SECT. 59.] 



HAIRS. 



109 



Fig. 47. 



I 



a stripe or cord extending in the axis of the hair from above the 

 Imlb to near the apex. This substance is generally wanting in 

 downy hairs, frequently also in the coloured hairs of the scalp; but 

 is, for the most part, present in the short and thick, as well as in 

 the stouter long hairs, and in white hairs of the head. By simply 

 boiling white hairs in caustic soda until they swell out and coil up, 

 the cellular structure of the medulla, now rendered transparent, 

 may be often seen by mere compression of the softened hairs, and 

 without further preparation. If such a hair be carefully teased 

 out, it is very easy to isolate the medullary cells, either connected 

 in rows, or even singly. They are rectangular or quadrangular, 

 seldom roundish or spindle-shaped, cells, of 0*007'" to 0.0 1'" in 

 diameter, here and there furnished with dark, fatty-looking gra- 

 nules; and, in many cases, when the alkali has not acted too 

 strongly, with a roundish, distinct clear spot, of 0001 6'" to o , oo2 / ", 

 which evidently represents the rudiment of a nucleus, and even 

 appears to swell up some- 

 what in soda. In the 

 fresh hair, the medulla 

 of the shaft is silver- 

 white or dark, which ap- 

 pearance, as many more 

 favourable objects show, 

 is produced by irregularly 

 roundish air vesicles, 

 which fill the medullary- 

 cells in large quantity — 

 black (opaque), or white 

 and shining, according to 

 the illumination. Their 

 nature can be readily 

 perceived, when a white hair is boiled in water or ether, or treated 

 with oil of turpentine, in both of which cases the rig 48. 

 medulla becomes quite clear and transparent. If 

 such a hair, treated with water, be dried between 

 the fingers, it regains quickly, often in a trice, and 



visibly to the naked eve, its former white colour; ceiis, with paie nu 

 . . . . . . clei ancl fatt >' R ra_ 



and if it is placed under the microscope immediately miles - finm » li:lii " 



1 - 1 , * treated with soda. 



after drying, without fluid, or with fluid only at one Magn. 350 times. 

 (iid, nothing is easier than to see the air re-entering, and the 

 medulla becoming dark again. Not only in white, but also in 

 coloured hairs, the medulla contains air when examined in the 

 fresh condition. 



A portion of the root of a dark hair, slightly acted upon by 

 caustic soda. a. Medulla, still containing air, and with cells, 

 which appear pretty distinct ; b. cortex with pigment spots ; c. 

 inner layer ot the epidermis ; d. outer layer of it ; e. inner 

 layer of the inner root-sheath {Huxley's layer) ; /. outer fenes- 

 trate! layer (Settle's layer). Magnified 250 times. 



Eight medullary 



