d necessary
share of the risk. That has always been the case. We now know that the
medieval horror of leprosy was out of all proportion to the danger
of infection, and was accompanied by apparent blindness to the
infectiousness of smallpox, which has since been worked up by our
disease terrorists into the position formerly held by leprosy. But the
scare of infection, though it sets even doctors talking as if the only
really scientific thing to do with a fever patient is to throw him into
the nearest ditch and pump carbolic acid on him from a safe distance
until he is ready to be cremated on the spot, has led to much greater
care and cleanliness. And the net result has been a series of victories
over disease.

Now let us suppose that in the early nineteenth century somebody had
come forward with a theory that typhus fever always begins in the
top joint of the little finger; and that if this joint be amputated
immediately after birth, typhus fever will disappear. Had such a
suggestion been adopted, the theory would have been triumphantly
confirmed; for as a matter of fact, typhus fever has disappeared. On
the other hand cancer and madness have increased (statistically) to
an appalling extent. The opponents of the little finger theory would
therefore be pretty sure to allege that the amputations were spreading
cancer and lunacy. The vaccination controversy is full of such
contentions. So is the controversy as to the docking of horses' tails
and the cropping of dogs' ears. So is the less widely known controversy
as to circumcision and the declaring certain kinds of flesh unclean by
the Jews. To advertize any remedy or operation, you have only to pick
out all the most reassuring advances made by civilization, and boldly
present the two in the relation of cause and effect: the public will
swallow the fallacy without a wry face. It has no idea of the need for
what is called a control experiment. In Shakespear's time and for long
after it, mummy was a favorite medicament. You took a pinch of the dust
of a dead Egyptian in a pint of the hottest water you could bear to
drink; and it did you a great deal of good. This, you thought, proved
what a sovereign healer mummy was. But if you had tried the control
experiment of taking the hot water without the mummy, you might have
found the effect exactly the same, and that any hot drink would have
done as well.

BIOMETRIKA

Another difficulty about statistics is the technical d