. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE SKELETON 377 continually, both from the inside and the outside surface of bone. Early in life, when the skeleton grows rapidly, the living part of bone exceeds the mineral matter in it. Bones of young people are frequently quite soft and flexible. Very early in life, almost all bones are formed of a tissue called cartilage. Microscopic Structure of Bone. —Gristle, the common name for car- tilage, is seen under the microscope to be made up of living cells surrounded by a clear, tough mat
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE SKELETON 377 continually, both from the inside and the outside surface of bone. Early in life, when the skeleton grows rapidly, the living part of bone exceeds the mineral matter in it. Bones of young people are frequently quite soft and flexible. Very early in life, almost all bones are formed of a tissue called cartilage. Microscopic Structure of Bone. —Gristle, the common name for car- tilage, is seen under the microscope to be made up of living cells surrounded by a clear, tough material, the latter formed by the action of the cells embedded in it. Formation of bone takes place in much the same way. In a piece of bone examined under the microscope are found hun- dreds of little irregular spaces. From these spaces radiate many tiny canals. These spaces, during the life of the animal, were occupied by bone-forming cells, irregular processes from which passed out into the canals. Later, limy mat- ter was deposited around certain of the cells. Thus true bone was formed. Hygiene of the Skeleton; Differences in Structure of the Skele- ton OF A Child and an Adult. — During childhood, because of the small amount of mineral matter and consequent lack of rigidity in bone, we must exercise some care in the treatment of the skeleton. A round-shouldered condition, brought on by sitting in an incorrect position, may cause a promi- nent deformity of the skeleton. Children are frequently allowed to walk before the leg bones are capable of supporting the weight of the body, thus causing bow-leggedness. Seats at school which force a child to take an incor- rect attitude when at rest are frequently the means of permanently deforming the vertebral column. Later in life, when the activity of the bone-forming cells ceases, more mineral matter is present than animal matter. A broken bone is thus much more serious at this time than in a young Bone, as seen under the
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