Working in East Africa, I used to give an afternoon a week to a remote Catholic mission down a bumpy laterite road. It was run by a Swiss nun, aged about seventy, and, astonishingly, it was as spotlessly clean as the most expensive Helvetian clinic. The nun, who had devoted her life to work in Africa, was surrounded by an aura of inviolability: in her case, cleanliness really was next to godliness.

Among my duties was that of giving a three-month contraceptive injection to mothers who already had ten or more children as well as heart disease that would render fatal the bearing of another child. The mothers had come long distances, and their husbands knew nothing of why they had come, for they would not have approved if they had known. The nun would absent herself while I gave the injection (though it was the mission that provided it); in the room in which I gave it there was a large photographic portrait of the Pope.

No...