Section IV, (Part 2)

any ner^'es, and, consequently, tht are totally insensible. These bodies begin to appear towards the middle of the foetal existence ; but they are impcrfi-ctly for even at the time of birth. They are chicAy composed FUNCTIONS OP TUB 9KtN. 2'23 albumen, with different propwdons of jelly and mucus ; the)- also appvar to contiiin u Hide of the phosphate of lime. The ufles of the nails are contined in the humnu species to increasing; the perfection of the organ of touch. They support the skin on the oxtremili^i of the fingers, and preser^'C it in the stale of tension which tits it to receive the stijihtest irapressioni). When the DaiU are lost, the »kin shrinks, and Is, in a great degree, deprived of its delicate sensihility. SacmoN VI. FUNCTIONS or THE SKIV. In many of the inferior animaU the tliick and even homy integument serves as « kind of umour against mechanical violence. But in the human species the de- fensive power of the skin, is principally limited to pro- tecting the surfiice of the body from tJie injurious influ- ence of chemical agents. This important object is ac- complished by the secretion of the small arteries, and of the sebaooous follicles. The capillary vessels of the skin .secrete a water>- fluid, which ifi constantly pa&sing off from the external sur- face, either in the form of vapour, when it is called the insensible perspiration, or in that of Uquid, when it is dis- tinguished as the sweat. Many circuDisbances affect the cutaneous transpiration, especially the condition of the atmosphere and the state of the individual ; it is, there- fore, difficult to fr>rm an accurate estimate of its iiuan? 2S4 CCTANROUS TRAKSI'IRATIOK. lity.* The expetim^U which were peifotUMd»itfa.4w much core aod Hkill by Lav-oilier and Seguio, to deUnnw this point, are geoeraUy coosidered to be aaiu&cUvy. According to their authorit)', the avera^ diachMgia 6nm tbc akiD amounts to thirty ounces, and thM froofitbe loOgS to fifUcD OUDCC& iu tWi-UtV-fuUT hoUTH. It U Kg*} thy of rvnuirk that Hailer had previouijy oitiioated i% imwDKibli.' |>erKpiration at twenty-eight uunce-s in t«(R|^ four hoiini, aacl that, t>tit>sequenlly, Mr. Ahentttt^/^^ found that about two pounds and a hall' of a«|U4m^pU art punipired daily from a person of ordiitaf^ tilnlQ^tlC ■The triuupired fluid is uHuidly iinpiTceptibU. in om> )ui;nce uf hein}{ carried otf by cvnpuriition m tjuickjy a» it is tieparat^d tironi the blood ; but when from i« increased acting of the capillary arteries, or frDm a di- minution of the solvent powers of the atmosphere, if from botli tliCKc caul's united, the secreted inutt«»- is uot iromedintvly evaporated, it uccumulaUK in small (lro|N on the suriace of the skin, and thus fomib the lieatf^ penpinttion, or sweat. - ^ The matter which is excreted appears to ^r fifnim|ill||l the same in uich instance, the only dilferi:oce TfiUtj^^lC ibt quantity. It cunKist^i of water, which Ituldaii tion hydrochlorate of potash and soHa, lactic or acel acid, and a i^mall propiirtion of animal matter, proh^l mucus or albumen. The ciiUineous transpiruliotj, ii may jud^ by its odour, has not always the htane tf tics. It has n strong smctl in the armpibi and fivt of many persons, and it is especially nauseous and di»agia;)t, * The rxodlntt woft or Dr. rdnwd* oontiku m grart deal of <«laibl« Hit (oRMlion on lhi> uilgeot. Stc •■ De I'lnfluraoe in Agcoi PhjrHqMn W jl^ Vie," pi 312, ft w^. USR OF IT. 22B able in Negroes. The cutaneous transpiration ought to be regarded as a necessary and important cxerctJon, for whenever it is diminished or suspended, serious disturb- ance is produced in the economy. The perspiration has also a great influence in reducing the beat of the body. This is proved by the observations of Dr. De la Roche and others, who found that aaimals are capable of resisting u high temperature in proportion to the cutaneous evaporatioQ. The researches of Cruikshank, and the later ones of Mr. Abemethy, prove that the air in which the hand or foot was confined for a certain time, contained a quan- tity of carbonic acid ; and Dr. Edwards has shewn, that in frogs and other inferior animals, the respiratory pro- cem of the skin is nearly equal to that of the lungs. It is therefore probable that the skin secretes carbonic add, but that the quantity is small in man, in whom the pulmonary organs are so greatly developed. '«>■ The surface of the body is bedewed