Nineteenth-century India was not an easy place to live in. There were major famines brought on every few years by drought-induced crop failures. Millions died from starvation or disease – or, in many cases, both. In the northern and central hinterland, thousands fell victim to a crippling disease, a form of paraplegia called lathyrism that paralysed their legs. In village after village, there could be seen shambling men, some stumbling along on bamboo crutches and some reduced to crawling. The culprit for the malady was said to be a seemingly innocuous food item – a semi-wild vetch popular among the...