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it was found that a room situated between one of the cowsheds and some stables invariably yielded far
more flies than did the cowshed itself. A like experience, moreover, is recorded in respect of Centre 12,
where the occurrence of an exceptional degree of fly nuisance in a particular room was undoubtedly due
to a large collection of stable manure in the near neighbourhood.‡ The importance of securing
speedy removal of horse manure from near proximity to inhabited houses is, it will therefore be
seen, particularly emphasised by the experience gained during this enquiry.
Diagram III. shows the relation of temperature conditions and diarrhæa mortality to the fly curve.
A study of the amount of diarrhoea sickness occurring in the several areas surrounding the twelve centres
was contemplated when the enquiry was commenced, and the co-operation of the medical officers of
health of the boroughs in which the centres are situated was sought in making this investigation. It
soon, however, became apparent that the coolness of the summer would cause the diarrhæal mortality
to be considerably below the normal amount, and, as a matter of fact, it proved to be exceptionally low.
The number of deaths recorded from diarrhæal disease, during the thirteen summer weeks ending with
the close of the first week in September was less than one-seventh of the mortality recorded during the
corresponding period of the year 1906—331 deaths in 1907 as compared with 2,588 deaths in the
preceding year.
Enquiries were instituted on a comprehensive scale by Dr. Brown in Bermondsey, and Dr. Millson
in Southwark, with a view to ascertaining the number of cases of diarrhoea occurring in the areas surrounding
two of the twelve centres already referred to, for it was recognised, of course, that the
number of cases constitutes a far more precise test of the amount of diarrhoea than does the number of
deaths. The small degree of prevalence of the disease will be sufficiently indicated when it is
stated that in a considerable area, surrounding Centre 10 in Southwark, with a population of between
8,000 and 9,000 persons, the result of the house to house enquiry instituted by Dr. Millson showed that
only 50 cases of diarrhoea occurred during the hottest months of the summer. Among these 50 cases
there were only six in infants less than one year of age, and the six babies all recovered. The fact that
among nearly 9,000 persons, occupying one of the poorest areas in London, not a single death from
infantile diarrhoea occurred during the four hottest weeks of the summer of 1907, is sufficiently indicative
of very exceptional meteorological conditions.
The question of the relation of enteric fever and summer diarrhoea to fly prevalence has during
the last few years been made the subject of some study.§ It has been shown by several investigators
that the temperature curve, fly curve, and diarrhæa curve stand in remarkable relationship one
with another. The fact that during the hot weeks of the year the temperature curve and
the diarrhoea curve show a rough correspondence, and that the similarity of the variations of
the curves is exhibited in a marked manner when the figures for a number of years are
passed in review, has, of course, been long well known. Dr. Ballard showed that this
correspondence was more precise if, instead of dealing with the ordinary air temperature, that of
the earth four feet below the surface be used in plotting out the temperature curve, and he was disposed
to think this fact meets its explanation in an hypothesis that the cause of diarrhoea is some living
organism finding specially favourable conditions for growth in the superficial layers of the earth.
It has been pointed out, however, that the curve of "earth temperature" of necessity lags a little
behind that of "atmospheric temperature,for heat takes time to penetrate three or four feet beneath
the surface; and it has been urged that in like manner the rise of diarrhæal mortality of necessity lags
a little behind the rise in the total amount of diarrhæal disease. It may well be argued, therefore, that
the correspondence noted by Dr. Ballard is, after all, no more than a chance coincidence, the rises in
the "earth temperature "curve and in the "diarrhæal curve" being merely due to one common
cause—"hot weather."
In the same way, it is open to argument that the correspondence between the fly curve and the
diarrhæa curve is a mere coincidence; in other words, that both simply result from the influence of temperature,
and that there is not, in point of fact, any causal connection between flies and diarrhoea. Thus
Dr. Niven, of Manchester, who was one of the first to devote attention to the subject, wrote, in 1903,
"So far, not a shadow of evidence has been adduced, unless it be the absence of other ascertainable
means of transport. Yet the proposition is not one that we can positively reject. Warm weather
brings flies and warm weather brings diarrhoea about the same time." Dr. Niven hass hown, on the
other hand, that the correspondence in the two curves is of a fairly precise character, and has urged
that when the dates of onset of fatal illness " are used for plotting out the diarrhoea curve, the fly
curve is found to ante-date, by a few days, the rise and fall of the diarrhoea curve in Manchester (see
Annual Report for 1905); further, he finds, when the number of flies caught day by day in different
parts of Manchester is studied, that there appears in the several localities "a tendency for an increased
number of flies to precede an increase in the commencement of fatal cases by a period of three or four
days " (loc. ext. p. 150). The difference in dates was so small in 1904 and 1905 (see Diagram III.) that
‡ These three examples are all taken from places of observation surrounding centres belonging to the group
not pre-eminently associated with collections of horse manure.
§ Dr. Niven, of Manchester, who has been a pioneer in these investigations, has, moreover, in his annual report,
1905, drawn attention to the need of enquiry as to whether there is an excessive incidence of diarrhæal mortality
upon infants living in close proximity to stables. It had been intended to investigate this subject in the twelve
areas with which this report deals, but the coolness of the summer effectually prevented this being done. Dr.
Harris, of Islington, has, indeed, made some enquiry as to the extent to which diarrhæal mortality prevailed during
the third quarters of 1903-07 in the neighbourhood of stables in his borough, but his results are, on the whole,
negative. As long ago as the year 1900, Dr. F. J. Waldo, in his Milroy Lectures on Summer Diarrhoea, raised
question as to whether horse dung was answerable to any extent for the causation of the disease. The trend of his
argument was in favour of acceptance of this view, but he notes that there does not, so far as can be ascertained,
appear to be excessive incidence of diarrhoea upon the families of stablemen who live in mews. He quotes, moreover,
Dr. Orme Dud field's opinion to a like effect.