EX LIBRIS BARNES WOODHALL ¥ . ** . ■. - . Z O O N O M I As the laws O F ORGANIC LIFE. ZOONOMIAs . O R THE LAWS O F ORGANIC LIFE. VOL. I, By ERASMUS DARWIN, M. D. F. R. S. AUTHOR OF THE BOTANIC GARDEN. Principid coelum, ac terras, camposque liquentes, Lucentemque globum lunae, titaniaque astra, Spiritus intus alit, totamque infusa perartus Mens agitat molem, et magno se corpore miscet. Virg. JE n. vi. Earth, on whose lap a thousand nations tread, And Ocean, brooding his prolific bed, Night’s changeful orb, blue pole, and silvery zones, Where other worlds encircle other suns, One Mind inhabits, one diffusive Soul Wields the large limbs, and mingles with the whole. NE TV- YORK: Printed by T. & J. SWORDS, Printers to the Faculty of Phylic of Columbia College, No. 99 Pearl-Street. . JlW K 1 ** r-U) > r-i m 4 ’ ' •• DEDICATION. To the candid and ingenious Members of the College of Phyficians, of the Royal Philofophi- cal Society, of the two Univeriities, and to all thofe who ftudy the Operations of the Mind as a Science, or who pradlife Medicine as a Pro- feffion, the fubfequent Work is, With great refpedl, Infcribed by THE AUTHOR. Derby, May i, 1794. CONTENTS Sect. I. II. III. IV. V. VL VII. VIII. IX. X. XI. XII. XIII. XIV. XV. XVI. XVII. XVIII. XIX. XX. XXL XXII. XXIII. XXIV. PREFACE to the American Edition. Lines to Erafmus Darwin. Author’ s Preface. Of Motion. Explanations and Definitions. The AAotions of the Retina demonf rated by Experiments. Laws of Animal Caufation. Of the four Faculties or Motions of the Sen- forium. OJ the four Clajfes of Fibrous AAotions. Of Irritative AAotions. Of Scnftive AAotions. Of F oluntary AAotions. Of Affociate AAotions. Additional Obfcrvations on the Senforial Powers. Of Stimulus , Senforial Exertion, and Fibrous Contraction. Of F egetable Animation. Of the Production of Ideas. Of the Clafjes of Ideas. Of InJlinCt. The Catenation of Animal AAotions. Of Sleep. Of Reverie. Of Fertigo. Of Drunkennefs. Of Propcnfity to AAotion. Repetition, Imi- tation. Of the Circulatory Syfem. Of the Secretion of Saliva, and ef Tears. And f the Lacrymal Sack. Sect. CONTENTS. Sect. XXV. XXVI. XXVII. XXVIII. XXIX. XXX. XXXI. XXXII. XXXIII. XXXIV. XXXV. XXXVI. XXXVII. . XXXVIII. XXXIX. XL. Of the Stomach and Intejiines. Of the Capillary Glands , and of the Mem- branes. Of Haemorrhages. The Paralyfes of the Laffeals. The Retrograde Motions of the Abforbent V tffels. The Paralyfs of the Liver. Of Temperaments. Difeafes of Irritation. • of Senfation. of V olition. of Affociation. The Periods of Difeafes. Of Digeflion, Secretion , Nutrition. Of the Oxygenation of the Blood in the Lungs and Placenta. Of Generation. Of Ocular Speflra. PREFACE PREFACE TO THE AMERICAN EDITION. In the progrefs of cbfervaticn and experiment in phyfics, within a few years, fuch a number of new and important facts have been brought to light, that many philofophers have believed the people of the pre- fent day were polTefred of a great deal more know- ledge than the moderns of the three laid centuries, or their ancient predeceffors. This opinion, in particular, has been deemed well founded, and true in its refpedt to medicine, which, at this time, is not only confidered fufceptihle of new ex- pofitions and interpretations, but of being greatly im- proved and enlarged, both in theory and practice. And although among thofe who think thus are reck- oned molt of the original and clear-lighted geniufes of cur time, yet there are not wanting fome, and thofe men of talents and reputation too, who are in the ha- bit of thinking, if the ancients knew not quite as much as ourfelves, yet their writings contain the leading hints, or great outlines of almofc every thing difcover- able, either diredtly expreued, or fignified in allegori- cal terms. This literary fuperftition 'has been carried a great way ; and if it had flopped at declaring the Iliad the bell of poffible poems, or the Philiipics the moft finished of the rhetorical productions, I fhouldnot at this time have troubled myfelf to contradict it. But when thefe enthufiafsic admirers of antiquity declare, that, in matters of lcience as well as of letters, the fubjedts of enquiry have been exhaufted two thoufand years ago, a and X PREFACE TO THE and that no idea can be Farted which is not an imita-* tion of fomething that a Greek or a Roman, or fome body elfe, had thought before, I own I am a little dif- pofed to believe their alfertions are grounded neither in truth nor in the nature of things. For why muft we refort to the Platonists, Stoics, and Peripate- tics, for doctrines which the A c a d e m y , the P o r c h, . and the Lyceum never knew? Thefe remarks are made in confer uence of an opi- nion propagated and believed by fome, that a certain method of reafoning upon medical lubjbts, and of p raft i ling phytic, introduced now of late, as many be- lieve, which is already pretty well efLbiifhed, and ac- quiring rapidly more and more adherents, is in fact but a revival and new-modelling of the opinions and pro- cedure of the Methodic Sect, founded by