To all these blunders and ignorances doctors are no less subject than
the rest of us. They are not trained in the use of evidence, nor
in biometrics, nor in the psychology of human credulity, nor in the
incidence of economic pressure. Further, they must believe, on the
whole, what their patients believe, just as they must wear the sort of
hat their patients wear. The doctor may lay down the law despotically
enough to the patient at points where the patient's mind is simply
blank; but when the patient has a prejudice the doctor must either keep
it in countenance or lose his patient. If people are persuaded that
night air is dangerous to health and that fresh air makes them catch
cold it will not be possible for a doctor to make his living in private
practice if he prescribes ventilation. We have to go back no further
than the days of The Pickwick Papers to find ourselves in a world where
people slept in four-post beds with curtains drawn closely round to
exclude as much air as possible. Had Mr. Pickwick's doctor told him that
he would be much healthier if he slept on a camp bed by an open window,
Mr. Pickwick would have regarded him as a crank and called in another
doctor. Had he gone on to forbid Mr. Pickwick to drink brandy and water
whenever he felt chilly, and assured him that if he were deprived of
meat or salt for a whole year, he would not only not die, but would be
none the worse, Mr. Pickwick would have fled from his presence as from
that of a dangerous madman. And in these matters the doctor cannot cheat
his patient. If he has no faith in drugs or vaccination, and the patient
has, he can cheat him with colored water and pass his lancet through the
flame of a spirit lamp before scratching his arm. But he cannot make him
change his daily habits without knowing it.