The theory gradually disappeared. Doctors began to wear surgical masks from 1897. Masks are not designed to filter viruses or bacteria in the air. And this is not the focus of surgical mask design today. Doctors wear surgical masks mainly to prevent droplets produced by sneezing or coughing from falling on patients' wounds during surgery. 19 10 autumn, a plague broke out in Manchuria. The death rate of this plague is as high as 100%, and the infected person will die within 24 to 48 hours. China and Russia launched a scientific arms race to find the source of plague and stop its spread. The Qing government hired a doctor named Lian Dewu to lead this work. Wu was born in and studied medicine in Cambridge. He is still young and unknown. After an autopsy on a victim, Wu determined that the plague was not spread by fleas, but by air. He then expanded the use of surgical masks at that time and improved them to cover the face more firmly. His invention is a breakthrough, but some colleagues doubt it. A French doctor denied that the plague spread through the air. He went to the hospital to deal with the plague without wearing a mask and died of the plague two days later. Wu's mask quickly became popular. 19 18 masks used in the Spanish flu epidemic are well known. The popular N95 mask is its derivative.