Ascle- Piades, the cotemporary of Mithridates and Crassus. In order to know whether this opinion is w r ell found- ed, I fnall enquire what the philo fophy of the Metho- dic Sect was. Its founder, Asclepiades, adopted that philofo- P b -y> whofe foundation had been laid by Anaxago- ras, Empedocles, and Heraclitus, and which was afterwards wrought up into the Atomic Syjiem, by Leucippus, and Democritus, of the Eieatic Sect, who, rejecting ail metaphyhcal explanations of the caufes of things, undertook the interpreting nature, from the laws of matter and motion. This was af- terwards commented upon, enlarged, and adorned by Epicurus, lb as to form, what was afterwards called the Epicurean PhilofopJiy. What the details of this are, may be leen in Diogenes Laertius, in Brucker, and his tramlator En f i e l d, as well as in the poem of Lucretius, who has confeifedly attempted a poetical display of thefe very doctrines. A general view, comp riling a mere lkctch of the fyftem of this Ay]ojjio#j£jo; as far as connected with the prefent fubject, is AMERICAN EDITION. XI is all I fhall offer here. An Epicurean would explain himfelf thus: — £C It is clear, from the changes which natural bodies undergo, that there is a perpetual for- mation and deftruction of them going on ; there muft then exift matter of which thefe things are formed, -and into which .they are refolved ; and hence proceeds the conclufion which is the ground-work of the fyftsm, that a thins can neither be made out of nothin?, nor reduced to nothing. ‘ Nullam r.em e nihilo gigni divi- nitus unquam The .univerfe, therefore, as to its con- ftituent atoms or particles, was always as it is at pre.- fent j and confequently matter is eternal. The work- man cannot perform any thing without materials ; and thefe felf-exiftent materials, in. the decay and renova- tion they undergo, account for .the phenomena of na- ture and of art. If things were created out of nothing, then every kind {liquid proceed from each, and the greate'ft irregularity enfue; men fhould be produced in the lea, fifties on the land, and cattle in the clouds ; generation would be ufelefs,' and food unneceftary : if they returned to nothing, then, in the courfe ofpaft ages, through wafte, oonfumption, and lofs, much muft have vanifhed to non-exiftence, and have been completely annihilated. But neither of thefe fuppofitions is true, lince, out of the wreck or ruin of one being; or exift- ence, nature, we know, without an aft of creation or annihilation, can work up the old materials into a new fabric. “ All exiftences in nature are referable to two kinds, i . Bodies ; and, 2. The inane, or void in which they exift. “ Our fenfes fatisfy us of the exiftence of bodies, as alfo do their actions paftions, and refitting powers ; par- ticularly as they operate upon each other, and upon our touch : “ Tangere enim et tang! nisi corpus nulla potest res.” “ From the exiftence and motion of bodies is in- ferred the exiftence of fpace ; and the effedt of bodies operating upon each other is denominated “ an event ■” and PREFACE TO THE xii and if there was not. a void there would not be a poflibility of motion ; for if a plenum exifted, then every portion of fpace being clofety impacted and wedged with folidity, the moft uniform reft and dead ftilliiefs would pervade the whole of nature. “ As to bodies, they either confift of elementary atoms, or of fubftances formed from thefe; and theie primordial particles, notvvith ftanding foms appearances to the contrary, are fimple, iolid, and inaivifible. “ Sunt igitur solida, ac sine inani corpora prinna.” “ All thefe atoms' poffefs the fame general proper- ties, and do not differ from each other in arm eftential refpeft. Though, from their different operations up- on the fenfes, is inferred a difference among them as to lize, fftape, and heayinels. Their figures, in parti- cular, are varied in an endiefs manner, io as to take on every mechanical form; but in all thefe cafes they are ftiil infrangible and incapable of farther diviiion. “ Each atom contains, within itfelf, an active energy, or internal force, by which it is either conftantiy in motion, or making an effort to move ; and this is de- nominated gravity. Thefe atoms, impelled by gravity through void fpace in curvilinear courles, it.' ike again ft each other, exercife repelling powers, and produce vi- bration or agitation ; and as this gravitating power is eftential to matter, it can never be inactive, but muft be always at work., and has been fo from eternity. “ Every compound body, being made up of indivi- dual atoms, therefore poffeffes the united energy of them all, which energy is the foie agent in nature; but by reafon of their different figures, their varied magni- tudes, and particular fituations, it is varioufly modifi- ed ; as when the atoms are hooked or rough, motion will be retarded among them, and be facilitated when they are round and fmooth, as in the principles of fire and animation. Bodies thus being; comooted of atoms, derive their adhons from the energy