Mark Matarelli, age 11, of Peoria, I11., for his question:

WHAT ARE OUR BONES MADE OF?

Our bones which seem so hard and solid contain lots of water and empty space. The hard bony parts are made mostly from calcium, phosphorous and other minerals. The softer materials inside contain fats, blood and an assortment of complex proteins called collagens. The ingredients for these wondrous biochemicals, naturally, are extracted from the food we eat  and healthy bones depend upon a healthy, well balanced diet.

The human body, as we know, is supported by an internal skeleton. Its 206 large and small bones work with some 600 large and small muscles to move this or that from here to there. This neat bony structure is built and rebuilt from various organic and inorganic chemicals digested from the diet.

Although a big bone seems hard and strong, it is much lighter than one would expect. Actually, the solid bony material forms a sort of crusty shell, while the inside is made of porous and softer materials. About half the total weight is in crusty shell. This is made from calcium and phosphorous, sodium and fluoride and other inorganic minerals. The crust is lined with rather stiff porous material, where certain minerals are stored and exchanged with various parts of the body.

Inside a large bone there is a cavity which contains fatty substances, including red or white marrow. The yellow marrow is made mostly of fat. The red marrow teems with rich blood vessels. This soft substance contains the centers where, in some mysterious way, the new red cells are manufactured to replenish the blood. Possibly certain other blood cells also are manufactured in the red marrow inside the big bones.

Obviously the simple ingredients are in the bony shell. The internal cavities are composed of highly complex biochemicals made from just about all the numerous ingredients the body uses. Milk and dairy products supply calcium type materials for the bony crusts. But the busy tissues in the bone cavities require vitamins, minerals and countless other food elements.

Almost all the vitamins play some role in building and maintaining healthy bones. So do proteins, fats and various carbohydrates. Hence it is sensible to eat a well balanced diet, including a wide variety of different foods  just to make sure that the busy bones get the multitude of ingredients they need.