OR, A TREATISE ON PILE. 53 
which we cut transverse sections or disks of pile, thereby completely obviating the diffh- 
culty. 
Transverse Sections —Figure 57 A is a representation of such a transverse section of 
the hair of the head of the Choctaw 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 arepresentation of 
a single filament of a spiral curl of a pure negro head. 
Or Ductiniry, Fuexipiiry, Exvasticrry anp Tenacity or Pite.—Ductility is that 
property of matter which allows of its being stretched or extended in length, upon the appli- 
cation of force or power, whether mechanically or chemically applied. Flexibility is that 
which allows of its being dent, or moved in a lateral direction. Flexibility is always 
accompanied by ductility on one side of the thing bent, and elusticity 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 ¢s, the 
substance is said to be tough, when it zs 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 essentzal. 
Of some supposed exceptions to the Rule-——The properties of ductility, elasticity and 
tenacity, are in the fidrous 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 (Bradypus 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 12 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 ,1, 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 
