Karl Neumann, age 14, of Marion, Ohio, for his question:
WHAT DOES BONE MARROW DO?
The laxger bones of the body are hollow and the space inside is occupied by an important living tissue called the marrow. Bone marrow may be either yellow or red. The yellow bone marrow is mostly fat, while the red bone marrow is a network of blood vessels, connective tissue and blood forming cells.
The yellow marrow is found at the distal end of long bones, toward the extremity. The yellow marrow is a storehouse of energy for the body, since in emergencies each gram of fat will yield from 9.2 to 9.4 kilogram calories of heat.
The marrow in the middle and at the proximal end (away from the extremity) is generally red. This is an extremely busy tissue since the combined activity of the red marrow of all bones of the body must produce about 10 trillion red blood cells each month.
The red marrow is especially sensitive to poisons and susceptible to infection. For this reason a microscopic examination of samples of the bone marrow from the sternum, for example, often gives valuable diagnostic information.
The area inside a bone is called the medullary cavity. The latin for "marrow" is medulla (the opposite of "cortex" which is the word for "bark" or "rind").
To the ancients, any tissue inside a bone was marrow, or medulla, and since the spinal cord lies inside a body canal (the vertebral canal) it was called the "medulla spinalis." This is still the international term for spinal cord. The upper extension of the medulla spina is in the brain is therefore logically called the medulla oblongata.
The Greek for "marrow" is "myelos." Myelitis means inflammation of either the bone marow or the spinal cord. To avoid ambiguity, one may speak either of ostemyelitis (inflammation of the bone marrow) or poliomyelitis (inflammation of the gray matter of the spinal cord.)
Bone marrow accounts for from 2 to 5 percent of the body weight of a person.
Bone consists of a chemical mixture of inorganic salt (65 to 70 percent) and various organic substances (30 to 35 percent) and is both hard and elastic. It's hardness is derived from inorganic constituents, principally calcium phosphate and calcium carbonate, while its elasticity is derived from organic substances such as gelatin and collagen.
Internal tubular structures called Haversian canals contain nerve tissues. and blood vessels that provide bones with organic nourishment. Surrounding these canals is a somewhat porous tissue composed of thin plates, known as lamellae, and usually containing cavities filled with a network of connective tissue called myeloid tissue, or marrow.
The external portion of bones enclosing all the components mentioned above includes the most compact and hardest of all bone tissue, which is in turn generally sheathed by a vascular, fibrous membrane known as the periosteum.