with un oily mat- ter, which is secreted by the sebaceous follicles. Cruik- (ihank obtained this substance from the surface of a flnnnel waistcoat which he had worn during a month in the hottest time of summer. It consisted of a black and " Th« «sp«rim«nti of Sic C. Bla^den, D(. SoUndiT, aotl olben, allowing Ibe powR wh4cl> the inimal body pfmatct of Kiiiling (or a time » high torn- pmiut*, are wtW known. I have lately had ad oppottunity of witnewlag it MmtiM experiment, »hicli waa performed by Moni. Ch&bi-rt. This person went into >D uvrti, of which Ihe t^nipL'tsltite wiui S'j(f ; he leniaincd (here about •even nimulct, nhicU time wai sufficient Vi couk the tKvf-slc-.iks lljut he look •ilh htm into ihr ovrn. He came out in a profuse ponpiiation, and hit pul»e, wliurh t uccituntMl were 96 at the beginning oS the experiment, had riwa to 160. Wilh the exception of these ellecli, lie did Dot appear, either whiltl in 8m OTtn or aAerwvdt, 10 be in tbe least inconvcnieDccd by thii cutioui pct- fomaare. 1 have bMtd from others, that M. Chabcrt haa freiumily goae iiilo dw ovea at a much higher lempccaiure than that above mentiooed. J tS6 ABSOBBIIK of) iflTpenpinboB. & ■eocCKM of the Tbc ahMffting power of the fricDoB,. or by the cfansioa ctf tkc gnenfly dn^tcd by iDodvii p^BoiofiitB. A coMtni; ■nywHt WB enlertmtned bf SiBCloriiB, aDd by tnktn wbo wptted hia eiptriintafc. The uiwat^lioM of Dr. Erfmnb,* «rfpdi have done bo modi to detemiBc mftOT of the disputed tfaasdoas of phniology, shew that abMnptioD taket place, to a very coosidenlile exteot, without frictioa or ahraaion. This ««5 proved by placfatg frogs, toads, and fizards in water, when it ww found that thdr weight wait increased by cutaneous ab- •orptioo. Bui ID nuLktng this statement, it is oot in- tended to di>ny Uiat friction, and still oiort the rcmoni of the cuticle, greatly increase the absorbing power «^ the turiace of the body. ^^| The ob»ervationii of Mr. Abemethy would lead as 10 conclude, that the sitm aIm) absorbs certain gaseous sub- stancefl, in aiiditinn to aqueous roattur. Thus he found that the hand mid wrist imbibed eight ounces of oxygen gM in eight houn, and one ounce of azote in the same period. The last function of the skin which remains to be ronitidcrcd, is that which depends on the sensibility with which it id endowed. This property is greatly developed * 0,1 rtnSimn-, ke. |>. 34S. rt Mf. TACT AND TOUCH:- io the human species, coafctring a delicacy of sensation which is wanting in aniniHls. Ever)' portion of the ex- ternal surface i-s capable of recciring the imprcHsion-t of surrounding bodies ; but many of their ciiialities can only be asctrtained in an accurate manner, by a small part of the skin. These two modifications of cutaneous sensi- bility have been dislinguislicd by the names of tact and touch. Tact is exercised generally over the skin ; whilst the aense of touch is confiued to the hands, and in a lesH degree to the feet. The latter being more perfect than the other senseii, and less liable to error, has been called the geometrical sense, A very little reflection, however, will convince us, that most ph)siologists have consider- ably overrated llie perfection of this function. Q'2 i S3S Mrcocft PART THIRD. OP Tn MUCOUS tBM iiiintHis nienibmics fbnn the '"'— i"l portiuB of the tegameatarj sntan. The name wis qifdM in ifce fint instance, to the membrane erf the nostifls, in ■equence of the mncns which it seoetES. In the in, the term has been extended to the rrwin| filing of all those avitks which hare extanal rtwimi- nicatioDi ; so that, conadered in this manner, it is much more extensive than the sidn. The amilaritT of dw secretioD of the different parts of this sntan, and the general existence of follicles throughout its Tarions <Ern- aons, caused anatomists to suspect that all diese mem- branes were identical in their structure, and subsequoit investigations have satis&ctorily confirmed these sar^ mises. The honour of giving the first distinct histoty of these textures, is due to Bichat ;* although Pinel had previously remarked their similari^ in a padiological point of view. Skction I. DlSPOfllTION OF THE MDC0U8 HIHBBANIB. Tbi cavities and organs which are lined by these membranes, are placed in such distinct regions of the ■ SMTnUdeilhmbraiin. CONMBXIONU J "J * 239 body, and they are otherwiae so distmct from each other ID structure and function, that it is difficult to