132 



HEALTH AND DISEASE 



of each cell is perfectly well defined on the surface of the hair, as can 

 be seen by examination under a moderate magnifying power. The epi- 

 dermis extends into the follicle very near to the bulb. Within the 

 epidermis or outer layer is the cortical substance of the hair, in which 

 the pigment granules, to which it owes its colour, are distributed. The 

 cortical substance forms the chief part of the bulk of the hair. It is 

 composed of long elliptical fibres, which may be reduced to their elements, 

 i.e. epithelial lamellae with their nuclei. Under the microscope this 

 portion of the hair exhibits the appearance of longitudinal stripes or fibres. 

 The third portion of the hair is the so-called medullary substance; this 

 occupies the narrow cavity in the centre, which extends from the bulb 

 upward towards the point. The hair follicle, in which the root is em- 

 bedded, is really an involution or doubling down of the skin itself. It 



presents for notice, proceeding from 

 the inside of the follicle, a membranous 

 structure, consisting of cells similar to 

 those forming the deep layer of the 

 cuticle, rete mucosum, on which is 

 imposed the internal sheath of the 

 hair, in reality the involuted epidermis. 

 Besides hair of the ordinary kind 

 as described, there are certain varieties 

 which present special characters. For 

 example, what is ordinarily described 

 as " horse hair", and employed for 

 the purpose of stuffing cushions and 

 weaving into coverings, is an extremely 

 coarse variety, occurring in the fore- 

 lock between the ears, passing along to the top of the neck as far as 

 the withers, constituting the mane, existing also upon the margin of the 

 eyelids, eyelashes, and growing here and there on the outside of the 

 lips and below the eyes, described as tentaculae. These coarse hairs are 

 developed in the most prominent form upon the tail, from which they 

 grow to an extraordinary length, reaching almost to the ground if left 

 uncut. Similar hairs also grow at the back of the fetlock joints, in- 

 vesting the horny growth which is known as the ergot. 



The variety of hair which is described as wool, is distinguished by 

 its fineness and softness. It does not, however, under the microscope, 

 present any elements which differ from those already described. 



Horn. This structure may be correctly described as a form of hair 

 cemented together into a dense mass, and employed to protect those parts 



Fig. 261. Section of Hair Follicle 



A, Dermio Coat of Follicle. B, Outer Layer of 

 Dermic Coat with Blood-vessels, c, Inner Layer 

 of Dermic Coat. D, Epidermic Coat or Root-Sheath. 

 E, Inner Root-Sheath. F, Hair, o, Lymph Space. 



