Part 11

In this circumstance of their possessing a one-celled heart, and colder and darker blood, they approach to the state of fish; which thus appear not to acquire so much oxygen by their gills from the water as terrestrial animals do by their lungs from the atmosphere; whence it may be concluded that the gills of fish do not decompose the water which passes through them, and which contains so much more oxygen than the air, but that they only procure a small quantity of oxygen from the air which is diffused in the water; which also is further confirmed by an experiment with the air-pump, as fish soon die when put in a glass of water into the exhausted receiver, which they would not do if their gills had power to decompose the water and obtain the oxygen from it.

The lamprey, petromyzon, is put by Linneus amongst the nantes, which are defined to possess both gills and lungs. It has seven spiracula, or breathing holes, on each side of the neck, and by its more perfect lungs approaches to the serpent kind; Syst. Nat. The means by which it adheres to stones, even in rapid streams, is probably owing to a

## partial vacuum made by its respiring organs like sucking, and may be

compared to the ingenious method by which boys are seen to lift large stones in the street, by applying to them a piece of strong moist leather with a string through the centre of it; which, when it is forcibly drawn upwards, produces a partial vacuum under it, and thus the stone is supported by the pressure of the atmosphere.

The leech, hirudo, and the remora, echeneis, adhere strongly to objects probably by a similar method. I once saw ten or twelve leeches adhere to each foot of an old horse a little above his hoofs, who was grazing in a morass, and which did not lose their hold when he moved about. The bare-legged travellers in Ceylon are said to be much infested by leeches; and the sea-leech, hirudo muricata, is said to adhere to fish, and the remora is said to adhere to ships in such numbers as to retard their progress.

The respiratory organ of the whale, I suppose, is pulmonary in part, as he is obliged to come frequently to the surface, whence he can be pursued after he is struck with the harpoon; and may nevertheless be in part like the gills of other fish, as he seems to draw in water when he is below the surface, and emits it again when he rises above it.

ADDITIONAL NOTE. VI.

HIEROGLYPHIC CHARACTERS.

So erst as Egypt's rude designs explain.

## CANTO I. l. 351.

The outlines of animal bodies, which gave names to the constellations, as well as the characters used in chemistry for the metals, and in astronomy for the planets, were originally hieroglyphic figures, used by the magi of Egypt before the invention of letters, to record their discoveries in those sciences.

Other hieroglyphic figures seem to have been designed to perpetuate the events of history, the discoveries in other arts, and the opinions of those ancient philosophers on other subjects. Thus their figures of Venus for beauty, Minerva for wisdom, Mars and Bellona for war, Hercules for strength, and many others, became afterwards the deities of Greece and Rome; and together with the figures of Time, Death, and Fame, constitute the language of the painters to this day.

From the similarity of the characters which designate the metals in chemistry, and the planets in astronomy, it may be concluded that these parts of science were then believed to be connected; whence astrology seems to have been a very early superstition. These, so far, constitute an universal visible language in those sciences.

So the glory, or halo, round the head is a part of the universal language of the eye, designating a holy person; wings on the shoulders denote a good angel; and a tail and hoof denote the figure of an evil demon; to which may be added the cap of liberty and the tiara of popedom. It is to be wished that many other universal characters could be introduced into practice, which might either constitute a more comprehensive language for painters, or for other arts; as those of ciphers and signs have done for arithmetic and algebra, and crotchets for music, and the alphabets for articulate sounds; so a zigzag line made on white paper by a black-lead pencil, which communicates with the surface of the mercury in the barometer, as the paper itself is made constantly to move laterally by a clock, and daily to descend through the space necessary, has ingeniously produced a most accurate visible account of the rise and fall of the mercury in the barometer every hour in the year.

Mr. Grey's Memoria Technica was designed as an artificial language to remember numbers, as of the eras, or dates of history. This was done by substituting one consonant and one vowel for each figure of the ten cyphers used in arithmetic, and by composing words of these letters; which words Mr. Grey makes into hexameter verses, and produces an audible jargon, which is to be committed to memory, and occasionally analysed into numbers when required. An ingenious French botanist, Monsieur Bergeret, has proposed to apply this idea of Mr. Grey to a botanical nomenclature, by making the name of each plant to consist of letters, which, when analysed, were to signify the number of the class, order, genus, and species, with a description also of some

## particular part of the plant, which was designed to be both an audible

and visible language.

