Morton Toth, age 13, of Haggerstown, Md., for his question:

WHAT EXACTLY IS BODY TISSUE?

Tissue, in physiology, is a group of similar specialized cells which carry out a particular function in the body. Body tissues are divided into numerous kinds. The chief division includes epithelial, muscular, connective or supporting and nervous tissues.

Blood and lymph are also usually considered tissues.

Epithelial tissues are coverings. Examples are the skin which covers the outside of the body, and membranes that line the body cavities which open to the outside. Glands are also derived from epithelial tissue.

Muscular tissue is made up of cells which can contract, and then relax again.

Connective tissue includes groups of cells which bind different parts of the body together or support the body. The chief types of connective tissue are fibrous, elastic, loose fiber elastic and adipos or fat. Cartilage and bone may also be said to be connective tissue.  Nervous tissue is made up of cells that carry nervous impulses.