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21
infections. The tendency later was to attribute an infectious
illness as due only to invasion by the peccant organisms. The
swing of the pendulum probably went too far, as there is no doubt
about the influence of factors in affecting the susceptibility of the
host. In the absence of the virulent organisms, the specific
disease does not arise; but something more than the mere presence
of the organism is required to determine the onset of disease,
and constitutional factors can influence for longer or shorter
periods of time the degree of susceptibility or immunity of the
host. While therefore, it is possible to ascribe within certain
limits the ordinary period of incubation of a disease, in certain
circumstances there may arise a combination of factors which can
result in the interval of time between the reception of the invading
organisms by the host and the onset of the illness being outside the
ordinary maximum limits of the incubation period.
The large number of secondary cases of scarlet fever cannot
therefore be taken as an indication that the present steps taken
in dealing with infected articles in the home are any less efficient
than those previously carried out. Actually it is probable that
they are far more effective, in that when terminal fumigation was
practised, there would be a tendency on the part of many to
consider that the procedure afforded complete protection and so
would render the householders lax in carrying out the most necessary
steps in regard to the disinfection of those articles more likely to
be contaminated; whereas now, in the absence of fumigation,
they are made to realise that those steps are essential and this
should result in their being much more efficiently carried out.
The 10 secondary cases of diphtheria could also be attributed
direct personal infection. Two were secondary to a missed
nasal case; in another four the onset of the secondary was prior
to the removal to hospital of the primary case, and in the case of
a further three, the onset of the secondary was within 24 hours
after the removal of the primary infecting case. The remaining
case was one whose alleged onset was the fourth day after the
removal of the primary case. As the incubation period of this
disease is given as 2 to 10 days, it can be accepted that this was
another direct personal infection. In none of these cases then is it
necessary to assume infection by means other than direct from
the patient, and they afforded no proof of the infectiousness of
inanimate articles.
The relation of secondary infection to removal to hospital
of the primary case is considered under the heading of scarlet
fever; also consideration is there given to the return eases. One
of the alleged reasons for these cases is the bringing out on the