inherent in and proceeding from thefe atoms. ‘ Adi AMERICAN EDITION. xiii “ All alterations happening in bodies, whether in their- fhape, hardnefs, iweetnefs, &c. are afcribable to the change taking place in the arrangement, difpofi- tion, &ct of the' confiitnent particles ; and thus poro- hty, transparency, elafticity, malleability, &c._ are to be accounted for in the fame way. Gravity being an effential property of matter, all corpufcules, and all bodies formed of them, muft be heavy. “ Thus, horn thefe properties of bodies, their feve- ral combinations and mechanical operations, arife other more complex phenomena, referable however to the principle of motion, fuch as the heating of bodies from the influx of loft, round and fmooth particles ; the cool - ing of them from the ingrefs of atoms of oppolite and ir- regular figures ; even fenfaticns, both of the plealureable and painful kinds, motion, reft, and time itfelf, are con- tingences to bodies. In lhort, the whole phenomena of the production, growth, nutrition, decline, and dif- folution of bodies, is to be afcribed to an alteration of arrangement in the particles, and to their addition or iftbft raction. “ Minerals, plants, and animals were thus produced m the beginning, according to thefe mechanical laws of matter and motion, and fo was the world they comppfe and inhabit. They continue to propagate their kinds in regular ways, becaufe nature has become accuftcm- ed, by habit , to produce them in an order fo uniform as to look like delign. The eye, however, was not made for feeing, nor the ear fpr hearings but having been accidentally formed in fuch a way as to anfwer thefe pur'pofes, the fentient principle within, which is co-ex- iftent with the organization, finding them fit for the purpofes of fight and hearing, makes ufe of them ac- cordingly. “ Senfation, proceeding from the arrangement and texture of particles, is to be aicribed to their peculiar magnitude, fnape, combination, &c. fo that inftead of being an original property of matter, it is, in fadt, only an XIV PREFACE TO THE an occasional quality. Death is the privation of fenfa- tion, in confequence of the feparation of the fentient principle from the body : and this fentient principle, when a man dies, is decompounded into its Ample atoms, lofes its fenfitive powers, and goes into other forms and combinations. The foul, in this refpect, re- fembling the e)^e, which is no longer capable of per- forming its functions than the connection of its or- ganized texture with the body lafts.” What Asclepiades did, was to apply the princi- ples of the Epicurean Philofophy to medicine, and this he did with much ingenuity and acutenefs. Building upon that hypothefis, he fuppofed the human body compofed of Epicurus’ ultimate atoms, which, by their figure, proximity, and arrangement, enabled it to per- form its functions; and in a particular manner, that health con fifed in the fymmetry and permeability of certain paftages through the firm parts, which he called pores j and the doling up, or obstruction of thefe, confti- tuted difeafe. He imagined the fluids to be formed of particles, varying in figure and fize, and thus making all the varieties of them, from the thickeft blood to the moft attenuated animal fpirits. And when thefe fluids moved freely through their pores, the body was found ; but when they were too narrow, fo as to pro- duce ftagnations, or fo oblique as not to be readily paflable, then indifpofi tion enlued. Such were the leading principles of Asclepiades, and he had many followers, among whom Themison of Laodicea was the moft eminent. He rejected moft of the fubtle and laboured reafonings of his mafter, and, declaring fuch minute inveftigations were ufelels, affirmed, without defending to particulars, and bur- thening himfelf with details, a phyfician need only make himfelf acquainted with the general principles of dif- eafes. Thefe, he faia, all belonged to two clafles. i. Thofe proceeding from laxity and, 2. Such as were caufed by fcnciure. All that was neceflary to be done, therefore, AMERICAN EDITION. xv therefore, was to afcertain to which clafs any given difeafe belonged ; and then, if to the former, to pre- fcribe afiringent ; if to the latter, relaxing remedies. The regular and fyftemaiic plan which Themison and his numerous followers adopted in their practice, differing very widely from the conjectural and uncertain, mode of other phyficians, cauled them to be called Methodists ; and they are to this day known in hif- toryby the name of the Methodic Sect. While Themison was reflecting upon his fyftem, and endea- vouring to advance it to maturity, he died, and the un- finifhed work was taken up and completed by his fol- lower Thessalus. He lived in the time of N e r o ^ and having rejected, as frivolous, all the opinions of his predeceflors, he declaimed, with vehemence and fury, againft the phyficians of all ages, and offered to inftruCt a beginner in the art of medicine in the fhort duration, of fix months. He, with a degree of arrogance and impudence, of