moths are frequently found drowned in bowls of acid solutions 
of tin. Gnats have been perceived dancing merrily, and to all appearance 
unharmed, in the orange vapours escaping from a shed in which nitrate of iron 
was being made. On the other hand, a shed, which had been sele&ed for the 
preparation of solutions of tin, and which had evidently been the home of 
numerous spiders, displayed, after a few months, merely the tattered remains 
of old and untenanted cobwebs. 
