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.
An oxygen mask is attached to a plastic tube and covers your nose and mouth. It is usually held in place by an elastic strap that wraps around the back of your head. You can use an oxygen mask if you need a lot of oxygen. Your healthcare provider may tell you to use a nasal cannula during the day, and a mask at night. A mask may help if your nose is dry or stuffy. Transtracheal oxygen is given through a small, flexible catheter inserted into an opening in your trachea (windpipe).