early October; the tramps and immigrants from the country generally came rather later. There can
be no doubt, therefore, that in October there were special causes favouring verminous conditions in common
lodging houses, over and above the ordinary seasonal influences, affecting such conditions in the
population at large. In other words, it may be inferred that if the curve for fleas had been obtained
from observations made on the general population, it would have exhibited a somewhat more abrupt
fall, after attainment of its maximum in the early part of September, than was actually the case.
It will be seen, then, if due weight be given to these various considerations, that the true flea
curve must be held, after attainment of a maximum in early September (35th week), to have fallen
more decidedly and suddenly than that actually shown in the diagram. In fact, the real curve
approximates more closely to the bug curve.
Question has from time to time been raised as to the possibility that fleas, bugs and lice may
transmit disease.* The autumnal high level in the flea and bug curves suggests comparison with the
curves of diseases which have an autumnal prevalence. Study of Diagram IV., in conjunction
with the notification curves given in the Report of the Medical Officer of the County of London for
1903 (Opp. p. 13), shows a rough correspondence between the flea and bug curves and some of these
notification curves. Having regard to the comparisons which have been made between the curves
of seasonal prevalence of flies and of diarrhoea, it becomes a matter of interest to examine these rough
correspondences a little more closely with a view to learning whether they throw any light upon the
general question of possible insect carriers of infection.
In the cases of scarlet fever and diphtheria, there are certain facts which suggest the desirability
of keeping an open mind as to whether the last word has been said concerning the mode of
spread of infection. For example—the special incidence upon children, and particularly upon children
in schools. The evidence as to fomites and the alleged clinging of infection to houses or rooms, or
in schools to particular departments or even classrooms.† Furthermore, mention may be made of
the fact that scarlet fever rarely spreads from an infected to an uninfected child in the ward of a
well-managed hospital, but such spread does occur ("return cases") after children are sent back to
their homes.‡ The possibility cannot, of course, be absolutely excluded that a biting insect has
played a part in transmitting infection from case to case in some instances, and that in the absence of
such intermediary, infection has not been transmitted.
In the year 1909 the London scarlet fever and diphtheria curves, it may be said at once,
were quite atypical. A considerable milk outbreak of scarlet fever occurred in June and July, and
disturbed the ordinary development of the rise usually observed in those months. Apparently, however,
the true autumnal maximum for scarlet fever occurred in the thirty-eighth and that for diphtheria
in the thirty-ninth week; while the maxima for both the biting insect curves occurred in the thirtyfifth
week. There was thus an interval of three or four weeks between the attainment of the maxima
in the latter instances and in the former. In the case of flies and diarrhoea, no such interval is, as
a rule, observed, the curves are practically superimposed one upon another. The bearing of this
fact upon the hypothesis of fly causation of diarrhoea has been already considered, and it has been
pointed out that there is, in the absence of any such interval, little, if any, time available for dissemination
of infection, incubation, etc. It must be remembered, however, in this connection, that
there is no need for time for development of an organism in the body of the fly. The suggestion has
never been made that the hypothetical organism of diarrhoea passes a phase of its existence within
the fly in the manner demonstrated for the malaria organism within the mosquito. If the fly merely
acts as a carrier there is, at any rate, no question of allowing time for such development
It will be interesting to learn whether or no the figures for future years confirm those of
last year, in respect of showing an interval between the time of occurrence of the maxima for fleas
(or bugs) and the maxima for scarlet fever and diphtheria. Obviously, at the present time, no more
can be said than that the subject is one deserving of further study. The difficulties encountered in
constructing a seasonal curve for fleas are considerable, but they should be surmounted, if it be
only with a view to throwing further light on the study of seasonal curves of disease in relation to
corresponding curves for possible carriers of infection.
* For example, Dr. Copeman, F.R.S., in a recent report on Enteric fever at Workington, raised question as
to whether, in certain instances, direct inoculation by means of flea-bites had occurred.
† Dr. Niven has referred (Annual Reports, 1897-1901) to evidence of "the tenacity of the disease as regard
particular departments." He says, "It may go on for a year or more in a department, attacking a case in May,
another in June, another in July, and so on." Again, he observes, " The history of scarelet fever in schools seems
to imply a low power of aerial transmission."
‡ Mr. T. W. Thompson (Vol. XV. Epidem. Soc. Trans.), in discussing the " return ease " problem, enumerated
possible causes of the differing incidence on one as compared with another class of household. He referred to the
influence of school attendance, social circumstances, etc., but concluded. " some more obscure factors are at work,
factors perhaps closely bound up with the natural history of scarlet fever."
W. H. Hamer,
Medical Officer (General Purposes).