HAIR. 117 



which consists of several layers of cells. It is the 

 epidermis which is raised and covers the bladders 

 formed by the action of a blister applied to the skin. 



Hair. The hair consists of long solid filaments 

 (PL IX. fig. 9), and not of hollow tubes, as was 

 formerly supposed. It presents varieties of structure 

 in different animals, which agree generally in animals 

 belonging to the same Orders. 



Hairs are implanted in pits in the skin; each is 

 swollen at the base to form the bulb, which is seated 

 upon a papilla of the skin, by which it is formed or 

 secreted. The hair is an epidermic formation, con- 

 sisting of epidermic cells more or less flattened and 

 altered in shape by mutual pressure. 



The colour of the hair is usually seated in the outer 

 or cortical portion of the stem or shaft, and arises 

 from the presence of aggregations of minute granules 

 of colouring-matter or pigment, as the colouring-mat- 

 ter of animals is called : in the human hair it forms 

 short longitudinal stripes (fig. 9). In the central 

 pith or medullary portion of the hair the cellular 

 structure is more open and distinct than in the cortical 

 portion, in which the cells are so compressed and 

 consolidated as only to exhibit the cell-structure after 

 treatment with reagents; and the medullary cells 

 often contain air. 



In grey or white hairs, the whiteness depends 

 mainly upon the presence of air in the cells of the 

 pith. In the gnawing or rodent animals, as the 

 mouse or the rabbit, the pigment is partially at least 

 situated in the cells of the medulla. 



In the hairs of many animals, the cuticular or sur- 

 face-cells of the shaft are distinctly imbricated (fig. 5), 

 and form beautiful microscopic objects. 



The principal interest in the structure of the hair 

 relates to the three points above mentioned, viz. the 

 position of the pigment, the arrangement of the cuti- 

 cular cells or scales, and that of the cells of the pith. 



