302 NUTRITION. 



tinned 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 the 

 whole bulb looks nearly black. The sources of the material 

 out of which the cells form themselves are at least two ; the 

 inner surface of the sheath or capsule, which dips into the 

 skin, enveloping the hair, and the surface of a vascular pulp 

 which fits in a conical cavity in the bottom of the hair-bulb. 



Such is the state of parts so long as the growing hair is all dark. 

 But as the hair approaches the end of its existence, instead of 

 the almost sudden enlargement at its bulb, it only swells a 

 little, and then tapers nearly to a point ; the conical cavity in 

 its base is contracted ; and the cells produced on the inner 

 surface of the capsule contain no pigment. Still, for some 

 time, it continues thus to live and grow ; and the vigor of the 

 pulp lasts rather longer than that of the sheath or capsule, for 

 it continues to produce pigment-matter for the medullary sub- 

 stance of the hair after the cortical substance has become 

 white. Thus the column of dark medullary substance appears 

 paler and more slender, and perhaps interrupted, down to the 

 point of the conical pulp, which, though smaller, is still dis- 

 tinct, because of the pigment-cells covering its surface. 



At length the pulp can be no longer discerned, and un- 

 colored cells are alone produced, and maintain the latest 

 growth of the hair. With these it appears to grow yet some 

 further distance ; for traces of the elongation of their nuclei 

 into fibres appear in lines running from the inner surface of 

 the capsule inwards and along the surface of the hair ; and the 

 column of dark medullary substance ceases at some distance 

 above the lower end of the contracted hair-bulb. The end of 

 all is the complete closure of the conical cavity in which the 

 hair-pulp was lodged, the cessation of the production of new 

 cells from the inner surface of the capsule, and the detach- 

 ment of the hair, which, as a dead part, is separated and falls. 



Such is the life of a hair, and such its death ; which death 

 is spontaneous, independent of exercise, or of any mechanical 

 external force the natural termination of a certain period of 

 life. Yet, before the hair dies, provision is made for its suc- 

 cessor : for when its growth is failing, there appears below its 

 base a dark spot, the germ or young pulp of the new hair 



