Section IV, (Part 1)

Section IV, op TUB SEIlACROt]» KOLLICLKS. TiiKSK minute liodieE appear to l>e formed of culs di! sac, which are principally placed on the external surface of tho cutis, and are lined by processes of the cuticle. Many anatomists are of an oppusitu opinion, and con- tend that they are distinct grinds. This opinion is sup- ported by Mr. Chevalier, who states that there are two orders of seliacfous glands ; one set being parliall)' or entirely imbedded in the corium, and the other, which is less known, lying between the rete inucosum and the cuticle. The latter may be soen adhering to the internal surface of thf cuticle, after a maceration of several weeks, which will cause the rete mucosum to be .so much de- composed that it may be washed or nibbed off. The mouths, or ducts of these little follicles, which opi'O obliquely on the cuticle, are very apparent on the nose, in consequence of their greater siise ; they are also seen on the edges of the eyelids, on tbL> cheeks, on tba nipple, in the axilla, around the anus, Sec. The arrangement of the sebaceous glands varies ac- cording to their situation. On the palmar surface of the thumb and fingers, they arc disposed in rows, which correspond with the linear projections seen on the exte- rior ; in other parts of the body there is no regular order observed in thuir disposition. We learn from the i 214 eHBACSOUS SICBKTION. stiitcmonl of Mr. Che^-alier, that the number of thpf^ bodies is almost incredible ; in one of his preparatinnit deposited in the museum of the College of Surgeons, no less than one hundred and thirty of them may be counted with the naked eye in the surface of ^ part of a fiqui inch.* The follicles of the skin are provided for its defence ngainst the influence of the air and moisture. They Crete an unctuous matter of a whitish colour, which con- ' stanlly bedews the externa] surface, so as to prescnc the softness and smoothucss which are required for the pro pcr exerdtie of the cutaneou!) functions. This secretin repeU aqueous fluids, as we readily observe when the hand or other part of the body is placed in water ; it also prevents, in a great d^^ee, tlie effects of fricdon ; this is evidenced in the onnpit, which is so frequently ndibt^fl in the movements of tiic upper extremity. The eebacenus nvatter frequently accumulates in ducts, from whence it may be scjueezed out in the for of small wormn, of a yellowish colour, and dork on the ends, so OK to look like heads. It is not suluUe ii water, although it may be mixed with it, so as to for a kind of emulsion. It is not readily inflammable, l>ut it burns and leaves in its residue a quantity of chare It appears to consist principally of ceraceous and oleM ginous particles. It is necessary to odd, that tlie set lion of the sebaceous glondji is totally distinct from matter of perspiration. This is illuKtrated by the simptej experimcnl of placing the end of the thumb or finger,] moderately heated, on a polished mirror, when it iaj always found that the stain of Uie perspiration is left QB.J * 8k I^ctum. I'UtttS. 4,miS. or THE HMM. the glass cverj-where, except at the orilices of these fol- licles, proving that they cannot be the source of the vapour which is exhaled. S&CTIOM V. OF THE AI'PENDAOlS OF THB SKIN. In the preceding pugbs the structure of the skio has been examined j but in order to render the description of that organ complete, it is retjuisite to consider it^i ap- pendages, which consist, in the Imman species, of the hairs and the nails. lo animals, many other productions are observed, such as horns, feathers, scales, &c. OF TUB II.