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26
be prevented from mixing with healthy persons, I now give
a list of these diseases and the time during which it is probable
that the disease may be communicated to others:—
Small-pox 8 weeks from appearance of rash.
Modified do 5 weeks ditto
Chicken-pox 18 days ditto
Measles 4 weeks ditto
German Measles 2 weeks ditto
Scarlet Fever 7 weeks ditto
Diphtheria 4 weeks from first illness
Erysipelas (not from wounds)—5 weeks
Typhoid Fever—4 weeks
Mumps—3 weeks from date of swelling
Some of these diseases, viz., small-pox and measles, are infectious
before the rash comes out, and whooping cough before the
"whoop" is heard, so that it is often very difficult to ascertain
when the disease was caught. This is all the more difficult as
the period of incubation, i.e., the time that occurs between the
date of infection and the appearance of the rash, varies. In smallpox
this is said to range between 8 and 20 days, the usual time
being from 12 to 14 days, and we may fairly allow the same
time for measles and whooping cough. The time during which
a small-pox patient remains infectious varies somewhat in
different cases, and, as shown above, whether or not the patient
has been vaccinated or had a former attack, that is to say, has
the disease in a "modified" form. At any rate infection has
not ceased whilst there is any crust on the body, and I believe
it still remains in the body as long as thin scales are continued
to be found on the places where the pustules have been, and
the same may be said of scarlet fever so far as the peeling
of the skin is concerned.