=Why Candy and other Sweets cause the Teeth to Decay.=--A sour substance called acid usually starts the decay of a tooth by eating through the enamel. Germs change sugar and other sweets into an acid. The acid is not made at once. An hour or more is needed for the germs to grow to form the acid. If, after eating sweet foods, the mouth is well cleaned, no acid will be formed. Sugar and candy do not, therefore, spoil the teeth unless it is left sticking about them. =How to brush the Teeth.=--Every boy and girl should own a toothbrush. _The teeth should be brushed every night and morning and kept white._ Yellow or gray slimy teeth are very ugly. The teeth should be brushed on the inside as well as on the outside. It is best to brush the teeth crosswise for two minutes and then spend another two minutes brushing the upper teeth downwards and the lower teeth upwards. This prevents pushing the gum away from the teeth. Plenty of water should be used with the brush, and a little good powder is helpful once a day. =How the Dentist can Help.=--Sometimes the milk teeth do not get loose so that they can be pulled with the fingers at the right time. The second teeth then come in at one side and may never get straight in place. They then spoil the appearance of the face and do poor work in chewing. The dentist should be asked to help straighten the teeth as soon as they appear crooked. [Illustration: FIG. 34.--Exact drawing of the teeth of two persons. Those in the lower picture began to decay over twenty-five years ago and they were then filled so as to remain perfect. The teeth in the upper picture began to decay less than ten years ago but were not filled.] It is wise to have the dentist examine the teeth once or twice every year and remove a limy substance called tartar collecting at their base. The dentist can stop the decay in a tooth by cleaning out the little hole and filling it with gold or some other material. It may cause a little pain and expense to have the teeth filled, but it will save a hundred times as much pain and expense later. The six year molars need special care as they are likely to decay early. Even the milk teeth often need filling so that they will not be lost too soon. =Bad Teeth cause Sickness.=--When anything decays, it is full of germs, and they are always giving off some poison. The poison may hurt the body and is likely to make parts of the mouth sore and tender so that other germs of disease can break through into the flesh. Disease germs can easily lodge in the holes of decaying teeth, grow in numbers, and finally cause diphtheria, sore throat, or other ailments. Four out of every five children suffering from diphtheria or other throat or ear troubles are found to have from one to ten bad teeth. You must keep good teeth if you wish to be well and strong.