HAIR. 277 



GREY HAIR. 



If a grey hair be contrasted with an unaltered one from 

 the head of the same person, the following differences will be 

 noticed between the two. The grey or white hair will be 

 observed to be almost colourless, the bulb and fibrous portion 

 will be destitute of colour, the medulla alone retaining a 

 slight degree of coloration : this, however, is collapsed, and 

 in place of being continuous throughout its length, will be 

 seen to be interrupted at intervals. (See Plate XXVIII. 



fig- 2.) 



The unaltered hair, on the contrary, is distinguished by 

 characters the reverse of those exhibited by the grey hair ; 

 thus the bulb, stem and medulla are all deeply coloured, and 

 the latter fills the entire cavity of the medullary canal, and is 

 continuous throughout. (See Plate XXVIII. Jig. 1.) 



Grey hair retains a considerable degree of vitality, as is 

 proved by its growth continuing for many years after its loss 

 of colour. 



PROPERTIES OF HAIR. 



Hairs are remarkable for their strength, their elasticity, 

 durability, and for the difficulty with which they undergo 

 the process of decomposition : their strength results probably 

 from their fibrous constitution ; in their elasticity and dura- 

 bility, they partake of the character of all horny structures. 



The strength of hair is proved by the fact that a single 

 hair will bear a weight of 1150 grains. 



Its elasticity is shown by the readiness with w r hich each 

 hair, when extended, returns to its original size and shape, 

 as well as by the fact that the numerous hairs forming a 

 curl or lock will recover their ordinary form and disposition 

 after extension. 



Its durability is shown by the persistence of hairs through- 

 out many years of life. 



Lastly, its indestructibility is proved by the occurrence of 

 hairs in the tombs of persons buried for ages. 



