INTEGUMENTS. 



■fcure ; T cen doubt whether it can be faid to pofTefs life. I 

 am inclined to regard it as afemi-organized, or rather inorganic 

 body, placed by nature at ihe point of communication be- 

 tween external dead matter and the living flcin, and fernng 

 as a gradation between them.'" 



The action of external bodies wears it away, and it is con- 

 ftantly reproduced. Scrape the furface with the blade of a 

 knife, and an abundant greyiih dull will be detached. This 

 matti-r accumulates in greater quantity, when the Dcin is not 

 frequently walhed ; under fuch circumilances there is often 

 a confidcrable layer. 



It is reproduced very completely after being removed ; and 

 differs in that circumilance from moil other tiflues. How 

 this is effeiiled has been a point greatly difputed by phyfiolo- 

 gills ; but the explanations have been entirely mechanical 

 and unfatisfadlory. That it is depofited by the velFels of the 

 fkin cannot be douljted ; and we (hail probably uhderftand 

 how the procefs is eftedled, when we underftand how the 

 veffcls make bone, mufcle, nerve, &c. This reproduftion 

 only takes place on the fldn : the thin pellicle covering the 

 cicatrices of other tiffues has a completely different texture. 

 The different excrefcences affeifting the cuticle, as corns, &c. 

 refult from the exercife of this reproduftive power. They 

 are all infenfible, have no veffels nor nerves, and poffefs the 

 fame confiilence and colour as the epidermis. External pref- 

 fure feems to promote their formation very powerfully ; tight 

 Ihoes produce corns ; and much handling of heavy inftru- 

 ments in hard work produces the thick cuticular covering of 

 the hand » blackfniiths and other mechanics. 



The cuticle of the palms and foles is however originally 

 thicker than that of other parts ; this may be feen in the 

 foetus. 



In the dead body the cuticle has a remarkable effeiS in pre- 

 venting the evaporation of the fluids ; none of which are 

 diflipated fo long as this covering remains entire. If the 

 body be expofed in a high temperature, as of loo or 120', 

 it does not feem to become dried ; and where the limbs are 

 diftended in anafarca, if it has not cracked, none of the 

 fluid cfcapes. Remove the cuticle, and the cutis quickly 

 becomes dry, tranfparent, and horny, and the fubjacent parts 

 are fnbfequently affefted in the fame way. 



Trie epidermis is feen very clearly in the fcetus, where its 

 ■developement is greater in proportion than that of other 

 fyileuis. It may be recognized when the flcin leaves that 

 pulpy ftate which we have fpoken of. At the end of the 

 fifth month it is thicker in the palms and foles than ia other 

 P^'ts. It appears to undergo no change at birth ; but grows 

 rather thicker afterwards as age advances. In the old 

 fubject it differs from that of the adult only in being 

 fubje£i'' to fcale and crack, and thereby appearing dry and 

 plough. 



Internal Epidinnh. — Moft authors have admitted an epi- 

 dermis on the mucous furfaces ; and tliey have generally re- 

 prefentcd that this is the only part of the integuments that 

 liaes the mucous cavities. But a h;tle exami::ation will fliew 

 us that this expanfion forms only a fuperficial flratum, and 

 that if it be detached by hot water from the tongue, palate, 

 &c. an organ analogous to the corion is left behind. 



I . EpidiTmis at the Origin of the mucous Surfaces. — It is very 

 dillinS at all the origins of the mucous fyftem, at the glans, 

 urethra, anus, nafal cavities, mouth, &c. It may be demon- 

 ftratcd in thcfe fituations by the excoriations which fometimes 

 affeci them, by detaching it with a line lancet, by the action 

 of hot water, by maceration, &c. It is much more delicate 

 in thefe fituations than where it covers fl^'in, and becomes 

 iiiore and more fo as it penetrates deeper. In thefe parts it 



is eafily reproduced. It is deftltute, like the exterior epi- 

 dermis, of vital properties ; and its nature feems to be in all 

 refpefts the fame ; it yields the fame refults, when expofed 

 to the fame agents. 



z. Epidermis of the more deeply feated mucous Surfaces. — As 

 we advance further into thefe organs, the epidermis becomes 

 gradually thinner, and foon is no longer perceptible. The 

 moft delicate inflruments and methods do not enable us to de-i 

 monftrate it in the flomach, inteftines, urinary and gall- 

 bladders, veficulEE feminales, and the various excretory 

 paffages. No epidermis is elevated on the furface of thefe 

 organs by boiling or maceration ; nor by bliiters : nor is 

 there any thing hke a feparation of fuch a covering in any 

 difeafes. We fhall be difpofed to conclude, from thefe confi- 

 derations, that there is no cuticle on the deeply feated mu. 

 cous furfaces, and that the laige quantity of mucous 

 fluids poured out in tiiefe fituations fupplies its place by pro- 

 tefting tlie corion from the imprcfilons of noxious matters. 

 The only circumftance that could induce us to hefitate, is 

 tlie occafional feparation of fubllances like membranes,which 

 might be regarded as exfoliations of an epidermis. Nume- 

 rous examples occur in medical writers of fuch matters being 

 voided from the bladder, flomach, and inteftines. On this 

 fubieft we poffefs no very precife data. 



ihe Nails. — We connect the hiftory of thefe organs with 

 that of the epidermis, as they adhere to it very Ifrongly, 

 a'.;d come- away with it in maceration. Their form in the 

 human fubjett differs very much from that wliich they have 

 in animals ; they are generally thick and conical in the latter, 

 thin and flattened in the former. They confift of hard, 

 tranfparent, and elalUc plates, of a fubilance refembling 

 that of the horns of animals, covering the extremities of the 

 fingers and toes on the afpeft of extenlion. Thus they are 

 not adapted to purpofes of offence, but are better fuited to 

 the fupport of the broad ends of thele members, which confer 

 on the human fubjeft a more perfeft power of touch. Their 

 length is limited by the univerfal practice of cutting them 

 to a level with the end of the finger or toe : if left to them- 

 felves, they are prolonged, and at the fame time bent fo as to 

 cover the ends of thof'e parts. The natural limit of their 

 growth feems to be that period at which they acquire a fharp 

 cutting edge : for they are then gradually worn away at thp 

 margin. 



Three parts may be very eafily diftinguifhed in the nail : a 

 polterior portion, covered on botli fides by integuments : a 

 middle part, which is the mofl coniiderable, adhering by 

 its concave, and unattached on its convex furface ; and an 

 anterior, free from adhefion in both refpe<fts. 



The poilerior diviiion is about one-fixth of the whole : 

 it ends behind in a very thin ferrated edge, by which the 

 nail feems to grow out of the fl<in. This part is foft and 

 flexible, and of a white colour : it is bounded by a flraight 

 line, which, with the two margins, give to the organ a 

 fquare figure. The convex furface adheres intimately to 

 the epidermis, which cover* it in the following manner. 

 The cutis terminates over the root of the nail in a femi- 

 lunar edge, in front of which is a fmall cavity adapted to, - 

 and filled by, the white part of the nail. Along the con- 

 cavity of this crefccnt the cuticle forms a fmall and diftinft 

 fold, wliich may be cut without any feeling of pain, and 

 which is reproduced. It adiieres clofely to the root of the 

 nail, and is produced anteriorly for fome length on its fur» 

 face, unlefs it be cut away. Many defcribe it as being con- 

 tinued over the whole convex furface. Beliind it appears 

 to be lofV in the foft and thin poflerior margin. Without 

 the adhefion, which connefts the lemilunar border of fltin 



