Development of Special Senses.
—A new-born baby is unable to distinguish objects, but the eyes are sensitive to light and need careful protection. Hearing, although undeveloped at birth, soon becomes acute; consequently the child should stay in a quiet room. When six or eight weeks old he notices objects, and at three months old he welcomes his mother when he is hungry. A month or two later he begins to distinguish between familiar and unfamiliar faces, and to show approval or disapproval.
Development of Speech.
—A baby six or seven months old begins consciously to utter sounds, and usually can say a few unconnected words by the time he is a year old. The average child, however, does not begin to form sentences of more than two or three words until he is about two years old.
Development of Teeth.
—The so-called milk teeth are twenty in number; they are followed by thirty-two permanent teeth. The two lower front teeth (central incisors) generally appear when a child is from five to nine months old, and in from one to three months later the four upper front teeth (upper incisors) appear. All the first or milk teeth should have come through by the time a child is two and a half years old, but wide variations occur both in the time and order of
appearance and should occasion no uneasiness if the child seems well. Unusual conditions of any sort should be referred to the physician; it is a great mistake to attribute all illness at this time to teething.
The first of the permanent teeth appear when a child is about six years old. Mothers sometimes mistake the first permanent molars for temporary teeth, a mistake that frequently leads to neglect and even extraction of highly important teeth. All but the last four molars, sometimes called wisdom teeth, should be through by the time a child is fifteen. The wisdom teeth may not appear before the 20th or even the 25th year.