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154
1913]
How the Virus Gains Access to the Human Body.—The most probable
portals are the mouth, throat, and the respiratory and alimentary tracts, from
which the virus, having first pierced the mucous membrane, passes into the
lymphatics, which convey it to the spinal cord and nervous centres. Romer,
in discussing this point, says: " Many things point to the virus remaining for
a long time in the mucous membrane of the mouth and throat of infected
individuals. One might think of the infection by the saliva in speaking,
coughing, sneezing, or in more direct contact. Unfortunately, there is no
proof that the virus is contained in the saliva." And he goes on to say:
"Considering how little we really know about the pathogenesis of the disease,
any attempt to explain how infection occurs under the conditions of an
epidemic must be fraught with almost insuperable difficulties." Since Romer
penned these remarks, Kling, Wernsdett and Petterson have succeeded in
producing the disease in monkeys by using saliva and intestinal contents,
while Newstadter and Thro have done the same thing by the use of dust from
the sick room. Nevertheless, a difficulty arises as to how epidemics spread,
which is only, after all, a similar one to that which has long since arisen as
to epidemics of Scarlet Fever.
How the Disease is Spread.—It is generally agreed that the chief method
of transmission of the disease is the direct one; that is to say, from human
being to human being, although the "carrier" must not necessarily be the
sick person. This was Wickman's theory of transmission by human contacts,
which is brought about by typical cases, but especially by the abortive forms
which usually form the majority, and which may easily pass unrecognised,
and, consequently unisolated.
Kling and Livaditi found that the hypothesis of the transmission of
disease by means of water, milk, dust, flies, bugs and mosquitoes was not
confirmed either by experimental results or epidemiological data; that patients
are infectious during the incubation period; and that man appears to be the
sole depository of the virus.
Persons Whom the Disease Attacks. Children, as already stated, are
most frequently attacked, although adults are sometimes sufferers. Thus out
of 153 cases in Cornwall and Devonshire reported on by Reece, 121, or 79
per cent., were under ten years old, and that all, with one exception, were
under forty. The following statement, prepared by the Medical Officer
of Health from his figures, gives the percentage of cases of four decades
of life: —