On Immunity

When Voltaire wrote “On Inoculation,” the primary meaning of the English word inoculate was still to set a bud or scion, as apples are cultivated by grafting a stem from one tree onto the roots of another. There were many methods of inoculation, including the snuffing of dried and ground scabs up the nose or the sewing of an infected thread through the webbing between the thumb and finger, but in England it was often practiced by making a slit or flap in the skin into which infectious material was placed, like the slit in the bark of a tree that receives the young stem grafted to it. When the word inoculate was first used to describe variolation, it was a metaphor for grafting a disease, which would bear its own fruit, to the rootstock of the body

The princess of Wales, having also survived smallpox, arranged for variolation to be tested on prisoners condemned to die. The prisoners lived, immune to smallpox, and were freed for their trouble. The

Vaccination is a precursor to modern medicine, not the product of it. Its roots are in folk medicine, and its first practitioners were farmers. Milkmaids in eighteenth-century England had faces unblemished by smallpox. Nobody knew why, but anyone could see it was true. Nearly everyone in England at that time got smallpox and many of those who survived bore the scars of the disease on their faces. Folk knowledge held that if a milkmaid milked a cow blistered with cowpox and developed some blisters on her hands, she would not contract smallpox even while nursing victims of an epidemic.
By the end of the century, just as the waterwheels of the industrial revolution were beginning to turn the spindles in cotton mills, physicians were noting the effects of cowpox on milkmaids and anyone who milked cows. During a smallpox epidemic in 1774, a farmer who had himself already been infected with cowpox used a darning needle to drive pus from a cow into the arms of his wife and two small boys. The farmer’s neighbors were horrified. His wife’s arm became red and swollen and she fell ill before recovering fully, but the boys had mild reactions. They were exposed to smallpox many times over the course of their long lives, occasionally for the purpose of demonstrating their immunity, without ever contracting the disease.
Twenty years later, the country doctor Edward Jenner extracted pus from a blister on the hand of a milkmaid and