86 THE MICROSCOPE. 



cealed within the skin; they are oblong in shape, 

 and seem to be composed principally of round cal- 

 careous bodies, arranged in many regular concentric 

 series. The scale of the eel is a beautiful object for 

 the polariscope. 



If you will pluck a hair out of your head, and hold 

 it between your forefinger and thumb, with the root of 

 the hair upwards, and then move your finger and 

 thumb up and down, you will notice the hair to 

 ascend ; now do the same with the root downwards, 

 and the hair descends. How is this ? Let us examine 

 its structure under the microscope. Under a magni- 

 fying power of about 400 diameters, you will notice 

 that the outer surface of the hair is marked by irregular 

 lines, the indications, as Dr. Carpenter remarks, of 

 the imbricated arrangement of the flattened cells or 

 scales which form the cuticle layer, for all hairs 

 essentially consist of two elementary parts, a ciiticle, or 

 investing substance, of a dense horny structure, and a 

 medullary, or pith-like substance, usually of a much 

 softer texture, occupying the interior. The cuticle 

 part consists of flattened scales arranged in an imbri- 

 cated manner ; the medullary substance is composed 

 of large spheroidal cells. In human hair the cuticle 

 layer is very thin ; the medullary portion, which is of 

 a fibrous nature, constitutes the principal part of the 

 shaft of the hair. These fibres may be separated from 

 each other if the specimen be macerated in sulphuric 

 acid for a time, and then crushed between two pieces 

 of glass. Each fibre is a long spindle-shaped cell. 

 The imbricated scales of the cuticle layer may be 

 isolated if the specimen be treated with an acid or an 

 alkali. It is in consequence of the position of these 

 imbricated scales that the upward or downward motion 

 of the hair, when moved between the finger and 

 thumb, takes place, the ed^es of the scales being 



