STRUCTURE OF HAIRS. ccix 



although this term is more properly applied to the superficial coating of 

 scales above mentioned. The fibrous substance is translucent, with short 

 longitudinal opaque streaks of darker colour intermixed. It may be 

 broken up into straight, rigid, longitudinal fibres, which, when separated, 

 are found to be flattened, broad in the middle, where they measure 4^-5- 

 of an inch in breadth, and pointed at each end, with dark and rough edges. 

 The fibres may be resolved into flattened cells of a fusiform outline ; these 

 are mostly transparent, or marked with only a few dark specks. The 

 colour of the fibrous substance is caused by oblong patches of pigment- 

 granules, and generally diffused colouring matter of less intensity. Very 

 slender elongated nuclei are also discovered by means of reagents, whilst 

 specks or marks of another description in the fibrous substance are 

 occasioned by minute irregularly shaped cavities containing air. These 

 air-lacunules are abundant in white hairs, and in very dark hairs may be 

 altogether wanting ; they are best seen too in the former, in which there is 

 no risk of deception from pigment-specks. Viewed by transmitted light 

 they are dark, but brilliantly white by reflected light. When a white hair 

 has been boiled in water, ether, or oil of turpentine, these cavities become 

 filled with fluid, and are then quite pellucid ; but when a hair which has 

 been thus treated is dried, the air quickly finds its way again into the 

 lacunae, and they resume their original aspect. 



The medulla or pith, as already remarked, does not exist in all hairs. 

 It is wanting in the fine hairs over the general surface of the body, and is 

 not commonly met with in those of the head ; nor in the hairs of children 

 under five years. When present it occupies the centre of the shaft and 

 ceases towards the point. It is more opaque and deep-coloured than the 

 fibrous part ; in the white hairs of quadrupeds it is white, but opaque and 

 dark when seen by transmitted light. It seems to be composed of little 

 clusters of cells, differing in shape, but generally angular, and containing 

 minute particles, some resembling pigment-granules, and others like very 

 fine fat-granules, but really for the most part air-particles, apparently 

 included in some solidified tenaceous substance. The whole forms a con- 

 tinuous dark mass along the middle of the stem, interrupted at parts for a 

 greater or less extent. In the latter case, the axis of the stem at the inter- 

 ruptions may be fibrous like the surrounding parts, or these intervals may 

 be occupied by a clear colourless matter ; and, according to Henle, some 

 hairs present the appearance of a sort of canal running along the axis and 

 filled in certain parts with opaque granular matter, and in others with a 

 homogeneous transparent substance. 



The root of the hair is lighter in colour and softer than the stem ; it 

 swells out at its lower end into a bulbous enlargement or knob (fig. 

 cxiv. c), and is received into a recess of the skin named the hair-follicle, 

 which, when the hair is of considerable size, reaches down into the subcu- 

 taneous fat. The follicle, which receives near its mouth the opening ducts 

 of one or more sebaceous glands (k, fc), is somewhat dilated at the bottom, 

 to correspond with the bulging of the root ; it consists of an outer coat 

 continuous with the corium (fig. cxiv. g, h ; cxv. d, d), and an epidermic 

 lining (fig. cxiv. e, f ; cxv. 6, c), continuous with the cuticle. The outer 

 or dermic coat is thin but firm, and consists of three layers. The most 

 external is formed of connective tissue in longitudinal bundles, without 

 any elastic fibres, but with numerous long fusiform corpuscles. It is 

 highly vascular, and possesses nervous fibrils. It is intimately connected 

 above with the corium, and determines the form of the follicle. The most 



