CHAPTER X.

TOUCH.

General Observations on Touch-Its Universal Diffusion over the surface of the Body-External Integuments-The Scarf-skin, forming the barrier between the living and the dead-The Mucous Web, the especial seat of Colour-Albinos -Remarkable case of a dark Hindoo becoming fair-True Skin, that of which Leather is made-Its External Surface the immediate seat of the Sense of Touch-Tact and Touch-All parts not equally susceptible to the impressions of Touch-Informs us of the condition and properties of External ObjectsThe most important Guardian of the Body-Less liable to be imposed upon, and to bear false witness, than the other Senses-The confidence placed in it-The superiority enjoyed by Man in the excellency of this Sense-Case of J. Mitchell, born Blind and Deaf.

By sight and hearing we become cognizant of the existence of distant objects, and we have seen how admirably the instruments are constructed for affording us the information they are destined to communicate, and how accurately they accommodate themselves to the varying conditions of the causes which excite these respective sensations. By means of touch we are informed, in the first place, of the form and size of objects, and of the resistance they offer, thereby giving ideas of smoothness, roughness, hardness, softness, and weight. In the majority of these instances, if not in all of them, the sensation communicated results from the combined impression made on the surface of the organ brought in contact with the object, and the degree of muscular effort necessary to oppose or overcome the resistance presented. Secondly, by the same sense we are able to judge of the differences between the temperature of external objects and that of

our bodies, which excite in us the feelings of heat and cold. Self-preservation depending more immediately on this than any other sense, the faculty is not limited to any particular situation, as is the case with the other senses, but it is diffused generally over every part exposed to external influences. The skin, however, is especially endowed with the susceptibility to impressions which originate the sensations of touch, and in this respect it varies in different situations, some parts, from a favourable combination of structure, being better adapted for receiving and transmitting accurate and definite sensations

than others.

We have already had occasion to take under our consideration the external integuments, in so far as they exercise the functions of secretion and absorption, and have now to examine them in reference to the function of touch. The external integuments consist of three layers, which require special notice, namely, the cuticle, mucous web, and true skin.

The Cuticle, or Scarf-skin, forms the external investment of the body, and varies in its texture and thickness in different parts. It does not present any particular organization, nor have blood-vessels or nerves been traced in its structure, but it appears to be the product of the subjacent vessels. These vessels pour out an albuminous secretion, which, by the influence of the air, becomes converted into the cuticle-a change similar to that which takes place in the coagulation of the white of an egg. The cuticle then may be considered as an indurated pellicle, serving as a barrier between the living parts of the body and all that is external to it. It varies very much in thickness and consistence in different parts, according to the condition of the subjacent vessels from which it is derived, and forms an exact mould of the surface which it covers. From its being translucent, the colour of the parts beneath shine through it, though from its not being perfectly transparent, the tints are somewhat

modified by their transmission. When the surface of the body is exposed to irritation, the vessels that pour out the lymph, from which the cuticle is derived, have their action increased, and the cuticle either becomes thickened, as in the palms of the hands and soles of the feet, or the effusion is so abundant as to cause a separation between it and the true skin, producing blisters. The thickening of the cuticle from pressure affords one of the innumerable examples of design which the construction of the animal body so admirably displays. Had this tissue been subject to the general law, in virtue of which pressure excites absorption, as exemplified in the internal organs under various diseased and other conditions, it should have been rendered thinner, and consequently less capable of affording due protection under the very circumstances where protection is most necessary; but instead of this, pressure causes the cuticle to become thicker and more dense, that it may serve as a shield to the parts it covers. It is perforated by millions of minute pores, which allow of the escape of the matter of transpiration, and of the sebaceous secretion. It is constantly being renewed from the internal surface, and as constantly peeling off from the external surface, in a fine powder, or in thin scales. After some diseases, as scarlet fever, and other affections in which the integuments are much involved, it is often completely renewed, the old scarf-skin being thrown off in large patches.

The cuticle is present in all organized beings, plants as well as animals, though it presents, as may be readily supposed, great diversities in appearance and structure, according to the rank of the object for which it serves as a protection. In many reptiles and crustaceous animals it is cast off at certain periods in one mass, when it presents an exact mould of their bodies, their scales and other external parts being exactly represented.

The Mucous Web.-Immediately under the scarf-skin is situated a soft pulpy network, exceedingly thin in

the fair European, but much more apparent in the darkcoloured races, especially in the Negro. It appears to consist chiefly of the shaggy extremities of blood-vessels, interlaced and bound together by delicate filaments of cellular membrane. This is the immediate seat of colour, the colouring matter, consisting of minute globules, varying in their tints in the different races;—even the different nations of Europe are characterized by the colour of their skin. It has been supposed that the colour of the skin depends upon the intensity of heat and light to which the body is exposed. It is true, that in tropical countries, the colours of both plants and animals are more intense and brilliant than in colder regions, and that exclusion from light produces a pale blanched appearance, while exposure to it has a contrary tendency; but the variations thus produced in the colour of the skin are neither permanent nor do they descend to the offspring. In every variety of the human race, as well as in the lower animals, examples occasionally happen where the mucous web is totally devoid of colour, such individuals being termed Albinos. Their skin has a somewhat disagreeable deadly white appearance; their eyes are bloodred, from the absence of colour in the iris and choroid membranes, and their hair is also colourless. These accidental occurrences are not easily accounted for, though apparently they have a tendency to run in families; and it is possible, that by attention to breeding in and in, a permanent variety might be established. At Lasswade, a village five miles from Edinburgh, there is a family of seven children, two of which are albinos, a male and a female. The parents, and particularly the father, were what would be termed swarthy; the other brothers and sisters are also dark-complexioned. In every respect they enjoy ordinary health and strength, but are less able to tolerate strong light, though they do not see better than others in obscure light. A few years ago, there was a very remarkable instance in Edinburgh of a

Hindoo, advanced in life, who came over to this country when a boy. At an early period of manhood, white spots began to appear on different parts of the skin, which, in progress of time, gradually enlarged, so as ultimately to spread over by far the greater part of his body, leaving on the face a few black spots, as also a few patches on the trunk and limbs. In this case, the colouring matter of the mucous web was not entirely removed, but merely replaced by globules of a whiter colour. I attended this individual during his last illness, and afterwards examined the body, whereby an opportunity was afforded for obtaining a portion of his spotted skin, which was carefully examined, without being able to ascertain the cause of this curious change. He was well known in Edinburgh, and must still be in the recollection of many, as his case excited some curiosity among medical men, as well as others. The white portion of his skin was as fair as that of the majority of Scotchmen, and the spots as dark as the skin of the darkest of the Hindoo races. married to a Scotchwoman, and had a family as fair as their mother, but with the Hindoo features so well marked as not to be mistaken.

He was

The Dermis or True Skin.This is the thickest and most important part of the external integuments. It is composed of an infinite number of plates, consisting of filaments inextricably interwoven together, and abundantly furnished with blood-vessels and nerves. Externally, its texture is most dense, becoming softer and looser, and gradually passing into the common cellular tissue beneath. Its thickness varies in different parts of the body, as also according to the age and sex of the individual. On the back it is nearly twice the thickness that it is on the anterior surface of the body, and much thicker on the outside of the limbs than on their inner surfaces. It is chiefly composed of animal gelatin, and by being combined with the vegetable principle named tannin, becomes converted into leather. It is everywhere