How This Text Is Built

How a Vaccine Teaches the Body

Your immune system learns. Meet a disease once and, if you survive it, you are usually protected afterwards. A vaccine gives the lesson without the disease. The method is old. In eighteenth-century Britain, milkmaids were known not to catch smallpox. Edward Jenner reasoned that the cowpox they caught from cattle was protecting them, and in 1796 he tested it on a boy — a procedure no ethics committee would permit now. A modern vaccine shows the immune system a harmless piece of a pathogen: a killed virus, a weakened one, or a single protein from its surface. The body makes antibodies against that piece, and keeps the recipe. Because the recipe is kept, the real pathogen is met by a defence already in place. There is a second effect. If enough people are immune, the pathogen cannot find a chain of hosts, so those who cannot be vaccinated are protected too. That effect fails below a threshold, which is why coverage rather than availability is what matters.

Two Plants, Two Histories

Tea and coffee are both leaves or seeds steeped in hot water, and both became national habits. How they got there could hardly be more different. Tea came to Britain through a monopoly. The East India Company controlled the trade for nearly two centuries, and the government taxed it so heavily that by the 1770s most tea drunk in Britain had been smuggled. When the tax was cut in 1784, smuggling collapsed almost overnight. Coffee spread through places rather than trade. The coffee house arrived in Britain in the 1650s and became somewhere to read newspapers and argue. Lloyd's of London and the London Stock Exchange both began in one. Tea won the home; coffee won the meeting. Neither plant grows in Britain. Both habits are entirely imported, and both are now so ordinary that they are thought of as native.