In olden time, the hair was said to be produced by “a vapour or excrement of the brain.” In the more exact language of science it is described as a horny appendage of the skin. The skin is shown to be composed of two layers--the outer termed the cuticle, the inner the cutis. The cuticle is an insensible transparent membrane covering the whole surface of the body; the portion exposed to the air consists of flattened cells or scales which are continually being renewed; while on the inner surface, in contact with the cutis, is a soft mucous substance, in which are situate the pigment cells giving the characteristic colour peculiar to race and climate. The cutis is composed of the layer of minute papillæ, the principal seat of the sense of touch, covering an intricate arrangement of fibrous tissue, which receives the delicate ramifications of the nerves and arteries. The sheath from which the hair protrudes above the skin is formed by a tubular depression of the cuticle which reaches below the cutis to the subjacent fat and cellular tissue; the lower end of the sheath is shaped like a pouch, and contains the pulp from which the bulb and shaft of the hair are formed in successive portions--the most recent pushing forward that previously formed. The bulbs are larger in young than in old hairs, and are implanted obliquely in respect to the cuticle. The shaft of the hair being formed by an aggregation of parts, has been likened to a pile of thimbles one resting within the other; this overlapping of the outer coating of scales gives rise to that roughness which we feel on passing the fingers along a hair from the point to the bulb, though apparently perfectly smooth when held in the opposite direction. The colouring matter of the hair is seen in the pulp, and is distributed between the cells composing the shaft. In form the hair may be described as a flattened cylinder, not, however, hollow or filled with a kind of pith as is usually supposed; but solid throughout and formed of a homogeneous mass of a cellular texture. From the extreme minuteness of its structure, and the mystery which shrouds all vital processes, it is still a question as to whether the shaft of the hair is permeable by fluids derived from the blood. The old notion of a circulation within the hair like the sap in vegetables is disregarded; but it is contended that absorption does take place, and that fluids are transmitted to the extreme point of the hair. In proof of this we are referred to the sudden change of colour which the hair undergoes in extraordinary cases of mental emotion, as instanced in the sufferings of Marie Antoinette, whose hair was found to have turned grey with grief. It is assumed that the altered condition of the blood acting chemically upon the fluids of the hair destroys the colour. If this be granted, we must look for minor changes in the colour of the hair with every ordinary change in the normal condition of the blood.