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.
Inhaled minimal sedation. You breathe nitrous oxide -- otherwise known as laughing gas -- combined with oxygen through a mask that's placed over your nose. The gas helps you relax. Your dentist can control the amount of sedation you receive, and the gas tends to wear off quickly.