\IKS. The hairs, culled, according to their situation and size, pili, erinea, barba, eapUU, capilluti, &c. are homy filaments placed on the exterior of the body, and which are intimately connected with all the layers of tlie skin, and not merely nHth the epidermis, as some auatomists have erroneously supposed. In man the large hairs ore confined to certain parts, whilst in quadrupeds they ex> tend over tlic entire surface. It must be noticed, how- ever, that all parts of the body, excepting the palm of the hand and sole of the foot, are covered by minute hairs, constituting the pubescence or down ; a fact wliich justifies the observation of Haller, that man is naturally a hairy animal, aud that the face of the most delicate woman is entirely covered with hair. The head is the principal seat of the hairs. On the scalp they are vtiy numerous, long, and strong ; the length of these hairs !»LC SITUATION, COLOUB. u xonoetiioes bo great, that they reach Unraitb the bwtr pirt uf tiio body. The ej-ebrows and erdubes, which are dutUuguuiicd by their curved form and <firectioo, «rc itnpUnted aroutxl the eyes, Ix-in^ proAided for tbe dfr fuucc of thoK organs against the eotrauce of foragn MibiitaQces. The orifices of the cofitrils, and, in a less dvgree, those of the ear, arc defended by some hain whick are lodged in the beginuing of their rcs{>ectivtr passages. Tlie clieekft, the iips, and chin, are uccupieU, in thC' muk aAiT pui>crty, by the beard, tJie extent and strength of which are liable to great variation. The hairs of thft trunk and limbs are not so numerous nor »o cotuOa/t as those of the head, with the exception of those mr*' rounding the orgaxis of generation, which arc always: developed at tlie period of puberty. Tlw unnpits are provided with boirti, which are seldom deficient; the an- terior part of the body possesses mure hair than the pcMterior port, and the lower extremities are better fiir- niHhed with it than the superior. The hair is confined on tlie hands and fuet to tbotr dorsal surficest the ab- itenoe of it in the op^xMiite direction being aubsernsQt tO> the perfection r)f the »ense of touch. The development of the hair in grmtly intloeooed by tho organs of generation ; thus the t>eard in the mole does not make its appearance till the time of puberty ; and if the testes are removed, as in eunuchs, or are not properly formed, the beard is luually weak ; it is also N«cn that in the boy the Uinbs are merely covered with down. In the femjde, the hair of the head does not attain its full growth till the same epoch ; and in both xcxes tlic gcnitaltt are tilt then defective in their covering, Tlie colour of tlie liair has n cloiie relation with that of the skin, luid, consetiuently, t!xhibil« tike it, iiiau- BULB AND ROOT. 217 mcniblf Kiindcs ; it U of a bruwo or red cok>ur in feir persons, unrl black in the dark rac«s of mankind. In the Aibiiio it is of a milky wbitenews ; and in those Negroes who have a spotted skin, the hair h white or black, according to the colour of the patches it covers. It 18 probable that the colouring matter is deri-cd from the vessels which pnss into the hair itself, for it cannot be furnished by the root, which is nlway:* white, whnt- evw may be the colour of the hair ; nor can it proceed from the rete mucosum, e^'en supposing that this covers the littir, which is not satif>factorily ajicerlaJncd. because the colour of the rcte is not always the same m that of the hair, which must have been the ciuse if thu shade of the latter was derived from the former. Each hair consists of a root plftced under the skin, and of a stalk which projects beyond the external sur- face. The root is contained in a bulb, which is situated in die subcutaneous cellular tissue or in the cutis vera ; it is ofn conical shape, the large end being connected with the skin and the fimaU end with the cellular ttxturc. The hulb, or as it Is also called the follicle of the hair, has been minutely described, especially by Chirac and Gordon. It is formed externally of a cap»idar membrane, which is whitish, and appears to be derived from the corium. Within it tlicre is another and more delicate membrane, containing a conical papilla, which ts received into the root of the hair. Sanguineous ve'tsels, and, ac- cording to some anatomists, even nerves may be traced to this papilla. The root of the hair is always whitislt and semitronsparent, whatever may be the colour of the stalk. It ui soft, and the lower part, which is al- most fluid, is rather hollowed to receive the papilla, on wliicb it rests. The stalk, or the part that projects be- S18 COMPOttlTIOH. yond the skin, is conical ; it grndually tApers from root to the point, and is often split into two, towa the extremity. Immediately nfter leading the bulb, the hair is received into a canal