Other viruses that can cause colds include coronavirus, respiratory syncytial virus, influenza and parainfluenza. Colds cause a lot of people to stay home. The CDC says 22 million school days are lost each year in the U.S. because of them. Some estimates say that Americans have 1 billion colds a year. For more detail, see Common Cold Causes. How a Common Cold Starts. You can catch it from another person who is infected with the virus. This can happen by direct physical contact with someone who has a cold, or by touching a surface contaminated with their germs -- like a computer keyboard, doorknob or spoon --- and then touching your nose or mouth.
The hypocaust system. The hypocaust system (hypocaustum in Latin) was a heating system used in (wealthy) Roman homes and Roman baths, and the closest thing to central heating today. The hypocaust was a system that circulated hot air under the floor and surrounding walls. Hypocaust construction
Roman central heating worked slightly differently, but the goal was the same. A ground level furnace was used to create hot air which circulated beneath a thin floor raised up on pillars of tiles â this system was called a hypocaust. Not only was this central heating, it was underfloor heating! Smoke and fumes from the furnace were channelled off via flues so as not to pollute the heated space above. The same method was used to heat the waters in bath houses (yes, the Romans gave us hot baths too). Concrete. Opus caementicium (Roman concrete) was made from quicklime, pozzolana and an aggregate of pumice.