conceive that tfa«y an: all connected together by u continuous sur- face. Anatomical examination, howcTi-er, proves this continuity in an incontrovertible manner ; and in order to render it appareat, I shall follow the example of Bichat, who demonstrated that all the membranes of this system might be reduced to two great divisions, viz. the gastro-pulmonary and the genito-urinary. i.The first division enters the interior of the body through the mouth, the nostrils, and the laclirymal passages. After lining the oral and nasal cavities, it is rejected from the former along the excretory tubes of the parotid, submaxillary, and subltnguul glands-; wliil&t from the latter it is continued within the dif- ferent sinuses of the head. Iliat portion which belongs to the lachrymal passages, afler having covered the surface of the eye and eyelids, is reflected at the external part of the globe, along the ducts of the lachrjinal gland ; and at the internal canthu-t it extends within the lachrymal puncta, the lachrymal sack, and the nasal duct, and in tiiis manner becomes continuous with the membrane of the nostrils. The mucous surface of the mouth and nose is then continued buckwarda into the pharynx, from each side of which it passes along the eustadiian tube, and thus reaches the cavity of the tympanum and the mastoid cells. At the lower part of the pharyngeal bag, the membrane sends off two pvat processes; the anterior one being reflected through the larynx, the trachea, and the bronchi, penetratea into their minute terminations, which constitute the air-cells ; the posterior portion extends along the aso- phagus, lines the stomach, and then enters the duo- 330 CONNEXIONS. denum. In this intestine tlie mucous membrane fiir- nisbea two processes ; one of which is prolonged into the ductutt choledochus, into the ductus bcpaticus na far as its origio, an<l into the ductus cysticus and gall bladder ; the second portion lines the ductus pan- creaticus and iu numerous branches. The mucous sur&ce is continued from the duodenum along the re- maining part of the smidi intestine ; it then enters the large intestine, and ultimately ending at the kdur, it Bgain becomes continuous with the external integument. The second great division of the mucous system, the genito-uritinry, is much less extensive than the first, although it penetrates verj- deeply into the interior of the body . In man it enters by the orifice of the uretlira ; it lines that canal, and at its prostatic portion it sends off some processes, which pass into the ducts of the prostate gland ; and others which are reflected on th« one part, along the excretory tubes of the vesioilie Mminales, so as to afibrd a lining to those bodies, and on the other, alonsr the rasa deferentia and their com- plicated ramifications within tho testes. The mucous membrane is afterwards continued from the urethra into the urinary bladder ; it lines that viscus, the ureters, the pelves of the kidneys, the infundibula, the papiUse, and in all proludnlily the uriniferou.4 tubes. The membrane in the female enters the vulva; one portion of it is reflected through the urethra, and then within the urinary passape.s, as in the male. The other port lines the vagina, the uterus, and the futlopiao tubes, and becomes ultimately continuous at their fim- briated extremities with the serous membrane of the broad ligaments. In the preceding enumeration I ha%-e not iflchKkd ADUBRBNT AND FRBE SURFACES. 98l> a small insulated process of itie incnibmne, wlilch lines the lactiferous ducts of tJie female mamiDGC ; it is, in conswjucncc of its small extent, comparatively unim- portant. The adherent surface of the mucous memlnranes is united by cellular tissue to the various parts by which thej- are surrounded. The principal division of this system is joined U) the plane of fleshy fibres that be- longs to the alimentary canal, and which constitutes a kind of internal cutaneous muscle, in other places, as in the larynx and air-tubes, the membrane is con- nected witli a cartilaginous structure ; and elsewhere, to a lig;amentou8 texture, as to the periosteum of the nares, of the sinuses, palate, Sic. The firmness of the above connexions is variable ; it is inconsiderable in the nasal fosss, the intei^tinal canal, and the urinar)* bladder ; whilst the uni(3n is very in- timate ou the ttm^e, the palate, &c. The tree surface possesses a ver>' complicated struc- ture, which