HAIR. 



[ 378 ] 



HAIRS. 



each midrib being terminated below by a 

 little knob. 



The examination of the hair and its dis- 

 section can only be effected by the aid of 

 chemical reagents, especially sulphuric acid, 

 solution of potash or of soda. These should 

 first be used cold ; and if no separation of 

 the components ensues, heat even to boiling 

 must be applied ; the subsequent addition of 

 water is sometimes advantageous. Sections 

 of hair can be made with a razor, a bundle 

 of hair being fixed between two flat pieces 

 of cork, or between two cards. Transverse 

 sections of the human hair can be obtained 

 by shaving a second time, an hour or two 

 after the first ; the sections should then be 

 washed in water. The cortical cells are 

 most beautifully seen in white hairs which 

 have been thoroughly soaked in oil of tur- 

 pentine, and mounted in Canada balsam. 

 The air-cells of the medulla are best ob- 

 served in hairs which have been mounted 

 in balsam without the previous application 

 of turpentine. The sheaths of the hair 

 keep best in solution of chloride of calcium 

 or glycerine. 



Many of the structures of the hair of the 

 Mammalia may be well observed in the 

 large hairs or bristles (whiskers) of the ox, 

 &c. ; in these also the pulp is seen to contain 

 blood-vessels, which have not been detected 

 with certainty in that of man. They also 

 exhibit bands of smooth muscular fibres, 

 arising from the cutis, descending through 

 the hair-follicles, and terminating below 

 the sebaceous follicles, forming the erectores 

 pili. 



The hairs of some animals polarize light. 

 An interesting object of this kind may be 

 made by placing two series of the white 

 hair of a horse in balsam, so as to cross 

 each other at an angle, and viewing them 

 by polarized light (PL SO.^fig. 39). 



In regard to the discrimination of the 

 hairs of one animal from those of another, 

 we believe that the examination of indi- 

 vidual hairs can in general be but little 

 depended upon; whilst a comparison of 

 their form, length, and breadth, with the 

 proportion of the true hair to that of the 

 wool, conjoined with the consideration -of 

 the internal structure, may often enable 

 an observer to arrive at a satisfactory con- 

 clusion. 



BIBL. Kolliker, Mikr. : Eble, Haare in 

 d. gesammt. organ. Natur ; Henle, Allg. An. ; 

 Todd & Bowman, Phys. of Man ; Erdl, 

 Miinchen. Ahh. Bd. iii. ; Huxley, Med. Gaz. 



1845; Griffith, ibid. 1848, 844; Heusinger, 

 Histol. ; Gurlt, Mull. Archiv, 1836 ; Aikin, 

 Arts and Manuf. ; Bonders, Mulder's Phy- 

 siol. Chem.-, De Morgan, Phil. Tr. 1859 

 (Crustacea); Pfaff, D. mensch. Haar. in 

 phys., pathol, $ forens. Bedeut. 1869 ; 

 Goette, Schnitzel Archiv, 1868, 273 ; Bie- 

 siadecki, Strieker's Handb. 600 ; Hofmann. 

 M. M. Jn. 1873, 167 ; Frey, Histolog. 1876, 

 419 ; Sorby, Jn. Linn. Soc. 1881, xv. 337. 



HAIRS OF PLANTS, trichomata or tri- 

 chomes. The term hair is applied in botany 

 to filamentous productions upon the surface 

 of the organs of plants, consisting of one 

 or more cells arising out of and constituting 

 part of the epidermal structure. Hairs of 

 plants present a great variety of conditions : 

 in the simplest kind those "composed of a 

 simple, cylindrical, conical, bifurcated or 

 stellate cell they may be varied in form 

 by the peculiar shape of the constituent 

 cell, in individual character by the presence 

 or absence of special secretions in the cell- 

 cavities, and in their collective character by 

 the mode of arrangement on the epidermis, 

 since they may be few and scattered, or so 

 numerous as to form a velvety coat. Com- 

 pound hairs, namely those composed of a 

 number of cells, vary in like manner, and, 

 moreover, in the examples where the cell- 

 walls acquire considerable thickness, pass 

 gradually from pure hairs into bristles, and 

 thence into the structures called THOBNS 

 (distinguished from true spines by being 

 appendages of the epidermis). The stellate 

 forms also present many variations inter- 

 mediate between hairs proper and SCALES. 



These structures are interesting to tha 

 microscopist on account of the variety and 

 often extreme elegance or curiosity of their 

 forms. They likewise strongly attract the 

 attention of the physiologist from the sim- 

 plicity of their organization and their free 

 condition, allowing the phenomena pre- 

 sented by the cell-contents to be readily 

 observed under the microscope. In reference 

 to their characters as microscopic objects, 

 it will suffice to indicate their principal 

 modifications, and state a certain number 

 of examples. For this purpose they may 

 be classified as follows : 



Simple hairs: unbranched, Cabbage-leaf 

 (Brassica, fig. 304), (Enothera, Dictamnus 

 (PI. 28. fig. 39 ), Anchusa (fig. 17) ; bifur- 

 cated, Capsella (fig. 36), Draba (fig. 307) ; 

 inflated or capitate, Antirrhinum (fig. 306 

 and PI. 28. fig. 34), Salvia (fig. 305), Helle- 

 borusfostidus ; branched, in many Crucif era>, 



