Raymond Drasnin, age 12, of Charleston, West Virginia, for his question:

What are the body's blood forming mechanisms?

If these mechanisms were understood fully, the majority of human diseases could be eradicated. The living, moving blood stream teems with a multitude of bodies and biological factors    working together in subtle relationships. Medical researchers and molecular biologists are probing deeper into these mysteries. In the past decade their knowledge has multiplied at an enormous rate. However, most of the miraculous mechanisms of the blood still are unsolved.
We know most about the assorted floating cells that circulate in the watery plasma. The erythrocytes are manufactured in capillaries located in the central marrow tissue of the bones. They are stacked like saucers and released into the blood stream as needed. The train function of these red blood cells is to transport oxygen and carbon dioxide between the lungs and living tissues.
Some of the various leucocytes are manufactured in cells located outside the bone marrow. These armies of white blood cells defend the body from invading antigens. The platelets are assembled in the bone marrow from fragments of cytoplasm. They function in the complex blood clotting operation. The tiny percentage of monocytes are assembled in the spleen and bone marrow and released to engulf hostile antigens. The lymphocytes are manufactured in the spleen, the lymph glands and lymphoid tissues. They are shared by the blood and the lymph system and provide the body with certain immunities. The pulsing blood and the lacy lymph system transport these assorted cells to the line of duty.
We need to know much more about these mobile blood cells. However, our understanding of the vital plasma has barely begun. This pale watery fluid makes up 55 per cent of the living blood. Its delicately balanced blend of biochemicals protects, nurtures and sustains the floating cells and performs numerous other functions, mostly unknown. For examples a certain plasma protein plays a vital role in the clotting activity. This known clotting factor totals only enough to cover about 25 small pinpricks. But other plasma factors involved in this intricate teamwork are not fully understood. Researchers suspect that hundreds of them still are undetected.
The multitude of biochemicals in the blood are manufactured from carbon and nitrogen, oxygen and hydrogen, plus smaller amounts  of many other simple ingredients. Many are digested food elements which the blood absorbs from the intestine. Traces of hormones are secreted into the blood by the endocrine glands. The water content is absorbed in adjusted doses, mainly from the kidneys.
The strongest microscopes reveal only shadowy images of molecular factors. What's more, most chemical activities stop when a blood sample is taken from the living body to be studied. Researchers hope for major breakthroughs in both instruments and techniques. They have amassed enough facts to stuff a room full of books. However, a vast library of empty pages is waiting for the complete story of the blood.