The colour of the hair is given by the presence of minute grains of colouring matter, like those in the cuticle of the Negro. They are formed in the cells at the root of the hair, and pass up with them into its structure. The quantity of colouring matter is usually slight in infancy and childhood, and increases during adolescence. Hence the hair becomes darker as we grow up. It is more or less deficient in the grey hair of old age; and in the instance of Marie Antoinette, and others whose hair is said to have turned grey in a few hours, the colouring matter is supposed to have been destroyed by some fluid, formed from the blood, and passing, through the pulp, into the hair. The hairs serve to protect the skin; and, as a general rule, they are most abundant upon the parts which are most exposed, and which, therefore, stand most in need of such protection. They are scattered over the back of the hand. On the palmar surface they are not required, and they would have interfered with the sense of touch; and we do not, accordingly, find them there, nor upon the sole of the foot, nor upon the edges of the lips. In certain parts of some animals, however, they serve as valuable adjuncts to the tactile organs by extending the range within which the contact of surrounding substances is felt. Thus the whiskers of the cat are set upon papillæ so sensitive that the slightest touch upon any part of the hair is felt; and the animal is thereby assisted in threading its way in the dark. This provision, added to the mode in which their feet are muffled with soft hair and their claws are retracted, enables the members of the feline tribe to steal with almost absolute stillness upon their prey. _Oil-glands._ [Illustration: Fig. 83. Hair, and Oil-glands.]