Bishop Wilkins in his elaborate "Essay towards a Real Character and a Philosophical Language," has endeavoured to produce, with the greatest simplicity, and accuracy, and conciseness, an universal language both to be written and spoken, for the purpose of the communication of all our ideas with greater exactness and less labour than is done in common languages, as they are now spoken and written. But we have to lament that the progress of general science is yet too limited both for his purpose, and for that even of a nomenclature for botany; and that the science of grammar, and even the number and manner of the pronunciation of the letters of the alphabet, are not yet determined with such accuracy as would be necessary to constitute Bishop Wilkins's grand design of an universal language, which might facilitate the acquirement of knowledge, and thus add to the power and happiness of mankind.

ADDITIONAL NOTE. VII.

OLD AGE AND DEATH.

The age-worn fibres goaded to contract By repetition palsied, cease to act.

## CANTO II. l. 4

I. _Effects of Age._

The immediate cause of the infirmities of age, or of the progress of life to death, has not yet been well ascertained. The answer to the question, why animals become feeble and diseased after a time, though nourished with the same food which increased their growth from infancy, and afterwards supported them for many years in unimpaired health and strength, must be sought for from the laws of animal excitability, which, though at first increased, is afterwards diminished by frequent repetitions of its adapted stimulus, and at length ceases to obey it.

1. There are four kinds of stimulus which induce the fibres to contract, which constitute the muscles or the organs of sense; as, first, The application of external bodies, which excites into action the sensorial power of irritation; 2dly, Pleasure and pain, which excite into action the sensorial power of sensation; 3dly, Desire and aversion, which excite into action the power of volition; and lastly, The fibrous contractions, which precede association, which is another sensorial power; see Zoonomia, Vol. I. Sect. II. 13.

Many of the motions of the organic system, which are necessary to life, are excited by more than one of these stimuli at the same time, and some of them occasionally by them all. Thus respiration is generally caused by the stimulus of blood in the lungs, or by the sensation of the want of oxygen; but is also occasionally voluntary. The actions of the heart also, though generally owing to the stimulus of the blood, are also inflamed by the association of its motions with those of the stomach, whence sometimes arises an inequality of the pulse, and with other parts of the system, as with the capillaries, whence heat of the skin in fevers with a feeble pulse, see Zoonomia. They are also occasionally influenced by sensation, as is seen in the paleness occasioned by fear, or the blush of shame and anger; and lastly the motions of the heart are sometimes assisted by volition; thus in those who are much weakened by fevers, the pulse is liable to stop during their sleep, and to induce great distress; which is owing at that time to the total suspension of voluntary power; the same occurs during sleep in some asthmatic patients.

2. The debility of approaching age appears to be induced by the inactivity of many parts of the system, or their disobedience to their usual kinds and quantities of stimulus: thus the pallid appearance of the skin of old age is owing to the inactivity of the heart, which ceases to obey the irritation caused by the stimulus of the blood, or its association with other moving organs with its former energy; whence the capillary arteries are not sufficiently distended in their diastole, and consequently contract by their elasticity, so as to close the canal, and their sides gradually coalesce. Of these, those which are most distant from the heart, and of the smallest diameters, will soonest close, and become impervious; hence the hard pulse of aged patients is occasioned by the coalescence of the sides of the vasa vasorum, or capillary arteries of the coats of the other arteries.

The veins of elderly people become turgid or distended with blood, and stand prominent on the skin; for as these do not possess the elasticity of the arteries, they become distended with accumulation of blood; when the heart by its lessened excitability does not contract sufficiently forcibly, or frequently, to receive, as fast as usual, the returning blood; and their apparent prominence on the skin is occasioned by the deficient secretion of fat or mucus in the cellular membrane; and also to the contraction and coalescence and consequent less bulk of many capillary arteries.

3. Not only the muscular fibres lose their degree of excitability from age, as in the above examples; and as may be observed in the tremulous hands and feeble step of elderly persons; but the organs of sense become less excitable by the stimulus of external objects; whence the sight and hearing become defective; the stimulus of the sensorial power of sensation also less affects the aged, who grieve less for the loss of friends or for other disappointments; it should nevertheless be observed, that when the sensorial power of irritation is much exhausted, or its production much diminished; the sensorial power of sensation appears for a time to be increased; as in intoxication there exists a kind of delirium and quick flow of ideas, and yet the person becomes so weak as to totter as he walks; but this delirium is owing to the defect of voluntary power to correct the streams of ideas by intuitive analogy, as in dreams: see Zoonomia: and thus also those who are enfeebled by habits of much vinous potation, or even by age alone, are liable to weep at shaking hands with a friend, whom they have not lately seen; which is owing to defect of voluntary power to correct their trains of ideas caused by sensation, and not to the increased quantity of sensation, as I formerly supposed.

