58 TRICIIOLOGIA MAMMALIUM; 



exerted, it flows or curls in the direction of one of these flattened sides, in exact proportion 

 to the eccentricity of the ellipse. An eccentrically elliptical filament of pile, being still 

 flatter, the spiral curl is the necessary consequence. 



Proofs. Every one knows how easy it is to bend a spatula, (which is fibrous,) in the 

 direction of either of its flattened surfaces, while his whole strength cannot make it bend 

 in either of the contrary directions. Just so it is, (except in an inferior degree,) with a 

 flattened hair ; a small degree of elastic force will cause it to flow towards one of its flat- 

 tened sides, and a little more will make it curl in the same direction; but no stretching 

 or shrinking force ever makes it flow or curl edgewise, or in the direction of its ellipse. 



From a piece of wood, (where the fibres acting conjointly preserve the whole mass 

 straight,) plane a thin shaving, and it will curl. It is the same force that preserves a 

 watch-spring in a spiral curl, while an equal quantity of metal, in a cylindrical form, will 

 be straight. Pass a cylindrical hair between rollers, flattening it, and it will flow, curl or 

 form spiral curls in proportion to the flattening. 



The Consequences. These laws being firmly established, we can judge of the direction 

 of pile by its shape, and of the shape of pile by the direction.* We will recur to this sub- 

 ject again directly. 



OF THE INCLINATION OF PILE OF THE HEAD. By the inclination of pile we mean the 

 angle which the filament forms with the tegument from which it proceeds. This inclina- 

 tion does not depend upon the shape, nor upon the direction ; nor does the direction 

 depend at all upon the inclination; but it is due entirely to the angle which the root of the 

 pile bears to the skin of the animal in which it is imbedded. 



The roots of cylindrical and oval pile have an acute angle of inclination; for which 

 reason those hairs do not grow out of the epidermis at a right angle thereto, but incline in 

 a determinate manner; while the roots of eccentrically elliptical pile lie in the dermis 

 perpendicularly, and hence the filaments pierce the epidermis at right angles thereto. 



Of particular inclinations of Pile. The foregoing description of the general inclination 

 of pile of the head is governed by the following subordinate rules, viz: 1st. That of the 

 anterior part of the cranium inclines obliquely in front, having a tendency to cover the 

 forehead, and that of the posterior and inferior portions obliquely, transverse, so as to make 

 the locks fall naturally along the posterior part of the neck ; it is the same with the sides 

 of the head, where the inclination carries this covering to the region of the ears. But 

 these inclinations are, sometimes, partially artificially altered. Bichat ventured the 

 opinion that these natural inclinations of the hair belong to the part of the bone which lies 

 underneath ; but of this we see no proof. The skull of the negro and that of the white 

 man, are composed of the same number of pieces. 



* It is true that sometimes the shrinking process of the two flattened sides alternate, when an exception, in the shape 

 of the undulating hair is the consequence ; but generally, if the shrinking force of the fibre on one flattened side of the 

 filament, gains the ascendancy over that of the other side, a curl in that direction is permanent ; for the more the former is 

 curved, the more force will be required for its recursion, and the more the latter is stretched, the less will be its power to 

 return to its original condition. 