is subsen-ient to the important functions that are exercised in the mucous membranes. It has an unequal appearance, in consequence of numerous valves, folds, and wrinkles, projecting on most parts of its extent. The valves are formed not only of du- plicaturcs of the mucous membrane, but also of the subjacent muscular fibres ; there are examples of them in the vtive of the pylorus, in that of the ileum, and in the vdum palati. The folds contain only the sub- mucous tissue witliin them ; they are, however, as eoo- stant as the valves, and are never obliterated by dis- tention ; such are ttie valvulse conniventes of the intes- tines, and the spiral projections within the cystic duct. The wrinkles, on the contrary, depend on occidenlal SccnoT EL OftGA3iIZAT103I OF THI HrCOCs TkB bans of tjhoe manfacKH exmaatb^of m kw of eomfauad rrn^a^ sdH&Bce. wtadi -was deaoaiaaled br' Bidut, from iB naesBMuiee to tbe coriactOM part ^ the skin, the mucuiB er.xium ; it has also beoi vsuHr' distinfoisbed in the sfaiiKDtuT cunl. bv the i™*— of tonica nerreft. Tliis lunina sopptHts t Tvscnhr and de- licate Ktnicture, whiefa fonos the eztBuI stahet of the nuBDQS sTston. It has be« shewn, in a fanner part of this AafUr,- that the e|Hdennis can be demonsbated in sercral parti of this system, and that in 'certain tfirections, as aloiif the osophagos, it penetrates rather deeply into the body. Bat in moat of the intenuJ organs, it qipeare that the l^ace of the epidermis is supplied by the mucous seen-- tioD, which affords an effidmt protection against the foreign substances that are constantly passii^ throogfc MUCOUS coatuM. 9M' l^gfio.: Haller, and others, entertained an opposite opinion, and urged in support of it, the oocasionoJ dis- churgv from ttu: stomach, bladder, &c,, of membr8n(.<a baNong tlii> i-xact form of t)io&c organs, and which were thought to he thur cuticular lining. It is certain, how- ever, : that these membranes must have been portions of fibrin, which were produced by inflammation. There is no structure that can be assimilated with the corpus mucosum of the external integument, and con- sequently ID the Negro the mucous surlaces have the same appearance as in Uie European. One exception, perhaps, ought to be made, viz. in the tongue, where the papillee are separated from the epidermis by a Uyer of coagulable liquid, which, in fact, being observed by Malpighi, led to the discovery of the subtttance which has since been distinguished by the name of that cele- brated anatomist. I,, The mucous corium forms the basis and suppcurt of tiffi mucous system. It« thickness varies in the different nipous which it occupies. It is extremely thin in the, sinuses of the head, and in the excretory ducts ; it be-i offines successively thicker in the urinary bladder, in tbfii large intestines, the gall-bladder, the small intestines, the stomach, the nasal fossn:, the palate, and the giuns.: The density of this membrane also exhibits variations,, whicii are very apparent by comparing a part that is placed towards any of the external openings, with another portion taken from the interior of the body. The cel- lular tissue which forms the corium of the mucous mem- brane has not, like the tissue of the cutaneous dermis, a regularly areolated disposition ; it is generally fibrous, but in many parts, and particularly in the pituitary mem- brane, it has a spongy or even fungous structure. 3M TAriLLM. AMD TIUJ. ^ic mneoiu ooniua is covanl dv a tare, iriudi is anatogoiu to the payjim} tm the ooter saxfaee of the eutkvam; it pqHibe, vilU, aad fiJlides. or TBI PAPILLA AMD TILU. These bodies, which consist of an infinite projectioiis, have received their appdktioB froai snf^MJsed resemblance to small nifties and to Ike velvet. The papOim are snflScientlj large to be ae^ hy Ae naked eye, particularly on the tongue, when tber «e very much developed. On the dmsom of dns orfsa, there are four classes of papilbe, which are distiBguiahed according to their various forms into die fiUfcna, tte conical, the Amgiform, and the lenticular or truncated. Their size is also subject to variation ; and hence Am are termed the papiihe majons, mediie, &c. The vilK or villosities are much smaller dian the piv- eeding eminences, and indeed the aid of a lens is usi^ly required to see them distinctly. In the small intestines they are larger than (hose of the stomach ; their Iei^;di is usually about the l-4th of a