SUDDEN BLANCHING OF THE HAIR. 127 



marked in all the long hairs, as is seen on transverse section. 1 

 It forms from one-sixth to one-third of the diameter of the 

 hair. The medulla can be traced, under favorable circum- 

 stances, from just above the bulb to near the pointed extrem- 

 ity of the hairs. It is composed of small, rounded cells, from 

 20 * 0o to YsVir of an inch in diameter, nucleated, and fre- 

 quently containing dark granules of pigmentary matter. 

 Mixed with these cells are numerous air-globules ; and fre- 

 quently the cells are interrupted for a short distance and 

 the space is occupied with air. The dark granules of the 

 medullary cells are supposed by Kolliker to be merely globules 

 of air. 3 The medulla likewise contains a glutinous fluid 

 between the cells and surrounding the air-globules. 



Growth of the Hairs. Although not provided with 

 blood and deprived of sensibility, the hairs are connected 

 with vascular parts and are regularly nourished by imbi- 

 bition from the papillae. Each hair is first developed in a 

 closed sac, and at about the sixth month its pointed ex- 

 tremity perforates the epidermis. These first-formed hairs 

 are afterward shed, like the milk teeth, being pushed out, as 

 it were, by new hairs from below, which arise from a second 

 and more deeply-seated papilla. This shedding of the hairs, 

 which was first described by Kolliker, 8 usually takes place 

 from two to six months after birth. 



The difference in the color of the hair depends upon 

 differences in the quantity and the tint of the pigmentary 

 matter; and in old age, the hair becomes white or gray 

 from a blanching of the cortex and medulla. 



Sudden Blanching of the Hair. It is an interesting 

 question, in connection with the nutrition of the hair, to 

 examine the instances so often quoted of sudden blanching 

 of the hair from violent emotions or other causes. Some 



1 SAPPEY, Traite d 1 anatomie descriptive, Paris, 1852, tome ii., p. 600. 



2 KOLLIKER, Sandbitch der Gewebekhre des Menschen, Leipzig, 1867, S. 130. 



3 Op. tit., S. 137. 



