LESSON 26.] 



HAIR. 



81 



FIG. 123. 



magnified 250 diameters ; a, nucleated cells of the medulla, without 

 air ; b, cortical substance, with distinct nuclei ; c, cutic- 

 ular covering, showing the imbrications. 



433. To demonstrate the presence of air in the me- 

 dullary cylinder, another illustration is necessary (Fig. 

 123) ; .the most conspicuous object is the bulb (a), in 

 which a dense aggregation of pigment cells is shown. 

 From this point the medulla remains intact to b, where 

 air is firstly found dividing the medulla ; thence we see 

 the frequent interruption of the medulla by the interven- 

 tion of air, until it ceases near the point, c. The original 

 specimen was a hair from the human eye-brow. 



434. The whole of these facts, however, may be seen 

 with advantage by consulting thin transverse sections of 

 human hair (Fig. 124). 



435. Here the cuticle (a), the cortical substance (b)j 

 and medulla (c), with its pigment cells, are well shown ; 

 the other figure (Fig. 125) was devoid of medullary pig- 

 ment cells, at the point where the section was made. 



436. The human hair is very elastic; it has been 

 found by experiment that it will stretch to more than 

 one-third its length without breaking. It readily im- 

 bibes water, and as readily gives it out again ; consequent- 

 ly, it is sometimes dry and brittle, sometimes moist 

 and soft, according as the skin, or the atmosphere, con- 

 tains much or little moisture. Moreover, it becomes 



longer or shorter, according to the quantity of moisture it contains. 



437. The chemical composition of hair has not yet been satisfac- 



Human eye- 



dulla - 



FIG. 124. 



FIG. 125. 



Transverse section, Human hair. 



Transverse section, Human hair. 



torily determined ; some authors suppose it to consist of a combina- 

 tion of proteine and sulphur, to which others add a small quantity 

 of a peculiar substance allied to gelatin. Hairs withstand putrefac- 

 tion better and longer than any other part of the body ; the hair of 

 mummies is always found to be quite perfect, 

 6 



