NUTRITION OF HAIB. 



377 



out without pain, is one that has lived its natural time, 

 and has died, and been separated from the living parts. 

 In its bulb such an one will be found different from those 

 that are still living in 

 any period of their age. 

 In the early period of 

 the growth of a dark 

 eyelash, the medullary 

 substance appears like 

 an interior cylinder of 

 darker granular sub- 

 stance, continued down 

 to the deepest part, 

 where the hair enlarges 

 to form the bulb. This 

 enlargement, which is 

 of nearly cup-like form, 

 appears to depend on 

 the accumulation of 

 nucleated cells, whose 

 nuclei, according to 

 their position, are 

 either, by narrowing 



and elongation, to form the fibrous substance of the outer 

 part of the growing and further protruding hair, or are to 

 be transformed into the granular matter of its medullary 

 portion. At the time of early and most active growth, all 

 the cells and nuclei contain abundant pigment-matter, and 



* Fig. 102. Intended to represent the changes undergone by a hair 

 towards the close of its period of existence. At A, its activity of growth 

 is diminishing, as shown by the small quantity of pigment contained in 

 the cells of the pulp, and by the interrupted line of dark medullary 

 substance. At B, provision is being made for the formation of a new 

 hair, by the growth of a new pulp connected with the pulp or capsule 

 of the old hair. c. A hair at the end of its period of life, deprived of 

 its sheath and of the mass of cells composing the pulp of a living hair. 