The same want of voluntary power to keep the trains of sensitive ideas consistent, and to compare them by intuitive analogy with the order of nature, is the occasion of the starting at the clapping to of a door, or the fall of a key, which occasions violent surprise with fear and sometimes convulsions, in very feeble hysterical patients, and is not owing I believe (as I formerly supposed) to increased sensation; as they are less sensible to small stimuli than when in health.

Old people are less able also to perform the voluntary exertions of exercise or of reasoning, and lastly the association of their ideas becomes more imperfect, as they are forgetful of the names of persons and places; the associations of which are less permanent, than those of the other words of a language, which are more frequently repeated.

4. This disobedience of the fibres of age to their usual stimuli, has generally been ascribed to repetition or habit, as those who live near a large clock, or a mill, or a waterfall, soon cease to attend to the perpetual noise of it in the day, and sleep dining the night undisturbed. Thus all medicines, if repeated too frequently, gradually lose their effect; as wine and opium cease to intoxicate: some disagreeable tastes as tobacco, by frequent repetition cease to be disagreeable; grief and pain gradually diminish and at length cease altogether; and hence life itself becomes tolerable.

This diminished power of contraction of the fibres of the muscles or organs of sense, which constitutes permanent debility or old age, may arise from a deficient secretion of sensorial power in the brain, as well as from the disobedience of the muscles and organs of sense to their usual stimuli; but this less production of sensorial power must depend on the inactivity of the glands, which compose the brain, and are believed to separate it perpetually from the blood; and is thence owing to a similar cause with the inaction of the fibres of the other parts of the system.

It is finally easy to understand how the fibres may cease to act by the usual quantity of stimulus after having been previously exposed to a greater quantity of stimulus, or to one too long continued; because the expenditure of sensorial power has then been greater than its production; but it is not easy to explain why the repetition of fibrous contractions, which during the meridian of life did not expend the sensorial power faster than it was produced; or only in such a degree as was daily restored by rest and sleep, should at length in the advance of life expend too much of it; or otherwise, that less of it should be produced in the brain; or reside in the nerves; lastly that the fibres should become less excitable by the usual quantity of it.

5. But these facts would seem to show, that all parts of the system are not changed as we advance in life, as some have supposed; as in that case it might have preserved for ever its excitability; and it might then perhaps have been easier for nature to have continued her animals and vegetables for ever in their mature state, than perpetually by a complicate apparatus to have produced new ones, and suffer the old ones to perish; for a further account of stimulus and the consequent animal exertion, see Zoonomia, Vol. I. Sect. 12.

II. _Means of preventing old age._

The means of preventing the approach of age must therefore consist in preventing the inexcitability of the fibres, or the diminution of the production of sensorial power.

1. As animal motion cannot be performed without the fluid matter of heat, in which all things are immersed, and without a sufficient quantity of moisture to prevent rigidity: nothing seems so well adapted to both these purposes as the use of the warm bath; and especially in those, who become thin or emaciated with age, and who have a hard and dry skin, with hardness of the coat of the arteries; which feels under the finger like a cord; the patient should sit in warm water for half an hour every day, or alternate days, or twice a week; the heat should be about ninety-eight degrees on Fahrenheit's scale, or of such a warmth, as may be most agreeable to his sensation; but on leaving the bath he should always be kept so cool, whether he goes into bed, or continues up, as not sensibly to perspire.

There is a popular prejudice, that the warm bath relaxes people, and that the cold bath braces them; which are mechanical terms belonging to drums and fiddle-strings, but not applicable except metaphorically to animal bodies, and then commonly mean weakness and strength: during the continuance in the bath the patient does not lose weight, unless he goes in after a full meal, but generally weighs heavier as the absorption is greater than the perspiration; but if he suffers himself to sweat on his leaving the bath, he will undoubtedly be weakened by the increased action of the system, and its exhaustion: the same occurs to those who are heated by exercise, or by wine, or spice, but not during their continuance in the warm bath: whence we may conclude, that the warm bath is the most harmless of all those stimuli, which are greater than our natural habits have accustomed us to; and that it

## particularly counteracts the approach of old age in emaciated people

with dry skins.

