Occasions when it is socially acceptable to inject liquids fall into two broad types: first, when the liquid is supposed to cure an illness (or at least to dull the pain) and, second, when the liquid is supposed to immunise against an illness ever taking hold. Having been forced to inject liquidity into sickly money markets over the summer, central banks are now considering what kind of injections will ward off further financial disease.

Strain in the money markets has got worse in the past couple of weeks. In the US, UK and eurozone, the rates banks are charging each other to borrow for three months are well above central bank base rates, which is especially unusual because the market expects US and UK rates to fall. In response, the European Central Bank is making weekly liquidity injections, and the US Federal Reserve has announced it will lend a larger-than-usual $8bn to banks, against the security of their bond holdings, over the year end.