HAIR. 265 



division : thus the root consists of the prolongation of the 

 hair proper, or stem, terminating in an expanded portion 

 which has been termed the bulb, and of a double sheath; 

 the stem also is divisible into cortex, medulla, and inter- 

 vening fibrous portion, which constitutes the chief bulk of 

 the hair. (See Plates XXVIII. and XXIX.) 



These divisions of the root and stem of hairs suggest its 

 comparison to a tree, the stem of which also resolves itself 

 into cortex, medulla and intervening woody or fibrous sub- 

 stance. The comparison is also heightened by the similar 

 relation in which both stand to the parts around them, viz. 

 the soil in the case of the tree, and the dermis in that of the 

 hair. 



Root of Hair. 



We will first describe the root, because it is the source 

 from which the hair is developed : this, as already noticed, 

 consists of two parts, the sheath and the bulb. 



The Bulb. The bulb is the expanded and basal portion 

 of the stem of each hair : it is usually two or three times 

 the diameter of the hair itself, and is sometimes excavated 

 below : it is constituted of granular cells, which are either 

 circular, angular, or elongated in form, the spherical cells, 

 form the extremity of the bulb, the polygonal ones its sur- 

 face, and the elongated cells are placed above the spherical 

 ones, of which they are modifications, and beneath the an- 

 gular cells of the surface of the bulb. Acetic acid will be 

 found useful in displaying the cellular structure of the bulb. 



In healthy hairs this bulbous portion of the stem is al- 

 ways coloured, which is not the case with grey hairs. (See 

 Plate XXVIII.) 



The part of the stem of the hair immediately above the 

 bulb, and included within its sheath, exhibits the structure 

 of the body of the stem itself, being divisible into scaly 

 cortex, fibrous intervening substance, and granular medulla. 



Sheath. The bulb and lower portion of the stem of the 



z 2 



