HATR. 



[ 312 ] 



HAIRS. 



broader, the spines remaining as midribs, 

 whilst the margins are more developed, the 

 whole resembling a flower with four or five 

 petals ; but at the end of the hair, the scales 

 are longer, narrower, and recurved, 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 turpentine, 

 and mounted in Canada balsam. The air- 

 cells of the medulla are best observed in 

 hairs which have been mounted in balsam 

 without the previous application of turpen- 

 tine. The sheaths of the hair keep best in 

 solution of chloride of calcium. 



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. 



The hairs of some animals polarize light. 

 An interesting object of this kind may be 

 made by placing two series of the white 

 hairs of a horse in balsam, so as to cross 

 each other at an angle, and viewing them 

 by polarized light (PI. 31. fig. 39). 



In regard to the discrimination of the 

 hairs of one animal from those of another, 

 we believe that the examination of individual 

 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 struc- 

 ture, might sometimes enable an observer to 

 arrive at a satisfactory conclusion. 



BIBL. Kolliker, Mikrosk. Anat. i.; Eble, 

 Die Lehre v. d. Haar. in d. gesammt. orga- 

 nisch. Nature Henle, Allgem. Anat., and 

 Fror. Notiz. 1840; Todd & Bowman, Phys. 

 of Man; Erdl, Abh. d. Akad. in Miinchen, 

 Bd. iii. ; Paget, Brit, and For. Med. Rev. 



1842, &c.; Huxley, Med. Gaz. 1845; Grif- 

 fith, Med. Gaz. 1848; Heusinger, System 

 d. Histologies Gurlt, Mull. Archiv, 1836; 

 Aikin, Arts and Manufactures; Donders, 

 Mulder's Physiologische Chemie. 



HAIRS, OF PLANTS. 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, co- 

 nical, bifurcated or stellate cell, they may be 

 varied inform 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 vel- 

 vety coat. Compound 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 THORNS (distinguished from true 

 spines by being appendages of the epider- 

 mis). The stellate forms also present many 

 variations intermediate between hairs proper, 

 and SCALES. 



These structures are interesting to the 

 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 ob- 

 served under the microscope. In reference 

 to their characters as microscopic objects, it 

 will suffice to indicate their principal modi- 

 fications, and state a certain number of ex- 

 amples. For this purpose they may be 

 classified as follows : 



Simple hairs : unbranched. Cabbage-leaf 

 (Brassica, fig. 308), (Enothera, Dictamnus 

 (PL 21. fig. 39 a), Anchusa (PI. 21. fig. 17) ; 

 bifurcated, Capsella (PI. 21. fig. 36), Draba 

 (fig. 311); inflated or capitate, Antirrhinum 

 (fig. 310 and PL 21. fig. 34), Salvia (fig. 309) ; 

 Helleborus fcetidus ; branched, in many Cru- 

 ciferae, as Sisymbrium Sophia (PL 21. fig. 35), 

 Alternanthera axillaris (PL 21. fig. 37); 

 stellate, Alyssum (fig. 312). Very often hairs 

 composed of a single cell are supported upon 

 a short cell, and then developed horizontally 



