186 TEXTILE FIBRES. 



burn so readily, but jrizzJes when in contact with a flame. Accord- 

 ing to Dr. E. J. Mills, F.R.S., the chemical formula for wool is 

 C 42 H 157 N 5 S0 15 ; that for cotton being C 6 H 10 5 ; and that for silk, 



c*H.N|Og. 



Wool that is shorn from the sheep while living is generally termed 

 the " fleece wool." It has better felting properties than that obtained from 

 the sheepskin after life becomes extinct. In the latter case it is often 

 spoken of as " dead wool." 



Human Hair. The hairs on the human head are epidermal coverings 

 to the skin of the head. They originate in a cutaneous depression, the 

 hair follicle or bag. These hairs are not tubular structures. 



The conspicuous feature of hair is the shaft or scape of the hair 

 emanating from a bulb or root in the deep, depressed follicle of the 

 hair. When a hair is plucked suddenly from the scalp, the bulbous 

 part may readily be distinguished by the aid of a Coddington lens. 



A single hair examined under the microscope by transmitted light 

 shows a medullary sheath, or pith, an outer part termed the cortex, 

 or fibrous portion, which constitutes the bulk of the hair proper. 

 When treated with reagents the fibres become separated into cells, 

 showing some fibrillation and nucleated structure. 



In coloured hairs pigment granules about -^$^$-3 inch in diameter are 

 met with. Of hair in a natural state, the chief differences between 

 that of man and of the lower animals in general are (a) the size; 

 (b) the relative proportions of the cortical and medullary structures; (c) 

 the seat of the pigment cells; (d) the position of the medullary cells; 

 (e) the amount of tomentose down, hair, or wool; and (/) the size of 

 the superficial cortical cells or scales, upon which the felting property 

 depends. 



Fibres, Cultivation and Variation, The Character of the breed and 

 the pasturage that is afforded to the animals have an important bearing on 

 the wool fibres of commerce and the structural characteristics of wool 

 produced on the different parts of the body. Tho uniformity of length 

 and of diameter, and the number of scales per inch, vary in different 

 individuals, even among the same breed of sheep. On this subject 

 Mr. N. Burgess, of the Quekett Microscopical Club, says : " The size 

 of the fibre is very irregular, scarcely any two forms in the same staple 

 being found alike, and each varying in its own length. 



"In a fibre of Southdown wool, a comparatively uniform species, 

 I have found the size to vary in ^^ f au ^ nca as muca as one-fifth 

 of the whole diameter. The finest Saxon wool I have ever seen gave 

 a remarkable result on being measured. Five hairs in one staple were 

 selected. The finest gave the extremely small diameter of ^jVy f an i ncn 



