_Hair._--Greying or whitening of the hair occurs commonly in old age, but not universally for some centenarians have retained the natural colour of the hair; coarse jet-black hair is specially prone to whiten early. The change in colour has been ascribed by Metchnikoff to the action of phagocytes (chromophages) which invade the roots of the hairs and carry off the pigment granules. Like the arcus senilis it may occur quite early in life and without any other indication of age, and is often hereditary; as the sage of Norwich wrote, “Hairs make fallible Predictions, and many Temples early Gray have outlived the Psalmist’s Period.”[141] Lord Bacon[142] indeed said, “Hasty gray hairs, without baldness, is a token of long time; contrarily, if they be accompanied by baldness.” But baldness is often due to seborrhoea and so only secondarily connected with advanced age. In some rare instances the hair already grey or white has been known to regain its normal colour; the late Sir Charles Cameron[143] recorded this event in his own life after an accident confining him to bed for some months in his eightieth year, and refers to the hair of a man aged 90 years returning to its original brown colour; cases were also reported by Graves.[144] Velasquez de Tarente[145] recorded an abbess who after an illness which promised to be fatal in her hundredth year had a crop of brown hair, and, like Sir Charles Cameron, put on weight. Four other cases are given by Sir John Sinclair[146] in persons aged 80, 104, 105, and 114 years. Baldness may be definitely due to thyroid insufficiency and not to atrophy of the hair follicles and sebaceous glands. A pensioner aged 75, whom I saw with Major R. J. C. Thompson, in the Royal Hospital, Chelsea, with baldness and a grey beard, was given thyroid extract, as he was thought to have hypothyroidism; his general condition then improved wonderfully, and his scalp became covered with dark brown hair which had to be cut at intervals. Parkinsonian tremor was rather more obvious during the first six months that he was on thyroid treatment. The hair of the body may become scanty and lose its tendency to curl. Excessive growth of hair (hypertrichosis) in women after the menopause is an indication of disordered endocrine balance (loss of ovarian internal secretion?) and is only so far an accompaniment of age; it may be seen in comparatively young women from various causes. _The nails_ are often longitudinally ridged, brittle, hard, and thickened; but onychogryphosis is rather the result of neglect or of disease than solely of old age.