According to Pincus, the life of a hair ranges from two to six years, after which it falls out, to be replaced by a new one. In this way about fifty or sixty hairs are normally shed every day. In order to have thick, luxuriant, silky hair great attention must be paid to the condition of the scalp, since it is the scalp which contains the blood-vessels that nourish the hair. The scalp should be thick and pliable and move freely over the bones of the skull. If the scalp is drawn tightly over the bones of the skull, it tends to constrict the blood-vessels, and so lessen the supply of blood to the scalp and cause atrophy of the roots of the hair from pressure. The hair has a great tendency to accumulate dirt. It catches the dust flying in the air, and also retains the secretion of fat and the desquamated epithelium of the scalp and the products of perspiration. The two chief causes of the premature thinness of the hair are a deficient circulation of blood in the scalp and dandruff, and it is said that dandruff causes the loss of hair in 70 per cent. of all cases. =Dandruff.=—The last few years has witnessed a revolution in the views of the skin specialists in regard to the cause of dandruff. Previous to that time it was considered as simply a collection of epithelial scales mixed with more or less oily matter. Now, following the investigations that were first instituted by Unna, dandruff is considered as a symptom of a parasitic disease of the scalp, called seborrheic eczema. Sabouraud believes that the same parasite that produces seborrhea causes the loss of hair. It is believed that the parasite grows down into the hair follicle, between its walls and the hair. Seborrheic eczema is a chronic desquamative inflammation of the scalp of bacterial origin. It is divided into two stages: the first may last from one to seven years; it is attended with more or less dandruff in the form of scales and dryness of the hair; or the dandruff may unite with the oil, producing fatty crusts which are removed with difficulty. This is followed by the second stage, in which the hair falls out. _Symptoms of Seborrheic Eczema._—In the dry form of the disease, in which there is a scaling of the scalp, the hair is dry and unmanageable, the head itches, especially when the patient sits under a light or becomes overheated. There is a more or less constant falling of the scales upon the clothes. The scalp looks pale, and will be found covered with fine grayish or yellowish, readily detachable scales. Sometimes there is more or less redness of the scalp. This is the mildest grade of the disease. That dandruff is contagious has been proved by experiment, experience, and treatment. Lassar and Bishop made a pomade of the scales taken from the head of a student who was suffering from this disease, and rubbed it into the backs of guinea-pigs, which caused the same disease in them, and falling out of the hair.