OU, A TREATISE ON PILE. 53 



which we cut transverse sectioiis or disks of pile, thereby completely obviating the diffi- 

 culty. 



Transverse Sections. Figure 57 A is a representation of such a transverse section of 

 the hair of the head of the Choctau- Indian. Figure 57 B is a representation of such a 

 transverse section of the hair of the head of his Excellency General Washington. 



The same difficulty does not exist to the same extent, in examining pile that is eccentrically 

 elliptical; for if a spiral curl of this description is placed between two pieces of glass, and 

 moderately pressed, a part of it will exhibit, under the microscope, the thin edge of the ellipse, 

 and another portion will represent one of the flattened sides. Figure 58 is a representation of 

 a single filament of a spiral curl of a pure negro head. 



OF DUCTILITY, FLEXIBILITY, ELASTICITY AND TENACITY OF PILE. Ductility is that 

 property of matter which allows of its being stretched or extended in length, iipon the appli- 

 cation of force or power, whether mechanically or chemically applied. Flexibility is that 

 which allows of its being bent, or moved in a lateral direction. Flexibility is always 

 accompanied by ductility on one side of the thing bent, and elasticity on the other side. 

 Elasticity is the spontaneous returning to its original dimensions and juxtaposition of its 

 particles, after the thing stretched or bent has been relieved from the force or chemical 

 action. It depends upon a law in regard to the natural arrangement of the particles of 

 matter, under which they exert a tendency to return to their normal juxtaposition, after 

 having been partially separated ; a tendency which pre-eminently distinguishes solids 

 from fluids; which latter, conform to no such law. Elasticity does not belong, exclusively, 

 to vitality; for it is traced to some minerals, as the elastic bitumen, &c., &c. It is found 

 in the fibres of some plants, and remains there after their vitality has been destroyed. 

 Tenacity is the adherence of the particles of matter, constituting strength. Tenacity may 

 be accompanied by ductility, flexibility and elasticity, or it may not. When it is, the 

 substance is said to be tough, when it is not, it is brittle. 



Essential Properties. Ductility, flexibility, elasticity and tenacity are the properties of 

 pile, with such few (if any) exceptions, that they are deemed to be essential. 



Of some supposed exceptions to the Rule. The properties of ductility, elasticity and 

 tenacity, are in the Jibrous portion of the filament of pile, as we stated in a previous 

 Chapter. 



It has been supposed that the hair of the three-toed Sloth (Brady pus tridactilis) is 

 destitute of ductility and elasticity, but it is so only in a degree; for one inch of the hair 

 of this animal, with 240 grains, stretched -! of an inch, showed a loss of elasticity of -^ 

 with 240 grains, and was fractured with a weight of 250 grains. The cortex is irregular 

 and inelastic ; separates into amorphous brittle pieces, but will not divide into fibrils. 

 Sometimes the shaft has deep fissures. The central portion is fibrous, the fibres having a 

 diameter of -%fa of an inch. (See ante, fig. 45.) 



The hairs of those animals that have a paved cortex bend at a right angle, remain in 

 that position, and also tie in a closed knot, (which is not the case with common hairs,) but 



