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22
that when the disease attacks those who have not
been vaccinated, it is fatal to 37 per cent. of them,
or rather more than one in three; whereas in those
cases where vaccination has been performed, whether
properly or improperly, the mortality is only at the
rate of 6.8 per cent., or about one in fifteen. He
finds, moreover, that the protective power of vaccination
is directly proportional to the way in which it
has been performed ; for if it has been so done as to
leave upon the arm the well marked signs of the
operation, the mortality is only at the rate of 2.5
per cent., whereas in badly marked cases it is 8.8
per cent. And, by going still further with the
enquiry, he has ascertained that, when there are
four well marked cicatrices upon the arm, the mortality
is only 0.6 per cent.; when there are three,
it is 1.9 per cent.; when there are two, it is 4.7 per
cent.; when there is but one, it is 7.7 per cent.; and
when there are none apparent, although vaccination
is said to have been performed in infancy, the
mortality is at the rate of 23.6 per cent. of those
who are attacked with the disease; the mortality of
un-vaccinated being as high as 37 per cent. It would
seem, indeed, from his investigations, that vaccination
when properly performed is even more
protective of fatal consequences than a previous
attack of small-pox; for in the latter case the mortality
is as high as 19 percent. "Not a single