Angela Horner, age 13, of Ashford, Wash., for her question:

HOW DOES THE COW'S STOMACH WORK?

In the Mediterranean area many people drink goat's milk while in large sections of Asia mare's milk is used

extensively. Egyptians and Arabs drink camel milk. Eskimos and Laplanders drink the milk of reindeer. Here in North America, cow's milk is an important item found on almost every menu.

There's a popular question that asks: How can a brown cow eat green grass and produce white milk? The answer is actually rather simple because the cow has a four part stomach that helps to turn grass and hay into nourishing milk.

Domestic milk cows have rather small heads but large jaws and teeth which are used for chewing grass and hay. There are no teeth at the end of the upper jaw but instead this part of the jaw is covered with a tough membrane like a pad. The incisor teeth at the end of the lower jaw press against this pad so that the cow pulls off, rather than cuts off, the hay and grass it eats while grazing.

When a cow is standing or lying under a tree and is munching, it is said to be chewing its cud. Food that was swallowed when the cow was grazing is forced back into its mouth in small balls or "cuds. " After chewing the cud, the cow swallows the food again and it passes to the next chamber of the stomach. The process is repeated a number of times.

This rechewing of food by the cow is known as rumination and it takes place only when the cow is resting, not while it is grazing.

Cattle have been useful to man for many hundred years. It is said that they descended from the prehistoric ox which is closely related to the buffalo, bison and yak. When Columbus came to America on his second trip from Spain in 1493, he brought with him the continent's first cattle.

Farmers have improved cattle since the middle of the 18th century by selective and scientific breeding of the cow. The milk giving features were stressed so that today's dairy cow is truly a master in the art of producing milk.

Louis Pasteur, the French scientist, discovered harmful bacteria in milk could be eliminated by heating the milk to a certain temperature and then, after ashort time, cooling it rapidly. Now most milk is given this treatment  it's called pasteurization  and it is then quickly sealed into clean bottles or cartons so new germs cannot get in.