HAIR OP MOLE. 215 



CHAPTER XII. 

 ; HAIRS. 



HUMAN HAIR. 



THE interest of these slides is greatly increased by view- 

 ing them with polarized light, as they give beautiful colours 

 over the selenite stage. But, besides the mere play of 

 colour, it is worthy of observation that the hairs of animals 

 and insects are so variously fashioned and so delicately 

 finished, that each species has in some cases a distinct form, 

 though to unassisted eyes they are perfectly alike. The 

 structure of hair is cellular, like every other part of the 

 body, and if it is soaked in acetic acid, or soda, that appa- 

 rent tube is found to be made up of scales outwardly, 

 pigment cells, linear cells, and[ nucleated cells within; 

 growing] from the skin in which it is planted, having a 

 bulb-like root, nourished by ducts and follicles, or small 

 pouches on either sides of the hair-bulb. 



When a human hair is young and healthy, it has abun- 

 dant pigment cells, and therefore is coloured; but, when 

 old or diseased, either the pigment cells become empty, or 

 only filled with air, or it is preyed upon by fungi, several 

 species of which infect the human hair. 



HAIRS OF DORMOUSE AND COMMON MOUSE 



show a beautiful arrangement of air-cells, and if soaked in 

 potash these become more visible, with the medullary cells 

 in two rows. 



HAIR OF MOLE. 



The cells in the medulla very distinct. 



