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complexes, and, again, the association of cerebro-spinal fever in particular families with cases of
influenza, catarrh, etc., and not, as a rule, with other cases of cerebro-spinal fever.
In this connection it may be pointed out that study of the extent to which development of
cerebro-spinal fever occurs among the civil population in those who have been associated with soldiers,
or those whose homes have been visited by soldiers, affords an interesting " control experiment," for
testing the significance of the relationship of cerebro-spinal fever, and influenza. Out of 462 returns,
relating to the epidemic period January to May, 1915, more than 20 per cent. give a history of influenza
or catarrh, and nearly 40 per cent. give either such a history or a history of contact with sufferers from
influenza or catarrh. The percentage of returns relating to civilians in which association with soldiers
is recorded is much lower than this. A priori it might perhaps have been expected, in view of the
respective extents, of the prevalences of influenza and of cerebro-spinal fever, and of the intercourse
between soldiers and civilians, during the months in question, that the first-named kind of association
would have been considerably less frequent than the second. As a matter of fact, however, that
first-named was actually recorded in nearly 40 per cent, and the second in only about 17 per cent, of

It should be added that in the first of the three periods there were more soldiers quartered in
London than in the other periods. While in the first period the extent of association between
cerebro-spinal fever and contact with soldiers was 17 per cent., as against 40 per cent. for that
between cerebro-spinal fever and influenza or catarrh, in the second period the corresponding figures
were 14 per cent. and 10 per cent., and in the third 13 per cent, and 25 per cent.
The very careful report of the Advisory Committee sets out concisely the main difficulties so
far as the meningococcus is concerned. The Committee was confronted with the problem presented
by an organism which, to begin with, is sometimes difficult to find in the cerebro-spinal fluid. ..."Most
of the reporters admit negative results, and they sometimes amounted to 25 per cent of the total cases
examined" (p. 28); again, "the great majority of the reporters complain of the unsatisfactory resvdts
of the method for determining the presence of the meningococcus in the nasopharynx" "The
work is tedious and beset with pitfalls, while its results were often found ambiguous" (p. 33); then,
thirdly, in the pharynx of actual sufferers "the meningococcus has been much less commonly found
during the attack than might have been expected" (p. 29). These difficulties, in conjunction with
the freedom from any ill resu'ts in the case of carriers, with the non-infectivity of the actual subjects
of the disease, and with the common occurrence of the carrier state in non-contacts, make it necessary
for the bacteriologist to fall back upon an hypothesis described as one of a "saprophytic epidemic"
of the meningococcus "in the throats of the population at large." Major Gordon, by means of the
agglutinin absorption test divided meningococci from the meninges into "types," and when he. "applied
his test to pharyngeal strains he found that only a portion of these were to be included in his types ;
it is possible that the residue were non-epidemic and less harmful races." Hence arises the theory of
"immunological races" and "epidemic strains" of the meningococcus—the organism, it is declared,
is "essentially a saprophyte, though with potentialities of parasitism, divided up, as mosb bacteriological
species probably are, into a number, perhaps a large number, of races distinguished by their immunological
reactions. At ordinary times, when cerebro-spinal fever is not epidemic, the saprophytic spread
of these races is attended only by the development here and there of sporadic cases of declared disease
in the most susceptible elements of the population, the posterior basic meningitis of infants. But from
time to time, and hitherto very rarely in this country, individual races attain a greater virulence, and
their saprophytic spread is attended not only by a larger number of cases of meningitis but by the
attack of young adults, who, in ordinary circumstances, are immune. ... In any epidemic there will
occur a saprophytic spread of the epidemic strains, side by side with the domestic and relatively harmless
strains indigenous to the locality, so that there are carriers of either, indistinguishable except by serological
means." It is a matter for sincere congratulation, to all who may possibly be regarded as coming
under suspicion, to find it suggested "that only those carriers need be isolated who bear epidemic
strains."
The conceptions above outlined are, it is pointed out, to be regarded as representing a "working
hypothesis only"; there can be no "pretence of finality" . . . "it seems doubtful whether these
immunological races will be found quite sharply separable"... they are defined "by methods the