This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
16. In insects, the antenna or feelers, are the organs of touch. These are of a great variety of forms, very flexible; and constantly in motion, when the insect is walking. If the feelers of an insect are cut off, it either remains motionless, or if it attempts to fly, it appears bewildered and lost. It is by means of their feelers that bees are able to work in a hive without light, and build their cells with the greatest regularity ; by them also, they communicate to one another their impressions and their wants.
17. It is supposed that the different modes in which ants touch each other with their feelers, when they happen to meet, constitutes a kind of natural language, understood by the whole tribe. It is evident that they could not co operate in their labours without some kind of language. When an alarm is given in time of danger, one ant strikes his head against the corselet of every ant which it chances to meet, and these repeat the same act to all that fall in their way, and so the news is quickly spread through the whole society.
18. Sentinels are always placed on the outside of ants' nests to apprize the inhabitants of any danger. When an enemy approaches, these guardians quickly enter the nest and spread the news in the way just stated, and soon the whole swarm is in motion. While a larger proportion of the ants rush out to repel the attack, others, who have the office of guarding the eggs and the larva, or eggs, hasten to remove their charge to places of greater.security. These acts all depend on the faculty of touch, so that it is as important to the lower animals as to man.
19. Sight, hearing, and touch, have been called intellectual senses, because they are the means through which we obtain our most valuable information, the witnesses that furnish the evidence of the existence of external things. We can have no doubt as to the evidence they deliver, if they all agree in their report. We find however that if we depend on either alone, we are liable to be deceived. Sight is liable to many illusions ; we may, under the influence of the imagination, or of a diseased brain, imagine that we see a thousand strange sights, ghosts, hobgoblins, spectres, and devils ; or from similar causes, we may believe that we hear strange and unearthly sounds; but if we attempt to touch the objects which appear to present themselves to our vision, or which discourse such unnatural music, we find that they vanish before us, like the ignis fatuus, or jack o'lantern, which we may chase " o'er bog, and o'er moor," but we can never lay our hands upon it. I have often watched, with a degree of wonder, the action of a patient labouring under drunken delirium ; the unhappy maniac not only sees strange objects about his bed, and flitting before his eyes, but he hears them singing and talking to him ; he puts out his hand to grasp them,-he grasps nothing,-still he is not undeceived, nothing can make him believe that what he sees and hears are only the phantoms of a diseased brain ; he persists in endeavouring to seize, to touch the strange objects, and only ceases, when after days and nights of incessant vigilance, his strength exhausted, he either sleeps or dies !
20. Touch has, therefore, been relied on in every age, as the most certain of our senses, and it is well to recollect that the most important fact that ever occurred on the theatre of this earth, viz. the resurrection of the Saviour, .is established by the testimony of the three intellectual senses. In the gospel of the evangelist St. John, we read, "But Thomas, one of the twelve, called Didymus, was not with them when Jesus came. The other disciples therefore said unto him, we have seen the Lord. But he said unto them, except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe. And after eight days again his disciples were within, and Thomas with them ; then came Jesus, the door being shut, and stood in the midst, and said, peace be unto you. Then saith he to Thomas, reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side; and be not faithless but believing. And Thomas answered and said unto him, my Lord and my God. Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed; blessed are they that have not seen, and yet have believed." Thus was the fact of the resurrection established by the evidence of so many of the senses, as to render deception impossible.
21. In some instances the touch itself, is liable to error. For example, if we roll a pea, or a bullet, between two fingers crossed, we receive the impression of two distinct objects, though we know there is only one ; and if we look at it, at the same time, the illusion is not removed, though we see at once that it is an illusion. The organs here are, however, placed in an unnatural position. Another fallacy occurs with respect to heat. If we place the hand in separate vessels, the one containing warm, and the other very cold water, and after some time withdraw the hands, and immediately plunge them in the mixture of both waters, to the one hand the mixture appears warm, and to the other cold. So in a tropical country, if one person descends a high mountain from the regions of perpetual snow, and meets at the middle, another ascending from the hot valley below, he who is descending will feel oppressed with heat, while the other is shivering with cold, and both sensations are produced by the same temperature. Frozen mercury excites the same sensation as red hot iron. A piece of marble will feel colder than a woollen garment, although both be of the same temperature, because the marble is a better conductor of heat than woollen ; a deep cellar appears warm to us in winter, and cold in summer, though its temperature is nearly the same all the year round. During the voyages made by Captain Parry to discover the north west passage, it was found that after having lived for some days in a temperature of 15 or 20 degrees below zero, it felt quite mild and comfortable when the thermometer rose to zero and conversely. The sense, therefore, only gives us an idea of the relative, not the actual heat of bodies.
22. The sense of feeling may become blunted to an extraordinary decree. Chabert, the Fire King, was said to have been in the habit of swallowing forty grains of phosphorus at once ; washing his hands in melted lead ; and drinking boiling oil, without any apparent injury. There is a great difference in the degree of sensibility of the mucous membrane, in different individuals, some being able without inconvenience, to swallow fluids of a temperature which would be very uncomfortable to others.
23. The tactile power of the skin is not proportionate to its sensibility. Thus the arm pits, flanks, soles of the feet, and other parts of the body, have slight power of distinguishing objects by touch, although they are very sensible. It would be difficult to make a person laugh by tickling the ends of his fingers, and yet we have seen that their sense of touch is more delicate than that of any other portion of the skin. All the surfaces and solids of the body possess a kind of sensibility, peculiar to themselves, and in disease may give sensations, but this a different property from that of touch.
What is a sensation ? How are they divided ? What is an internal ? What an external sensation ? What are ideas ? What is the office of the senses ? How many external senses are there ? Are they under the control of the will ? What is touch ? Is touch the same as feeling ? Of how many layers is the skin composed ? What is the cuticle ? How formed ? Its use ? Is it subjected to the same law as the other parts of the body are in relation to pressure ? What would have been the consequence ? Describe the mucous web.-The true skin. Where is the sense of touch chiefly situated ? Describe the papilla?. What is the pulp of the fingers chiefly composed of? Can the blind distinguish colours by the touch ? How is this explained ? Why is the external surface endowed with special sensibility ? What does Majendie say of the human skin ? By what process are the blind enabled to read ? What cases show that the possession of a hand is not necessary for the display of intellect and ingenuity ? What is the organ of touch in animals ?-in insects ? What senses are liable to illusions ? Which is the most certain of the senses ? What fact was established by the senses of hearing, sight, and touch ? Is the touch ever liable to error ? In what cases ? May the sense of feeling become blunted ? What facts prove it ? Are the tactile powers of the skin in proportion to its sensibility ?