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104
Were school attendance a potent factor in the production of
the Schick negative state, there would not be this difference
exhibited amongst the two sets of school children.
Moreover, in the results of Schick tests at various ages, as
already pointed out, there is no marked change in the curve showing
the increase in the percentage of immunes at increasing age, at the
age of entry into school. Some factor operates in turning susceptibles
into immunes from the youngest ages onwards, and this
factor appeal's to be no more, or no less potent, at school age than
up to the time of admission into school.
The ordinary child is exposed to infection from many sources,
some more dangerous than others. Playing with companions in the
streets or pleasure grounds, even though contact is very close, for
short periods only, should not result in much risk. Considering
all the factors involved in the " velocity of infection," including
the massiveness of the dose and the time for which it is delivered,
a well diluted infection in the open air will not be a very potent
factor. The matter is rather different, of course, where " out-ofdoors
" consists of a cooped-in back alley. Such places can be as
poorly ventilated and as heavily infected as a stuffy room. Exposure
to contact with cases in cinemas, shops, buses and trams, owing
to the close contact with massive infection over a period of time,
is more likely to result in an actual case of illness.
It seems that the place where, ordinarily, a child is brought
into surroundings in which the circumstances are most in favour of
the conveyance to him of organisms of infection, cither in lethal or
sub-infective doses, is his own home. Here the influences are
operative towards infection, more than in any other place. The
infecting person, cither relative or neighbour, is in close contact
for a period of time, often in a place suffering from lack of ventilation.
Contact in the room results possibly in infection, more often
in a subliminal dose. Contact in the bedroom results more
frequently in infection.
It is suggested that, in general, the gradual increase in relative
immunity to the ordinary infectious diseases acquired with
increasing age, is due to subliminal infections which are mostly
received by the children, in their homes, from healthy carriers.
In this district, owing to the relatively smaller proportion of
farriers compared with the number of susccptibles, the children c.o
not receive these small doses to the same extent as formerly,
and so far from acquiring, by repeated small infections, their
nnmunity—in certain cases they might even lose that amount of
resistance they had previously acquired. This loss of resistance