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was not uniform, but varied from some six or seven places to as many as twenty-nine : and as furthermore
the distances from the centres, of the places of observation chosen, were not precisely the same, it
is clear that some method of applying correction to the crude figures must be made, if it is desired to
compare results relating to the different centres. It was felt to be necessary in making such correction
to have regard both to the number of places of observation and to the degree of concentration of
these places about the centres chosen, for obviously if they cluster closely around the centre, any influence
the centre may exert would be likely to be more manifest than if they were widely scattered.
The plan adopted was to determine for each centre of observation a particular number, to be
used as a divisor and applied to the crude figures representing flies caught. This number it was on
consideration decided should be obtained by adding together the places of observation at less than 100
yards multiplied by 4, those between 100 and 150 yards multiplied by 3, those between 150 and 200
yards multiplied by 2, and, finally adding the number distant more than 200 yards.*
The gross figures for each centre were then divided by the divisors thus obtained, with the result
that the twelve curves shown in Diagram II. have been plotted out: these curves, it is claimed, fairly
admit of comparison one with another. A study of this diagram shows at once that the two offensive
trade premises, the Knacker's Yard and Gut Scraper's premises,† chosen as centres for observation,
yielded only a small number of flies in comparison with other centres.
The places of observation around the Jam Factory showed an excessive number of flies during the
latter part of August and early part of September, and, again, during the early part of October. These
increases did not correspond with the general increase in the number of flies throughout London, for
the former precedes, and the latter follows after, it. It is probable, though it has not been possible to
definitely ascertain the fact, that the prevalences in the neighbourhood of the Jam Factory were to some
extent influenced by variations in the amount of work being done there.
In the neighbourhood of the two cowshed premises the evidence of fly nuisance was pronounced.
There were a number of stables in the immediate vicinity of one of these centres, and this disturbing
influence was no doubt not without effect.
The increase in the number of flies in the case of the Cattle Market is somewhat more marked
than in the case of the cowshed premises. A like increase is also quite apparent in the case of both
stable centres.
The four centres, however, in which the evidence of fly nuisance stands out in a most striking
way are the four depots. At Centre No. 4, where there were no accumulations other than those in the
trucks (the manure being removed direct from the cart to truck), and at Centre No. 3, at which there
were no accumulations save those in barges, the nuisance was not quite so great as at Centres Nos. 1 and
2, where the rule of not allowing deposits was not so strictly enforced; it may be further observed
that at Centre No. 1, where considerable quantities of horse manure were dealt with, the numbers of
flies were more excessive than at No. 2, to which centre nothing but house refuse and road-sweepings
were brought. Indeed the Centre No. 1 stands out pre-eminently as a defaulter upon the evidence
obtained.
The main outcome of the enquiry undoubtedly is that accumulations of horse manure and in
less degree of house dust and other refuse, promote fly nuisance in their immediate neighbourhood,
their influence being manifested in marked degree at a distance of 100 to 150 yards, and still distinctly
appreciable as far away as 200 yards, or even at greater distances. While the collection of refuse
material at a depot necessarily therefore involves production of nuisance, the observations made show
that this nuisance is doubled or trebled in intensity if the most strict adherence to the rule that deposits
should not be allowed to accumulate at the premises be not observed. The value of the Council's by-law,
which prohibits the deposit near houses of offensive refuse for more than twenty-four hours, is thus
apparent; although it is at the same time obvious that, even when the by-law is strictly complied with,
fly nuisance must none the less be experienced.
Study has further been made of the extent to which other and less potent influences than collections
of stable manure or house refuse have been operative in determining increase in the number of
flies.
(1) Domestic Cleanliness.—A dirty condition of rooms, walls and ceilings appears to favour
invasion by flies ; though, when the rooms have been "done up," it has not been found to reduce
but rather, momentarily, at any rate, to increase the number caught. The presence of crumbs
and of particles of food on floors, in crevices and upon rugs and coverings, seems to attract flies
to a much greater extent than does the mere existence of dirty walls and ceilings. It is a noteworthy
fact that where there are a number of children in a house, flies appear, other things being
equal, in larger numbers; and, in the case1 of one house, the inspector found that, when during the
course of the summer the children went away, the number of flies showed a marked reduction.
That the association is indirectly caused is shown by the freedom from flies of occupied class-rooms
of schools, a fact confirmed by experiment during this enquiry.
* The number of flies caught per place of observation for places situated at differing distances from the several
centres are as follows: at more than 200 yards, 4,300; between 150 and 200 yards away, 1,900; between 100 and
150 yards away, 5,400; at less than 100 yards, 6,700. A more precise gradation is obtained if 210 yards be taken
as the highest limit instead of 200. The figures then are: 3,500 at more than 210; 3,000 at from 150 to 210; 5,400
at from 100 to 150 each; 6,700 at less than 100. The corresponding figures for eleven of the centres (omitting a
centre at which the conditions were somewhat exceptional) were 2,200, 2,600, 4,800, and 5,700. These figures
justify some such method of computation as that above adopted.
† The Knacker's Yard showing, however, a larger number than the Gut Scraper's : this may be accounted
for by the fact that a few horses were kept, and that there was thus some accumulation of stable manure at the
former premises.