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1929
36
not grow on any media at temperatures under 25° Centigrade
(about 77° Fahrenheit): it dies at a temperature of 23° Centigrade.
Special media have to be prepared for its growth and extra precautions
are necessary in order to obtain specimens f it. When
diphtheria patients, for instance, are swabbed, the nose or throat
is swabbed and the swab sent to the laboratory and there transferred
to the growth media. But in the search for the meningo-coccus,
the swabs must be taken from the back of the nose, and transferred
immediately to the growth media. If the swabs were taken to the
laboratory and transferred in the ordinary way, the drying and
cooling would be sufficient to kill the germ and no growth would
result.
The germ is found in the cerebro-spinal fluid and brain
coverings of persons suffering from the disease, but only occasionally
from the secretions of the nose and throat. This probably
explains why the infection very rarely takes place directly from
patient to patient. The grerms are very rarely isolated from the
naso-pharynx of those suffering from the disease. Even in carefully
studied outbreaks it is exceptional for infection of a patient
to be ascribable to any known case of cerebro-spinal fever. In
other words, direct association with the sick is neither a necessary
nor even a common factor in contracting cerebro spinal fever. The
spread of the infection usually takes place through the medium of
a third person or ' carrier ". The germ is very frequently found
in the nose and throat of "carriers," that is, persons who harbour
the germs, but who are suffering from no symptoms. There is
evidence to the effect that meningococci are to be found in the nasopharynx
of persons living in areas in which there has been no
outbreak or epidemic of cerebro-spinal fever. In outbreaks of the
disease where contacts have been swabbed the percentage of
"carriers" may be very high. Possibly nearly 3°/o of the population
may be harbouring the germs, though in the majority of the
cases the germs are quite harmless. Different figures are given
where extensive swabbing has been done, and the percentages vary
from two to ten per cent.
So long as the germs remain in the nose and naso-pharynx,
they give rise to no symptoms or at any rate to nothing more
serious than a slight catarrh. It is only when the organisms gain
entrance to the brain cavity that symptoms of meningitis occur.
It is not known what the conditions are which determine the migration
of the organisms from the naso-pharynx into the brain cavity.
It is surmised that some changes occur in the mucous membrane
which enable the organisms to penetrate the protective barrier.
If a person does not harbour the g-erms, but comes in contact with
a "carrier", a susceptibility to the disease would render the
person liable to contract the disease. The immunity which the