Summarise What You Heard

Canals and Railways

Between 1760 and 1830 Britain built about four thousand miles of canal. Within forty years of that, most of it was losing money. A canal boat carried thirty tons behind one horse, where a cart carried two. That was transformative for coal and stone, which are heavy, cheap and not in a hurry. But a canal cannot climb without locks, cannot be built where there is no water, and freezes. A boat averaged three miles an hour. The railways did not beat canals on cost per ton at first. They beat them on speed, on reliability, and on where they could go — a railway can cross a watershed a canal cannot. Many canal companies were bought by railway companies, sometimes specifically in order to close them. By 1900 most of the network carried nothing. Some of it is now used more than it ever was, by people on holiday.

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.