58.  The Bones in After Life.  Popular impression attributes a less share of life, or a lower grade of vitality, to the bones than to any other part of the body.  But really they have their own circulation and nutrition, and even nervous relations.  Thus, bones are the seat of active vital processes, not only during childhood, but also in adult life, and in fact throughout life, except perhaps in extreme old age.  The final knitting together of the ends of some of the bones with their shafts does not occur until somewhat late in life.  For example, the upper end of the tibia and its shaft do not unite until the twenty-first year.  The separate bones of the sacrum do not fully knit into one solid bone until the twenty-fifth year.  Hence, the risk of subjecting the bones of young persons to undue violence from injudicious physical exercise as in rowing, baseball, football, and bicycle-riding.

The bones during life are constantly going through the process of absorption and reconstruction.  They are easily modified in their growth.  Thus the continued pressure of some morbid deposit, as a tumor or cancer, or an enlargement of an artery, may cause the absorption or distortion of bones as readily as of one of the softer tissues.  The distortion resulting from tight lacing is a familiar illustration of the facility with which the bones may be modified by prolonged pressure.

Some savage races, not content with the natural shape of the head, take special methods to mould it by continued artificial pressure, so that it may conform in its distortion to the fashion of their tribe or race.  This custom is one of the most ancient and widespread with which we are acquainted.  In some cases the skull is flattened, as seen in certain Indian tribes on our Pacific coast, while with other tribes on the same coast it is compressed into a sort of conical appearance.  In such cases the brain is compelled, of course, to accommodate itself to the change in the shape of the head; and this is done, it is said, without any serious result.

59.  Sprains and Dislocations.  A twist or strain of the ligaments and soft parts about a joint is known as a sprain, and may result from a great variety of accidents.  When a person falls, the foot is frequently caught under him, and the twist comes upon the ligaments and tissues of the ankle.  The ligaments cannot stretch, and so have to endure the wrench upon the joint.  The result is a sprained ankle.  Next to the ankle, a sprain of the wrist is most common.  A person tries, by throwing out his hand, to save himself from a fall, and the weight of the body brings the strain upon the firmly fixed wrist.  As a result of a sprain, the ligaments may be wrenched or torn, and even a piece of an adjacent bone may be torn off; the soft parts about the injured joint are bruised, and the neighboring muscles put to a severe stretch.  A sprain may be a slight affair, needing only a brief rest, or it may be severe and painful enough to call for the most skillful treatment by a surgeon.  Lack of proper care in severe sprains often results in permanent lameness.