HAUL 



HAIUS. 



directly proportionate, and both attain their maximum in the crisp 

 woolly hairs of the negro, which are sometimes as much as two-thirds 

 broader in one direction than in the other. The hair of the negro 

 however, though called woolly, differs considerably from the wool, 

 properly so -named, of sheep and other animals : the latter is not 

 :!y curled, but wavy, all its curves being nearly in the same 

 plane ; it is much more deK ! perfectly round, and hence, 



from its being equally fitted to curl in any direction, is peculiarly 

 adapted for spiunintr, while the flattened hairs of men have always a 

 tendency to turn their broadest surfaces towards the middle of the curl. 



Except at their base, into which the conical pulp enters to a 

 variable distance, the hairs are perfectly solid, and in most animals 

 their substance is similar throughout. Weber has shown that the 

 appearance of a central canal running along them, and of a softer 

 internal than external material, has resulted from microscopic errors, 

 occasioned by the unequal refraction of light passing through their 

 rounded or grooved surfaces. Only in the lion, zebra, and llama, did 

 Weber find that the internal part seemed rather paler than the outer ; 

 in the roebuck and a few other animals he found the cellular structure 

 !i has been sometimes erroneously supposed to exist in all hair. 

 The cells are all hexagonal, much like those in the cellular tissue of 

 plants. The average diameter of hairs from the human head are 

 lively about l-300th and l-500th of an inch, and hairs often 

 attain a length of 6 or 7 feet in women. Instances are recorded also 

 of the hair of the beard growing to a length of 9 feet. They are 

 generally of the same thickness throughout their whole length in 

 man, but in the finer kinds of wool they are of unequal size 

 at different j,.u-ts. This seems to indicate an occasional alter- 

 ation in the size or activity of the pulp, a supposition which is 

 further supported by the varieties of colour which the same hair 

 1 irnea presents, aa in those animals which seem to have gray furs, 

 but in which each hair is made up of alternate bands of black and 

 white. In man however nothing of this kind occurs ; the colour of 

 each hair is uniform, the appearance of grayuess being produced by a 

 mixture of completely white with dark hairs. The colour of the 

 human hair generally varies with the colour of the iris and the general 

 dark or light hue of the skin. Commonly, the darker the hair the 

 more robust the body, and the coarser the skin and other tissues ; 

 and this holds still more with animals than in man, for not only 

 are white or gray horses less healthy and vigorous than dark ones, 

 but if one or two of a dark horse's legs be white they are always 

 inure liable to injury and to disease. 



Hairs are capable of movement, and the standing of the hair on 



end from alarm is not imaginary. It is found that each bulb of the 



hair is supplied with a minute miincle, which acts in producing move- 



l the hair. (Lister, On the Muscular Tissue of the Skin, 



' Micro.-iu.iiiio.al Journal,' vol. i. p. . 



Haii-Hare very elastic; they admit of being stretched nearly one- 

 third of their length, and regain their original length almost com- 

 pletely : in proportion to their size they are very tough and firm. In 

 masses they are impenetrable, except to very great violence, and 

 hence one of their uses in the thick coverings of animals ; they are 

 also adopted in armour, as for the coverings of helmets. They are 

 extremely bad conductors of heat, and they are generally found most 

 thick and abundant in animals subject to long exposure to oold, in 

 whom moreover an additionally thick coat is provided at each winter 

 the annual shedding. They are non-conductors of electricity, 

 and when rubbed with almost any other substance so large a quantity 

 of negative electricity is developed that in the dark even sparks may 

 11, and the peculiar crepitating sound of rapid little electrical 

 discharges may be heard. This is especially the case with- the drier 

 hairs of cats, dogs, &c. ; but the weaker electrical phenomena may be 

 observed by nibbing the human scalp. Hair is also remarkably 

 -hygrometric, attracting and retaining in its tissue a large quantity of 

 '[iicnceof which it becomes flaccid ami lengthens, 

 and hence it is used in the construction of the more common hygro- 

 s also to shield the skin from moisture by its oily 

 surface, and when thick presents almost an impenetrable barrier to 

 wat r. Thus serving to isolate the animal from the three most 

 : l'ul external agents, heat, electricity, and moisture, it is scarcely 

 possible to imagine, any structure better adapted for the external 

 ng of the whole body, whose motions it is too light to impede, 

 and to whose beauty it so remarkably contributes. 



