The first modern respirator

During 1920, a plague broke out between a shared jurisdiction of China and Russia. The Chinese Imperial Court brought in a young doctor named Lien-teh Wu that determined that the plague was not spread by fleas but through the air. He expanded upon the surgery masks he'd seen in the West, and made it from gauze and cotton and added several layers of cloth to filter inhalations.

When the Spanish flu arrived in 1918, the mask was well-known among scientists and the public.