of the cutis, which is always mor« or less oblifiiic. The connexion between the hair and the «pi- dermis is not so sntislactorily ascertained. Many ana- tomists think that the cuticle, and also the rete mucosum, fiiniifih B sheath to the hiiir ; but others deny this, and contend ibat the epidermis is perforated. The former opinion is probably correct, because there is a g^rcat resemblance in tlie characters of hair and cuticle ; and when the Idtter is separated by putrefaction from the cutis, most of the hairs, owing to the iutiuiate uoioo with it, are also detached. The hair, when it is seen through the microscope, op* pears to be semi transparent, and to have a central dork- coloured canal, which is filled by a peculiar substance. It is said, that there is an external jiornr sheath ; and that ft number of tilaments, varying from five to ten, are contjiined within it ; but I have not myself been able to detetrt such appearances. It is generally thought that the hair, which grows froca the organized bulb, is in itself non-vascidur ; but an op- poaiti" opinion has been supported by some writers, with whom I am inclined to ugrec, although, it must be ad- mitted, that no vessels have been sati^^factorily derooo- strated. The deposition of the colouring matter, an^H the sudden changes which have been known to occur iff^^ the hair from the effects of meutrU emotion ;* and even * Muiy intliMxa oocunel iluting the borron or tin French Rn-i>luiioii, c< llie hRir (urntng ^jr in Iho count of a tew dap. Hod rtib change liu trto taken plaoo id m MDtcle nlg;h4. PR0PERT1K8 AND DBVBLOPMBNT. from excessive voncry, seem lo prove the cxiBtenoe of DUtritiuiu; arterkfi. It U almost needless to add, that if any vesseLs pass to tlie iiairs, they are extremely small, Bnd certainly would not Meed, as some persons have iuiHgined tliey do, when divided in the disease cdUud piica poUmica. The hairs, which arc apparently destitute of iicrvea, are quite inncnKiblc. A curious case of ptirenitiii, how- ever, is quoted by Dr. Elliotson, in which the hair wa* so sensible, that the sligtitest touch gave severe pain ; and when the surg;eon clipped n hair unseen by the patient, this wus inHtontly felt, and occasioned a paroxysm of rage. The hairs arc firot seen in the fo:tus towardN the mid- dle of pregnane)' ; they consist, at that period, of glo- bules which are placed under the external surface of the body. Tliey afterwards are elongated, and then they ap- pear on the skin in the form of a very flne and colourless down, the larger part of which is detached at the eighth month of gestation, and the remainder soon after birth. The hairs of the head, the eyvbrows, and the cilia, begin to appear about the fifth month ; but they are very deli- cate, and imperfectly coloured at the time of birth. We learn from Vauquelin, to whom we are indebted for an analysis of hair, that it consists principally of an animal matter united to a portion of oil. He states that the former is a species of mucus ; but ftfr. Hatchett has ascertained that it is chiefly albumen united to a ftmnll quantity of jelly, the proportion of which varies. This distinguishc«d chemist concludes from many experiments, that the hair which loses its curl in moist weather, and which is the softest and most flexible, is that which most readily yields gelatine, on boiling; while that which is eso OWtat ttAltS: very strong nod clastic, BfTords it with the gnatcat eulty, and in the (im!illt-:«t propurtioo. Tbc cokmriB^ nutttvr s)i|>ean to consist of an oily MibKtance united to a smiill portion of iron and fnilphur ; this oil ia Midi wiivQ thv liair employed is dark, and yeOnwlsh red frnn mi hair. Vautjuvlin obsL-rvwi, thai hair yielded, by in- cineration, iron and nrnn^neac Imparting a brownish yellow colour t« iht a«h<!s ; phospKate, sulphate, and carlMnatc of lime ; a little of the miirinte of soda, «nd a conniiicriiMi: |Mrcion of itilica. When hair is tbm burnt, it exhales a Ftmelt like that of the i-pidiTmitt, mad in other rcapecu it has a close rtecmblnncc lo tliat sub- otance, The UM.