EPIDERMAL APPENDAGES. 



These may take place with great rapidity ; for at least one 

 case has occurred in hospital, under medical supervision, in 



in a single 



night from 



which the hair has grown white 

 anxiety, and there is, therefore, no 

 reason to doubt the historical traditions 

 of similar occurrences. The appearance 

 in one night also of single white hairs 

 without any special disturbance of the 

 system, has been noted by competent 

 observers, and is probably a very com- 

 mon occurrence. 



The sensation of the hair standing 

 erect from emotional or other causes is 

 accounted for by the fact that a band 

 of unstriped muscle descends from tho 

 corium, and is attached to the lower 

 part of the hair follicle on the side 

 towards which the hair is sloped, so 

 that by its contraction it pulls the root 

 of the hair into the vertical position. 



The first commencement of a hair in 

 the embryo consists of a thickening of 

 the cuticle by growth downwards into 

 the coriuin ; and within the mass of 

 cells so deposited the form of the hair 

 makes its appearance with a slender 

 shaft and a large bulb, into which a 

 papilla from the corium projects. Then, 

 in the process of growth, the young hair bursts through the 

 cuticular sheath in which it has been enveloped, and projects 

 on the surface. 



Fig. 42. DEVELOP- 

 MENT OF A HAIE,. A, 

 Downward growth of 

 epidermis. B, Form 

 of the hair completed 

 before appearing on the 

 surface. After Kolli- 

 ker. 



