FORMATION OF THE TISSUES HAIR. 



475 



of it ; as is shown by the results of recent inquiries into its structure. Most 

 Human hairs consist of two distinct substances ; an external, cortical, hard and 

 fibrous part ; and an internal, medullary, granular portion. Although, when 

 Hairs are moderately magnified, they look like empty tubes,- it is clearly 

 proved, by making fine transverse sections of them, that no central aperture 

 exists ; the hollow cylinder of cortical substance being completely filled up 



[Fig. 1C8. 



[Fig. 109. 



A Hair from an adult as seen under the nrero- A magnified view of a small Hair from the 



scope ; 1. 1, the follicle of the hair ; 2. its orifice ; face of a man. removed with its follicle and seen 



:, the base of the follicle ; 4, pulp of the hair: 5, under the microscope ; 1, 1, its follicle ; 2, root of 



its root; 6, the bulb in which the pulp is inserted; the hair; 3, its trunk; 4, its extremity ; 5, its cor- 



7. trunk of the hair; 8 the portion which projects tical or external substance; 6, its internal or 



beyond the skin.] medullary substance.] 



the surface of the pulp. This, however, proves to be a very erroneous account 

 with the granular medulla. The cortical substance of the hair is fibrous ; the 

 outlines of the component fibres being indicated by very delicate longitudinal 

 striaB, which may be traced in it, through its whole thickness. The diameter 

 of these fibres is stated by Henle at about l-4000th of an inch ; but, by mace- 

 ration in hydrochloric acid, they may be split, according to Bidder, into fibrilla? 

 of no more than l-27,000th of an inch in diameter. Besides exhibiting these 

 longitudinal striae, the surface of the hair presents a series of transverse and 

 oblique, and sometimes apparently spiral wavy lines, arrange^ in a very close 

 series ; these have been shown to be due to the slightly-projecting edges of 

 tiers of minute scales, like those of the epidermis, but much smaller ; which 

 invest the whole surface of the hair, forming a sheath around its cortical part. 

 The Medullary portion of the Hair seems composed of minute globules, like 

 pigment-granules, or drops of oil agglomerated in small lumps, and enclosed 

 in a membrane which lines the tube of cortical substance ; along this mem- 