In chemical properties hair resembles horn, nails, &c. It is soluble 



r at a. very high temperature, as in a Papin's digestor, leaving 



a largo quantity of oil mixed with sulphuret of iron, and some 



uretted hydrogen. It is this oil, with tho sulphuret of iron, 



t <y hair depends. These are all composed of some 



w't "' mixed with some oily or fatty substance 



in tli' "inatum, insinuates itself into the hair, where it is 



a black Hiilphuret of silver or lead is formed. Hair 



. alkalies and alkaline earths, and t 



W are uhielly composed of quick-lime, which 



' r U materially injurious to the skin at the name time that it 



removes the hair. Hair contains a very suiall quantity of water, and 



when burnt leaves a large proportion of ashes, containing iron, 

 manganese, and various salts of lime ; it is owing to these properties 

 that hair is peculiarly indestructible, and has been found unaltered on 

 mummies more than twenty centuries old. It has even been supposed 

 to grow after death, but it is probable that, in the few authentic 

 cases in which this is stated, it was owing to the lengthening of the 

 hair by the attraction of moisture from the body or surrounding 

 atmosphere, and to the more rapid drying and contraction of the 

 adjacent tissues. 



Little need be said of the diseases of hairs. Possessing neither 

 vessels nor nerves, except at their base, they are rarely altered except 

 by the diseases of the skin itself. [ENTOPHYTA.] Their fall, as it is 

 called, is in most animals annual, but in man seems not to occur 

 except by accident, or after particular diseases. The process by which 

 it takes place is unknown, but is probably similar to that of the 

 shooting of the quills of the porcupine, by the gradual approximation 

 of the base of the follicle to the surface. Their loss of colour, which 

 is sometimes exceedingly rapid, is owing to deficient secretion of the 

 colouring oil, and can only, very rarely be remedied. When sufficient 

 moisture is not supplied they sometimes split at their points like 

 bristles ; at others they break at the middle of the shaft, snapping off, 

 and leaving a little fringed extremity to the stump. The most 

 singular alteration however to which they are subject is that called 

 the ' plica polonica,' from its occurring almost exclusively in pome 

 towns in Poland, in which, with so much general disease as sometimes 

 proves fatal, the hair of the head becomes sticky and matted together, 

 when touched gives extreme pain, and is sometimes said even to bleed 

 when cut. This fact cannot however be regarded as evidence of the 

 hair naturally containing vessels, though it indicates an elongation 

 of the pulp to some distance beyond the skin, just as is the case in 

 dogs, whose whiskers will sometimes bleed if cut very close to the 

 surface. [SKIN.] 



(\Veber, in Hildebrandt's Anatomic, vol i. ; Gurlt, in Miiller's 

 fiii- Anatomic mtd Physioloyie, 1835; Kolliker, Manual uf 

 //union ffittoloyy, translated by Busk and Huxley for Sydeuham 

 Society.) 



HAIKBELL. [CAMPANULA.] 



HAIR-GRASS. [AIHA.] 



HAIRS. In plants these are long expansions of the cuticle, chiefly 

 intended to answer the double purpose of collecting moisture from the 

 atmosphere and of protecting the surface of a plant from the too 

 powerful influence of the sun's rays. It is supposed that they are 

 also destined to assist in the conveyance of certain kinds of seeds 

 through the air, and in other cases, as in that of cotton, they are 

 specially adapted for the use of man. That the two first purposes are 

 those for which hairs growing on the surface of plants are intended, 

 seems sufficiently indicated by the following facts : 



, common hairs of the stem of Bryonia alba t becoming glandular at the base 

 or apex; 2, 3, a mixture of hairs (2) and glands (3) from the stem of Dic- 

 tnmnia ; 4, double glands at the point nf the hairs of f.'/\iin:n'!:ni I'ltlyaris ; 

 5, a hair glandular at the apex, from Primula Sincniis ; 6, gland O n the end of 

 the hairs of Sisyinbriitm Su/thiu ; 7, one of the yellow glands found on the head 

 of the hairs of Scrophularia nodoaa, 



In all cases hairs are composed of lengthened cells of cellular tissue, 

 extending from one or more of the cells of the cuticle. Most com- 

 monly they are quite simple, and are merely formed of several cells 

 of equally diminishing size, placed end to end, or of a single cell. Of 

 the latter kind are the long entangled hairs that clothe the surface of 

 the cotton-seed, and which are manufactured into thread and linen. 



