1 18 



HAIRS. 



[sect. 65. 



twenty-third to the twenty-fifth week, are short fine hairs, whose peculiar 

 disposition has been mentioned above. They measure at the bulb, o-oi'" ; in 

 the shaft, 0-006'" ; at the point, 0-0012'" to 0-002'". They are light-blond, 

 or almost colourless, and consist only of fibrous substance and cuticle. The 

 bulb, in man, is generally colourless, and rests upon a very distinct papilla, 

 which arises, as usual, from the bottom of the hair-follicle. This has the 

 same three layers as in the adult, and a very well developed epidermic lining, 

 viz., an external root-sheath of 0-004'" to 0-012'", and an internal root-sheath 

 of 0-006"' to 0-008"', without apertures. 



After their eruption, the downy hairs continue to grow slowly to a length 

 of j to I of a line, and to a greater length on the head than in other parts. 

 The majority remain to the end of foetal life, and become gradually darker ; 

 in many case3, as on the head, even blackish ; whilst a very small portion fall 

 off into the liquor amnii, along with which they are often swallowed by the 

 foetus, and are then found in the meconium. A proper shedding of the hairs 

 does not, as far as I can see, take place at all during embryonic life, and the 

 infant is born with the lanugo ; nor is there any trace to be seen of a further 

 formation of hair-rudiments after the complete eruption of the lanugo. 



Fig. 53. 



§ 65. Shedding of the Hair. — After birth, a total shedding of 



the hair takes place, by new hairs 

 arising in the follicles of the downy 

 hairs, and gradually displacing the 

 old ones. This shedding of the hairs, 

 "which I discovered in the eyelashes 

 of a child one year old, is caused by 

 an increased growth of the soft 

 round cells of the hair-bulb, and of 

 the adjoining outer root-sheath at 

 the bottom of the follicle of the old 

 hair, whereby there is produced an 

 elongated process or mass of cells, 

 which is interposed between the hair 

 and its papilla, so that the hair be- 

 comes detached from the latter, and 

 is, at the same time, also hardened 

 or cornified in its lowest part. When 

 the above-mentioned process has at- 

 tained a length of 025'" (fig. 53, A.), 

 a differentiation of its external and 

 internal cells takes place, similar to 

 that which was described above 



Hairs of the eyelashes of a child, one year 

 old ; magnified 20 times. A. With a process 

 of the bulb or external root-sheath, of 025'" 

 in length, in which the central cells are elon- 

 gated (their pigment is not here represented), 

 and distinctly marked off from the outer 

 ones in the form of a cone. B. With a 

 process, of 03'" in length, in which the inner 

 cone is transformed into a hair and an inner 

 root-sheath. The old hair has moved further 

 upwards, and like as in A, is devoid of an 

 inner root-sheath, a. Outer; b. inner root- i-i -, • r-.i •• n 1 



sheath of the young hair ; c. hair-cells of the Willie Speaking Ot the Origin 01 the 

 papilla?; d. bulb; e. shaft of the old hair; -\ i • • ., ,, , -,. 



/. bulb; g. shaft; h. point of the young hair; UOWliy Iiail'S 111 their Cellular l'Udl- 

 i. sebaceous glands; k. three sudoriparous . Titri - i , -\ , 1 , 



ducts, which in A. open into the upper part of meiltS. W llllst, namely, the Outer 

 the hair-follicle ;/. transition of the outer root- n • i i n i 



sheath into the mucous layer of the epidermis. Cells remain l'OUlld and Colourless, 



