PHYSIOLOGICAL ANATOMY OF THE HAIRS. 



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membrane, composed of flattened cells, generally without nuclei. This 

 extends from the bottom of the hair-follicle and covers the lower two-thirds 

 of the root. 



Structure of the Hairs. The different varieties of hairs present certain 

 peculiarities in their anatomy, but all of them are composed of a fibrous 

 structure forming the greater part of their substance, covered by a thin layer 



FIG. 109. Human hair from the head of a white 

 child ; magnified 370 diameters (from a pho- 

 tograph taken at the United States Army Med- 

 ical Museum). 



This figure shows the imbricated arrangement of 

 the epidermis of the hair. 



FIG. 110. Transverse section of a human hair 

 from the beard of a ivhite adult ; magnified 

 370 diameters (from a photograph taken at the 

 United States Army Medical Museum). 



of imbricated cells. In the short, stiff hairs, and in the long, white hairs, 

 there is a distinct medullary substance ; but this is wanting in the downy 

 hairs and is indistinct in many of the long, dark hairs. 



The fibrous substance of the hairs is composed of hard, elongated, longi- 

 tudinal fibres, which can not be isolated without the aid of reagents. They 

 may be separated, however, by maceration in warm sulphuric acid, when 

 they present themselves in the form of dark, irregular, spindle-shaped plates. 

 These contain pigmentary matter of various shades of color, occasional cavi- 

 ties filled with air, and a few nuclei. The pigment may be of any shade, 

 between a light yellow and an intense black ; and it is this substance that 

 gives to the hair the great variety in color which is observed in different 

 persons. In the lower part of the root the fibres are much shorter, and at 

 the bulb they become transformed, as it were, into the soft, rounded cells 

 found in this situation, covering the papilla. 



The epidermis of the hair is very thin and is composed of flattened, 

 quadrangular plates, overlying each other from below upward. These scales, 

 or plates, are without nuclei, and they exist in a single layer over the shaft 

 of the hair and the upper part of its root ; but in the lower part of the root, 

 tne cells are thicker, softer, are frequently nucleated, and they exist in two 

 layers. 



The medulla is found in the short, stiff hairs, and it is often very distinct 



