ANATOMY. 
generally diftinguifhed in the nail; the root, body, and 
extremity. The root is white, and in form of a crefcent; 
and the greateft part of it is hid under the fepiilunar fold 
already mentioned. The crefcent and the fold lie in con¬ 
trary directions to each other. The body of the nail is 
naturally arched, tranfparent, and appears of the colour 
of the cutaneous papillae which lie under it. The extre¬ 
mity of the nail does not adhere to any thing, and dill 
continues to grow as often as it is cut. The principal ufe 
of the nails is to ftrengthen the ends of the fingers and 
toes, and to hinder them ftom being inverted towards the 
convex fide of the hand or foot, when we handle or prefs 
any thing hard. For, in the hand, the ftrongeft and mod 
frequent impreilions are made on the tide of the palm; 
and, in the foot, on the foie; and therefore the nails ferve 
rather for buttreffes than for fliields. 
The hairs belong as much to the integuments as the 
nails. The roots or bulbs lie toward that fide of the fkin 
which is next the membrana adipofa. The trunk or be¬ 
ginning of the Item perforates the fkin, and the reft of the 
Item advances beyond the outer furface of the (kin, to a 
certain diftance, which is very various in different parts 
of the body. When the different hairs are examined by 
a microfcope, we find the roots more or lefs oval, the 
largeft extremity either being turned towards, or fixed in, the 
corpus adipofum. This oval root is covered by a whitifh 
ftrong membrane, in fome meafure elaftic; and it is con¬ 
nected either to the fkin, to the corpus adipofum, or to 
both, by a great number of very fine veffels and nervous 
filaments. Within the root, we obferve a kind of glue, 
fome very fine filaments of which advance toward the 
fmall extremity, where they unite and form the ftem, 
which partes through this fmall extremity to the fkin. 
As the ftem paffcs through the root, the outer membrane 
is elongated in form of a tube, which clofely inverts the 
ftem, and is entirely united to it. The ftem having reach¬ 
ed the furface of the fkin, pierces the bottom of a fmall 
foffula between the papillae, or fometimes a particular pa¬ 
pilla; and there it meets the epidermis, which feems to 
be inverted round it, and to unite with it entirely. A 
fort of unCluous matter tranfudes through the fides of the 
foffula, which is bellowed on the ftem, and accompanies 
it more or lefs, as it runs out from the fkin. 
Hairs are fcattered almoft over the whole furface of the 
body, the palms of the hand and foies of the feet except¬ 
ed. They differ in length, thicknefs, and folidity, in the 
different parts of the body. Thofe on the head, are call¬ 
ed in Englifh by the general name of hairs ; thofe which 
are difpofed archwife above the eyes, fupercilia or the eye¬ 
brows-, thofe on the edges of the palpebrae, cilia or the 
eye-lajhes-, and thofe which furround the mouth, and cover 
the chin, the beard. In other parts of the body, they have 
no particular names; and their different lengths, thick- 
pefles, &c. in all thefe parts, are fufficiently known. Their 
natural figure feems to be rather cylindrical than angular, 
which is chiefly accidental. Their colour is probably the 
lame with that of the glue, or medullary matter of the 
root, the different confidence of which makes the hairs 
more or lefs hard, flexible, &c. Their ftraight or crooked 
direction muft depend on that of the holes through w hich 
the ftems pafs. The hairs^grow continually, and are re¬ 
newed again after being cut, by a protrufion of their me¬ 
dullary fubftance from the fkin outwards under a produc¬ 
tion of the cuticle. When they are deftitute of this me¬ 
dulla in old people, they dry up, fplit, and fall off. They 
feem to perf’pire through their extremities, and poflibly 
through their whole furface; as we may conclude from 
the conftant force of protrufion in their medulla, which in 
the plica polonica wants a boundary to terminate it. 
Befides the integuments which have been already deferi- 
bed, the ancients reckoned the panniculus carnofus, and 
membrana communis mufculorum. The panniculus car¬ 
nofus is found in quadrupeds, but not in men, whofe cu¬ 
taneous mufcles are of a very fmall extent, except that 
which is called platyfma myoides in particular; but even 
Yol, I. No. 37. 
