ORGAN OF TEE SENSE OF TOrril.
This sense may be considered, in the most enlarged acceptation of the term, as residing in the surface of the body in ge neral : m a more limited view, we regard the ends of the fingers as more particu larly adapted, by their organization, for exploring, the tangible properties of bo dies.
The skin, or exterior covering of thebo dy, is divided into three layers, viz. the cuticle, thc rete mucosum, and the cutis. These parts are called the common inte guments of the body. To them a iburth is sometimes added, viz. the adipons membrane. But although there is gene rally a layer of fat under the skin, this is not invariably the case.
The cutis vera, or true skin, is a very dense and compact membrane, formed, ss it were, by a general condensation of the cellular substance on the surface of the body. It is this that forms leather, when subjected to the operation of tan ning. Its thickness varies in different parts of the body. It possesses consider able elasticity-, by virtue of which it yields to any distending power, and on the CCSSa tion of such force recovers its former state. It lia§ also a species of contracti lity, which is evinced by its corrugation from cold. Its colour in the inhabitants of all countries is white. It possesses great vascularity, and has also an abundant supply of nerves, which bestow on it a.cute sensibility. It is thrown into folds in different parts of the body, in consequence of their motions on each other ; this may be particularly observed in the hands and fingers. Its surface is also marked by lines, crossing and inter secting each other variously, and inter cepting spaces of all shapes and descrip tions.
Such parts of the cutis as are the most highly organised have numerous fine hair-like processes, called villi. These are more vascular than other parts. and receive also a more cop;ous supply of nerves. Such parts enjoy a higher and more acute sensibility. This is the case with the ends of the fingers, which, both by- their form and organization, are more especially fitted to act as organs of touch. It is also observed in the lips, and in the glans penis.
The rete mucosum is a soft mucous substance, reaclily demonstrable in the negro, where it is thick and of a black co lour, but hardly discernible in the Euro pean. This is the seat of the colouring matter of the skin.
The cuticle is a thin semi-transparent covering, possessing no particular arrange ment of parts, no vessels nor nerves. It ndhe res, h owever, closely to the subjacent parts, and is exactly moulded to the sur face of the cutis. It is best seen after
the action of a blister, when it is elevated by an effusion of fluid under it. In the dead body it may be separated front the cutis by putrefaction, or by immersion in hot water. In this way it may be remov ed, entire, from the hand and fingers, so as to resemble a glove.
It forms an insensible medium, interpo sed between the nerves of the organ of touch and external objects ; and as it co vers the whole exterior of the body, our surface is actually dead. When removed from any part, it is speedily renewed by the cutis. Its thickness varies in different parts; being greatest where it is exposed to friction, as in the palms and soles. Its thickness is here also inereased by fric tion, as we may observe, by contrasting the hand of a labourer with that of a per son who does not use his hands in the same rough manner.
It appears that the cuticle is impervious to fluids, as the serum contained in a blis tered part does not transude; neither does a dead body become dried while covered by this expansion ; but when that is re moved, it is speedily reduced hy evapora tion to a state of dryness. Yet it must be penetrated by the VCSSCIS in a ing body, as is proved by the immense discharge both of sensible and insensible perspira tion. Probably, also, the absorbents open on it by patulous orifices ; for mercurial ointment, rubbed on the skin, affects the system.
Sebaceous zlands are formed under the skin, in a few situations only, as about the nose and external ear.
Hain? consist of an insensible excre scence produced from the cutis. Each hair grows from a small bulb, and is lengthened by means of additions made to it in the bulb. These bodies perforate the cuticle.
Nails are portions of a horny substance, connected to the ends of the toes and fin gers. Their surface, corresponding to the back of the finger, is convex, and tolera bly smooth; the opposite part is laminated and concave. These laminae adhere to corresponding ones of the cutis. The in teguments advance for some length over the root of the nail, so as to cover a con siderable portion of it ; and the cuticle adheres closely to its surface. The nail grows like the hair, by additions from below.
The account of the progress of the em bryo after conception, or the description of the gravid uterus and its contents, toge ther with the enumeration ofthose etre= •