Tobacco was introduced into China at the beginning of the Ming Dynasty. At first, people thought that smoking could cure a lot of diseases, and could do good to people's health. However, Chinese doctors discovered that smoking would do great harm to people's health through animal experiments and clinical observation. They found that the poisonous materials in smoking include virulent fire - evil, tar, and some other invisible materials harmful to spirit of the body. Doctors also discovered that smoking had a great effect on people's lungs, causing damage to multiple organs and eventually death. Hence, trading on tobacco was banned officially in the Ming dynasty. Propaganda movements against smoking during the Qing Dynasty were gradually developed among the people.