OCR Text |
Show Ever-Growing Teeth. Certain animals have teeth which grow all their lives. The rat and the squirrel are examples of this. Human teeth are developed from pulps, which are absorbed and disappear after the teeth are grown; but in the case of a rat the tooth pulp is perpetual, and is continually secreting material by which it gains length. Therefore the animal is obliged to gnaw all the time to keep the tooth down to its proper length. It is commonly believed that rats keep gnawing out of pure mis-cmef, mis-cmef, but such is not the case. |