What is a heifer cow? A heifer is a mature female cow that has not calved, or given birth to a calf, yet. As soon as a heifer gives birth, she becomes a cow. A cow refers to a female of any age that has given birth.
When most people think about gas masks or respirators, what they usually envision is a tight-fitting plastic or rubber face mask with some sort of filter cartridge. The mask covers the nose and mouth. These are called half-mask air-purifying respirators.
Fire fighters came to rely upon the gas mask in rescue attempts, and the invention helped save thousands from chlorine gas and other noxious fumes during World War I. Next Morgan created the three-way traffic signal, a device responsible for saving thousands of lives over the years.