The lack of sufficient nutritive salts in the diet is often revealed by the condition of the teeth. From a physiological standpoint the teeth are no less important than the brain, the eyes and the hair; and the conclusion that perfect eyes, hair and teeth indicate a perfect brain is absolutely justified, while the lack of perfection in these organs shows internal deficiencies long before they appear in external manifestation in the form of disease. Since healthy blood is the basic condition of healthy teeth, the fact that people have clean white teeth, set in regular line, indicates the existence of healthy blood. On the other hand, a bad composition of the blood is manifested by short, irregularly set, yellowish teeth. The teeth of healthy people are always somewhat moist, dry teeth are accordingly a bad sign. The only advantage of yellowish teeth rests in the fact that their dentine is, as a rule, stronger. Extremely bluish white teeth often consist of a soft, porous and tender dentine. Faulty structure of the teeth indicates weak bones in general. Crippled teeth and the late appearance of teeth in infants,--that is, not before the ninth month,--are symptoms of rachitis. Healthy children have their teeth between the fifth and seventh months. The teeth of diabetics become loose without any formation of tartar, (an incrustation of phosphate of lime and saliva). Extremely yellow teeth indicate jaundice, while reddish teeth show hyperaemia of the dentine. Carious teeth are a result of disturbed circulation. The gums are also very indicative of disease. If they are of a pale pink colour, they indicate anaemia or chlorosis; if bluish red on the edge, they indicate tuberculosis. Some of the most striking indications of existing disease are demonstrated by the _neck_. By feeling the neck and carefully watching its external appearance, the experienced scientist will obtain much valuable information that will aid in his diagnosis, and give him additional knowledge as to the processes going on within the body of the patient. The significance of the formation of the _thorax_ (_chest_) is well known, even to many laymen. Flat chest, so-called chicken chest, indicates imperfect development of the lungs, and when extreme, even tuberculosis. A flabby abdomen indicates disposition to hernia and stagnation of the blood, frequently causing hemorrhoids or inflammation of the prostate gland in men, and all kinds of diseases--inflammatory or catarrhal--in women. As to the _legs_, the so-called varicose veins are indications of weak blood-vessels and intestinal hemorrhage, while inflamed nerves lead to the conclusion of gouty diathesis and the danger of paralytic strokes. The _skin_ usually affords more indications that aid in forming a correct diagnosis than is usually recognized.