252 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



edges forming delicate lines upon the surface of the hair, which are sometimes 

 transverse, sometimes oblique, and sometimes apparently spiral (Fig. 42, A). 

 Within this we find a cylinder of fibrous texture, which forms the principal part 

 of the shaft of the hair ; the constituent fibres of this substance, which are marked 

 out by delicate longitudinal striae that may be traced in vertical sections of the 

 hair (Figs. 42, B, 43, 6), may be separated by crushing the hair, especially after 

 maceration in acid ; and each of them consists, as has been shown by Prof. Kol- 

 liker, 1 of a fasciculus of flattened cells of a fusiform outline. It has been further 

 shown by Kblliker, that the color of this portion of the hair is due, not only to 

 the presence of pigmentary granules, either collected into patches, or diffused 

 through its substance ; but also to the existence of a multitude of lacunulse con- 

 taining air, which cause it to appear dark by transmitted and white by reflected 

 light. Within the hollow cylinder of fibrous substance, is found a canal which 

 is occupied by the medullary portion of the hair (Fig. 42, c); this consists of 



Fig. 42. 





Structure of Human Hair: A, external surface of the shaft, showing the transverse striae and jagged boun- 

 dary, caused by the imbrications of the scaly envelop ; B, longitudinal section of the shaft, showing the fibrous 

 character of the cortical substance, and the arrangement of the pigmentary matter ; c, transverse section, 

 showing the distinction between the transparent envelop, the cylinder of cortical substance, and the medul- 

 lary centre ; D, another transverse section showing deficiency of medullary substance. Magnified 310 diameters. 



cells which retain more or less of the spheroidal shape (Fig. 43, a); and it gene- 

 rally presents a darker hue than the cortical substance, partly through the pre- 

 sence of a larger quantity of pigmentary matter in its cells, but chiefly through 

 the greater number of air-spaces that lie amongst them. The medullary sub- 

 stance, however, is not unfrequently wanting j being usually deficient in the fine 

 hairs scattered over the general surface of the body, and not being always present 

 in the ordinary hairs of the head (D). The chemical composition of Hair, as 

 already stated, is precisely the same with that of the horny Epidermis ( 240). 

 Its coloring matter seems related to Haematine ; it is bleached by Chlorine j 

 and its hue appears to be dependent in part upon the presence of iron, which is 

 found in larger proportion in dark than in light hair ( 87). 



246. The real nature of the different components of the Hair, and their rela- 

 tion to those of the Epidermis, is ascertained by examining them at its base, 

 and tracing their origin and connections. The hair expands at the base of the 

 shaft into a bulbous enlargement; and this is lodged within a follicle, formed 

 by a depression of the Cutis, and lined by a continuation of the Epidermis. 

 The exterior of this follicle (Fig. 43) is bounded by a fibrous membrane, derived 

 from the Corium, whose fibres are longitudinally arranged (&); within this is 

 another layer whose fibres lie transversely (i); and within this, again, is a struc- 



Mikroskopische Anatomic," band ii. p. 105. 