It may be here observed in favour of bathing, that some fish are believed to continue to a great age, and continually to enlarge in size, as they advance in life; and that long after their state of puberty. I have seen perch full of spawn, which were less than two inches long; and it is known, that they will grow to six or eight times that size; it is said, that the whales, which have been caught of late years, are much less in size than those, which were caught, when first the whale-fishery was established; as the large ones, which were supposed to have been some hundred years old, are believed to be already destroyed.

All cold-blooded amphibious animals more slowly waste their sensorial power; as they are accustomed to less stimulus from their respiring less oxygen; and their movements in water are slower than those of aerial animals from the greater resistance of the element. There besides seems to be no obstacle to the growth of aquatic animals; as by means of the air-bladder, they can make their specific gravity the same as that of the water in which they swim. And the moisture of the element seems well adapted to counteract the rigidity of their fibres; and as their exertions in locomotion, and the pressure of some parts on others, are so much less than in the bodies of land animals.

2. But as all excessive stimuli exhaust the sensorial power, and render the system less excitable for a time till the quantity of sensorial power is restored by sleep, or by the diminution or absence of stimulus; which is seen by the weakness of inebriates for a day at least after intoxication. And as the frequent repetition of this great and unnatural stimulus of fermented liquors produces a permanent debility, or disobedience of the system to the usual and natural kinds and quantities of stimulus, as occurs in those who have long been addicted to the ingurgitation of fermented liquors.

And as, secondly, the too great deficiency of the quantity of natural stimuli, as of food, and warmth, or of fresh air, produces also diseases; as is often seen in the children of the poor in large towns, who become scrofulous from want of due nourishment, and from cold, damp, unairy lodgings.

The great and principal means to prevent the approach of old age and death, must consist in the due management of the quantity of every kind of stimulus, but particularly of that from objects external to the moving organ; which may excite into action too great or too small a quantity of the sensorial power of irritation, which principally actuates the vital organs. Whence the use of much wine, or opium, or spice, or of much salt, by their unnatural stimulus induces consequent debility, and shortens life, on the one hand, by the exhaustion of sensorial power; so on the other hand, the want of heat, food, and fresh air, induces debility from defect of stimulus, and a consequent accumulation of sensorial power, and a general debility of the system. Whence arise the pains of cold and hunger, and those which are called nervous; and which are the cause of hysteric, epileptic, and perhaps of asthmatic paroxysms, and of the cold fits of fever.

3. Though all excesses of increase and decrease of stimulus should be avoided, yet a certain variation of stimulus seems to prolong the excitability of the system; as during any diminution of the usual quantity of stimulus, an accumulation of sensorial power is produced; and in consequence the excitability, which was lessened by the action of habitual stimulus, becomes restored. Thus those, who are uniformly habituated to much artificial heat, as in warm parlours in the winter months, lose their irritability in some degree, and become feeble like hot-house plants; but by frequently going for a time into the cold air, the sensorial power of irritability is accumulated and they become stronger.

Whence it may be deduced, that the variations of the cold and heat of this climate contribute to strengthen its inhabitants, who are more

## active and vigorous, and live longer, than those of either much warmer

or much colder latitudes.

This accumulation of sensorial power from diminution of stimulus any one may observe, who in severe weather may sit by the fire-side till he is chill and uneasy with the sensation of cold; but if he walks into the frosty air for a few minutes, an accumulation of sensorial power is produced by diminution of the stimulus of heat, and on his returning into the room where he was chill before, his whole skin will now glow with warmth.

Hence it may be concluded, that the variations of the quantity of stimuli within certain limits contribute to our health; and that those houses which are kept too uniformly warm, are less wholesome than where the inhabitants are occasionally exposed to cold air in passing from one room to another.

Nevertheless to those weak habits with pale skins and large pupils of the eyes, whose degree of irritability is less than health requires, as in scrofulous, hysterical, and some consumptive constitutions, a climate warmer than our own may be of service, as a greater stimulus of heat may be wanted to excite their less irritability. And also a more uniform quantity of heat may be serviceable to consumptive patients than is met with in this country, as the lungs cannot be clothed like the external skin, and are therefore subject to greater extremes of heat and cold in passing in winter from a warm room into the frosty air.