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86
ringwcrm
and Favus.
public elementary schools in 1919, as compared with 2,639 during the preceding year. The following
table shows the number of cases which have occurred, and the number of cures effected annually during
the past nine years.
Cases outstanding
Fresh cases. Cured cases. at the end of the year.
1911 6,214 5,872 2,458
1912 5,311 5,131 2,204
1913 5,573 5,257 2,277
1914 4,449 5,902 1,638
1915 3,747 3,928 1,334
1916 3,115 3,081 1,232
1917 2,814 2,964 992
1918 2,639 2,555 979
1919 3,447 3,103 1,259
The number of hair specimens submitted by school nurses and assistant medical officers for
microscopical examination was 2,566, of which 1,342 were found to contain ringworm fungus and seven
showed the presence of favus. The remainder showed negative results or were referred for further
examination. Only seven fresh cases of favus were reported during the year.
In residential special and industrial schools and places of detention, the standard of health so
far as infectious diseases, such as scarlet fever, diphtheria, measles, etc., is concerned, has been satisfactory.
On occasions when such ailments have been introduced preventive methods have been taken
and outbreaks have been averted.
The parts
played respectively
by
changes in
the organism, and by
changes in
the environment
in connection
with
measles
prevalences.
In last years report the subject of variation and persistency of type in epidemic disease was
illustrated by study of the behaviour of tuberculosis, scarlet fever and influenza. Thus, as regards
tuberculosis (Annual Report, 1918, Part I., pp. 6—8) reference was made to the contention of Dr.
Brownlee, that the existence of one kind of age distribution of mortality from phthisis in Cornwall,
and of other kinds in Ireland and in London, suggests that different strains of tubercle bacilli must
be operating. This strain hypothesis is likely to prove hard of acceptance, at any rate until the objection
has been met that the phenomena can be much more simply and satisfactorily explained as resulting
from migration and movement of population; and if this latter view be correct tuberculosis must be
regarded as a disease of notably persistent type. In contrast to this, however, there has undoubtedly
been variation in type of scarlet fever (loc. cit., Part II., pp. 44—49) and still more in influenza; in
last year's special examination of the history of influenza (loc. cit., Appendix, Report on Influenza) it
was made clear that the great pandemic prevalences are apt to be both preceded and followed by remarkable
associated outbreaks, and that these admit of being explained as being the outcome of change in
the type of the epidemic disease.
The general trend of opinion now appears to be in the direction of recognising that variation
of type in disease depends on environment (including in this term the several degrees of immunisation
of affected populations) as well as upon changes in disease germs; and, further, as regards the latter,
it is clear that the searchlight of enquiry must not merely be focused upon the bacteria, which have
hitherto formed the main objects of interest, but must be even more particularly directed to study of
cyclical changes in the life history of far more elusive organisms, the laboratory teaching with regard
to which still leaves much to be desired. It is interesting, however, to find that Dr. Brownlee is still
disposed to concentrate his attention almost exclusively upon continuous variation in the germs, which
he regards as being governed by physico-chemical laws, the action of which can be studied, independently
of the effects of environment : and he now claims that his strain hypothesis has important applications
even in measles and smallpox. Here it should, at once, be pointed out that the remarkably stable
measles and smallpox are poles apart from the protean influenza ; furthermore, in the case of the unstable
influenza itself, the changes which the epidemiological facts demand are, in the main, changes of a discontinuous rather than of a continuous sort. However, subject to these preliminary objections as
■egards measles, smallpox and influenza, Dr. Brownlee's general hypothesis, his attempt to explain
periodicity as due to continuous variation in disease germs, needs, of course, to be very carefully
examined.
He himself indicated the scope of the field of enquiry, two years ago, in the following statement : " Of periodicities in infectious diseases two explanations are possible. On one hypothesis the
periodicity may be due to causes depending on the variation of infecting power of the causal organism,
multiplicity of period depending on different strains of the organism having somewhat different life
properties; on the other, the varying local conditions in different parts of a city might be sufficient
to account for the phenomena found, as the method of the spread of a disease and the number of
persons infected in any epidemic must depend to some extent on the number of susceptible persons, on
the density of population, on the season of the year, and on other similar causes. These two explanations
have very different bases. In the one case the infecting organism is the main factor. In the second,
the conditions of the population."
The field epidemiologist will certainly assume that both explanations must be reckoned with.
Dr. Brownlee, however, notes that from a mathematical point of view " the periodicities can be explained "
on either of the hypotheses separately. He says : " Of course, these theories are not mutually exclusive ;
the point to be determined is their relative importance. My opinion is strongly in favour of the first
hypothesis."
Presumably the relative importance in question varies according to the type of epidemic disease
under consideration, and the particular instance now to be closely examined is that of one of the most
stable of epidemic diseases—measles—and all the evidence thus points to the conclusion that the second