Viruses such as Covid-19 can be transmitted through common behavior, such as coughing, speaking, singing or sneezing. The masks are effective in blocking most of the droplets carrying the virus, even from close range. The experiment devised by the director of the clinical microbiology laboratory at the Providence Sacred Heart Medical Center in Spokane (Washington, USA) clearly demonstrates their filtering power. Richard Davis collected droplets from the mouth and throat after coughing, speaking, singing and sneezing. Then he observed the multiplication of the bacteria in 24 on the culture plates with or without a mask. In a second experiment he focused on distance. If the virus had been in place of the bacteria, the effectiveness of covering the nose and mouth as an anti-contagion measure would be clear.
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