> of ibe hairs in the human miliject, is not M apparent nfl it is in the inferior animals, in which they obviously protect the body trom external cold. Thej afford u defence lo the skin, and on the head they sem OH iiu ornament. It hns also been Hupposcd that, as they puH from the dermis to the ourface of the body, parfOfi rntin^j;, or nttlivr elon«a(in(,' the rete raucosum and the epidermiii, they must serve to connect lopether all the layers of the intcguiuent« like so many line plus ur fas* Icninga, Of THE NAILS. The naibi, ungticg, like the hairs, are appendages of the itkin, and not merely of the epidermis, alittouj^h Uiey are ho intimately connected with tlie latter, that many authors have described them us being altogether derived from it. These bodiea are hard traOKparent plates, which the don«d extremities of the third phalanges of tlie flngen' and toes. Tlkcy arc oblong in shape, and prvucnl a coo- THBIR UKRCHIPTtON. S/Hl »idcrablti convexity from side to ^iidc. lliv nsiln of the human speci&s differ from those of most aoimnls, by tbeii- com|)arative width nnd by their tenuity. Thciie peculiarities of form and texture relate to the connexion which these bodies huve to the exercise uf touch. ./i£ach nail possesses three parts, vix. the posterior part or root ; the middle part or body ; and the anterior part or free extremity. The mot is the softest and thinnest portion ; it is concealed under the skin, and forms about ooe-sixth or one-fifth of tlic whole nail. The body or principal part of the nail has two surfaces ; the external one is tree, and presents se^'eral longitudinal grooves, which are more or less distinct ; the opposite face inti- mately adheres to the skin. The greater portion of the body has a reddish colour, which, however, does nr)t 1>eIong to the nail, but to the vascular cutis placed be- neath it, and which is seen through ibi lraniv]]arent co- venng. Near the root the nail is opnke and white ; the 0])Acitv, whieli has the form of a half-moon, {la lunule) varies in dificrent indiWduals, but it is always propor-* tioned to the size of the nail. The anterior extremibr; which is the thickest part, passes rather Iwyond the level of the skin, and is conscciuently unattached on both sur* faces. This end requires to be cut from time to time, in proportion as it grows beyond the finger. If this is not done, the nail increases in length and thickness, and ctirves towards the palm of the hnnd, so as to cover the finger, and thus to interfere with touch. In some coun- tries it is a custom among the higher classes of people^' to allow the unrestrained growth of their nails, in order to shew, in an indisputable manner, that they are re- moved from the necessity of manual labour. I1ie connexions of the nail arc rather complicated. 222 coMpnsITlo^f. which nia^ explaia the contnidictions tlmt are met with iu writers on this subject, llie nuil Ls intimately united by its root tttid internal face with the dermis. The for- mer, which in thin and soft, ).s receiiTd into a fold of tlie cutis ; and the l»dy, which is internally soft, and furnished with longitudinal groovM, rGcmi» titv 'ascu- lar ridges of the true skin. The epidermis, which is so firmly attached to the naits, tliat both are separated from the cutis by the some causes, as It approaches the mar- gin of tiie nail, turns towards the root, and thus forms ■ kind of grooved rim, which, being toxcnsible, may be cut away without causing any pain. When the epidermis has reached the root, it is reflected over the external fitce, 80 as to cover it with a very thin and superticia] layer. At the free extremity of the uail, the cuticle of the end of the finger is rvtlected on its deep face, and is then continued, on the external surface, with the above- mentioned layw. The nails are semitransparent, elastic, and resisting ; they tear across, notwithstauding their tibrous appear- ance, in the opposite dire<;Lion. They consist of u homy substance, which has a consi(lt?r»)>]e resemblance to the epidermis. No vessels can be demonstrated, although the constant growth which the nails exhibit, and alao tlicir regeneration after they have been destroyed, prove tliat they receive a supply of blood. Tl»c force of fomw- tion is HO very considerable, that, according to BlumenJ bach, the)' are perfectly renewed about every six monl They do not possess