In 1937, US physician Conrad Elvehjem made a sensational discovery: it was vitamin PP (Pellagra Preventive), the lack of which was responsible for pellagra, a terrible disease that afflicted the rural population of northern Italy, particularly the Veneto region, and was the main cause of death. This was an important discovery because it brought to light that the main food in the peasants' diet, polenta, was associated with the onset of this disease, as polenta was almost devoid of vitamin PP. Basically, polenta was a typical country dish, so wheat was used in the city to make bread, as it was more valuable than other cereal varieties. Moreover, it was a way of preparing food: since ancient times "the simplest and cheapest way to consume cereals was to reduce them to flour and cook them in water to make a soup"; in essence, "the various non-corn polenta we find around Italy today are often survivals from the past". A crucial innovation was corn, imported to Europe after the discovery of America, but only used on a large scale from the 18th century onwards to cope with a substantial increase in population: in fact, the increase in population led to a search for products that guaranteed the largest harvest for the same amount of cultivated area - the only one that was never abandoned was wheat. As Alberto Grandi and Daniele Soffiati write, "around 1870, Veneto peasants ate two or three kilos of polenta a day, even spending 60 per cent of their income on corn flour". When corn polenta was no longer enough to feed the peasant population, emigration to the United States - at first from the Veneto region - became the only solution, also because it allowed the food pressure to be eased and provided additional income to the families of Italian emigrants by sending "remittances".