S9 
that mufcle cannot in any tolerable fenfe be reckoned a 
common integument. There is no common membrane of 
the mufcles, which covers the body like an integument; it 
being no more than particular expanfions of the membranes 
of fome mufcles, or aponeurotic expanfions from others. 
The elongations from the lamina of the membrana adipo¬ 
fa or cellularis, may likewife have given rife to this miftake, 
efpecially in fuch places where this membrane is clofely 
united to the proper membrane of the mufcles. 
The fenfe of feeling is to be underftood in a two-fold 
manner. Every change of the nerves, produced by the 
heat, cold, roughnefs, fmoothnefs, weight, moifture, or 
drynefs, of external fubftances applied to any part of the 
body, is commonly called feeling. In this fenfe, feeling is 
aferihed to almoft all parts of the human body; to fome 
more, to others lefs, as in different places of the body 
the nerves are more numerous and bare, or covered with 
more tender membranes; and thus even pain, pleafure, 
hunger, third, anguifh, itching, and the other fenfationsj 
belong to the fenfe of feeling. In a more peculiar fenfe, 
feeling is faid to be the change arifing in the mind from 
external bodies applied to the fkin, more efpecially at the 
ends of the fingers. For, by the fingers, we more accu¬ 
rately diftinguifh the qualities of tangible fubftances than 
by other parts of our body. 
The papillae, regularly difpofed in the fpiral folds at the 
ends of the fingers, on the infide of the hand, may, by the 
attention of the mind, become ereft or elevated ; and, be¬ 
ing in this (late gently preffed or rubbed againft a tangible 
fubftance, they receive an impreflion from that fubftance 
into their nervous fabric, which is thence conveyed, by 
the trunks of the nerves, -to the brain. This is what we 
call the touch, whereby we become fenfible chiefly of the 
roughnefs of objects. Some perfons have this fenfe fo 
acute as to be able to diftinguifh colours by touching the 
furface only. By this fenfe w r e perceive heat in thofe bo¬ 
dies which exceed the heat of our fingers; and weight, 
when the body prertes more than is ufual. Humidity we 
judge.of by the prefence of water; foftnefs, by a yielding 
of the objedt; hardnefs, from a yielding of the finger; 
figure, from the limits, or rough circumfcribed furface; 
diftance, from a rude calculation or eflimate made by ex¬ 
perience, to which the length of the arm ferves as a mea¬ 
fure. The touch ferves to correct the miftakes of our other 
fenfes; but yet it fometimes errs itfelf, and then the other 
fenfes (hew themfelves to be true guides to the animal with¬ 
out touch. 
The corpus mucofum moderates the adlion of the ob¬ 
ject touched, and preferves the foftnefs and found ftate of 
the papillae. The cuticle excludes the air from wither¬ 
ing and deftroying the fkin; qualifies the impreflions of 
bodies, fo that they may be only fufficient to affect the 
touch, without caufing pain. When, therefore, the cuti¬ 
cle is become too thick by ufe, the fenfe of feeling is either 
loft or leffened ; and, if it be too thin and foft, the touch 
becomes painful. The hairs ferve to defend the cuticle 
from abrailon ; to preferve and increafe the heat; to cover 
what ought to be concealed; to render more irritable the 
membranes of thofe parts, which ought to be defended 
againft the injuries of infedfs; and perhaps to exhale fome 
tifelefs vapours or oil. The nails ferve to guard the or¬ 
gans of feeling, that the papillae and ends of the fingers 
may not be bent back by the refiftance of tangible objedls : 
at the fame time they increafe our power of grafping large 
objects, and aflift in handling minute objects. In brute 
animals, they generally ferve as weapons of offence, and 
might be of the fame ufe to man, if they were not cutoff. 
One moft important office of the fkin is, to exhale front 
the body a large quantity of humours, and to reforb va¬ 
pours from the air. The fkin is replete with an infinite 
number of fmall arteries, either coiled up into papillas, or 
parting direflly through it, which afford a paffage to the 
exhaling vapour; and, left this vapour ffiould be coliedled, 
as it is in fome difeafes, between the fkin and the cuticle, 
there are pores in the cuticle correfponding with the exha- 
7 L ling 
