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column, was 43.9 for the first years of each quaternary period;
for the second, 20.3; for the third, only 11.9; for the fourth 23.9
per cent. The most cursory examination of this table shows, I
think conclusively, that the disease has been epidemic in certain
years in obedience to certain causes which permanently influence
its course. As I stated in my last report, this tendency to
periodical recurrence is no reason for relaxing our efforts to
diminish its spreading and intensity by proper sanitary precautions,
but on the contrary should spur us on to greater efforts in
the hope of ascertaining the causes which enable it to assume
this form. There is also another reason why we should
remember this tendency to become epidemic every fourth year,
viz: that vaccination should be most strenuously enforced in
the year before an epidemic is expected, so as to diminish the
number of those who would otherwise be susceptible to an attack.
It must not be supposed that I believe effective vaccination
to be a positive protection against an attack, because I do not,
but I consider it to afford at least as good a protection as an
attack of Small Pox would do. I had under my care, nearly
twenty years ago, a lad thirteen years of age who was deeply
pitted from a former attack of the disease, and who yet died
from the second, which assumed a confluent form. I have seen
numerous cases of second attacks of Small Pox, and one of a
third, and in nearly all, the progress of the malady was similar
to that which it takes after efficient vaccination. The chief
points to be attended to are, that the vaccine lymph is to be taken
not later than the morning of the eighth day after vaccination;
that there shall not be any intermixture of blood with the
lymph; that in primary vaccination not less than four punctures
or scratches be made; and that re-vaccination be performed as
soon as the person has done growing. When less than four