which, as no parallel is known to have exifted in ancient times, it can only be found in the hiftory of modem quackeiy, took upon himfelf the appellation of or the conqueror of phyfi- cians. After Thessalus the feCt began to decline and dwindle, and although Soranus, Julian, and Moschion retarded for a while its downfall, yet it was totally abforbed and loft in the Galenic Doctrines which followed. Thus, from an examination of the Methodic SyJlern , it is evident the explanation of every thing in the ani- mal economy is attempted upon principles of me- chanism only. The firft notice of any thing elfe requifite to give life, and regulate its functions, teems to have occurred to Hippocrates, the cotemporary of Democritus and Leucippus. The TO EVOffjLUy of thi-s fagacious ob- ferver, as the interpretation of the word imports, ob- vioufly means an exciting power in animals : and the effeCts xvl PREFACE TO THE effe&s of animation refultirig ffbrri this, imperfectly known, and badly explained, doubtiefs give rife, ac- cording to the opinion and judgment of the different writers, to the Nature of Sydenham,* the Aura Vi- tal is of Van He l mo nt, - f the Vis natures Medicatrix of G A u b i us,'.j; the Amnia Medico, of Stahl and Nichols,^ and the learned and curious treatife, enti- tled Imp'elum Faciens , of Kaauw Boerhaave.J! And here it is worthy of remark, that from Hip- pocrates to Brown, all writers entertain the opi- nion of a principle or power within, exifting as the caufe of life, as appears by the adtive fignificaiion of all their terms ; whereas the idea of the Brunbnians is, that the organized animal iolid poifelTes no internal energy, and would always remain inactive, uhiefs excited by ftimuli from without ; they therefore fpeak of cue vi- tal capacity in the pajjive voice, as fuiceptible of being acted upon. Herman Boerkaavs, in his account of the dif- eafes of a lax and of a rigid fibre, feems again to relapfe into the mechanical confederation of thefe things; but Haller, by his numerous and luminous experiments on fenfibility and irritability, led the way to a right mode of purfuingand underftanding fuch enquiries. The attention of Hoffman had been turned to the confideration of the nervcus fyftem, as influencing dif- eafes, more particular than any other perfori ; and from his writings were probably taken the hints which ter- minated in Cullen’s doftrine of Excitement and Col- lapse y in his Phyiiological Tract ;4f[ enlarged afterwards, and * Opera Passim. f Equidem sciant Splritum esse aliquem illud imjietum faciens Mifipocrates , vitas clavum nsanu sua tenens (Ort. Medicin. p. 724.) ■j Who quotes Hippocrates for the idea (Sect. 649.) couched under the term of «i/!o*fa?s*-as. § Animam esse Gubernatricem, &c. &c. Oratio de anima Medica. passim. || Lug. Batav. Luchtman’s, 1745. (Chap. 2.) «j[ Institutes of Medicine, § 126 to 135. “ From what has been now said of the excitement and collapse of the brain, it will ap- AMERICAN EDITION. XVII and applied to practice, in his chapter on vefarike, (Firft Lines, § r 544. and feq.) as well as the obferva- rions in his letter on the recovery of perfons drowned : (p. 4.) “ Though the circulation of the blood is necef- fary to the fupport of life, the living fcate of animals does not confift in that alone, but efpecially depends upon a certain condition of the nerves and mufcular fibres, by which they are fenfible and irritable, and upon which the adlicn of the heart itfeif depends,” See. And alfo the remarks on the effect of ftimuli in keeping up the adtion and energy of the brain* at all times, in his treatife upon the materia medica. John Hunter had been fpeculating too on this fubjedt. In his experiments on animals, with refpccl to their power of producing heat, he has brought curious and important facts to view : though his reafoning on them is in fome inftances inccnclufive and exceptiona- ble, in others quite unphilofophical. This enquiry was intended as a counterpart to the experiments of Blag- den, and his affociates in the heated chamber, on the power of the human body to produce cold in high temperatures. He afcribes a great deal, throughout his performance, to the ftimulant action of cold, and to the exhauftion of the whole of the powers of life in freezing animals, by their efforts to produce heat ; he even afcribes the attempt of his poor vidtim, the dor- moufe, to get cut of the veffel in which he was to be frozen to death, to the roufing of animal adtion by cold! He feems to take little notice of the vital organs, the fire-place whence the confiitution receives its warmth ; nor regard much the condition of the refpiratory func- tion in any of the creatures he operated upon, nor the pain they endured, and the changes in their economy confecuent upon it. The experiments on the egg, b frog, pear that we suppose life, as far as it is corporal, to consist in the ex- citement of the nervous system, and especially of the brain, which unites the different parts, and forms them into a whole.” § 136. * Materia Medica, p. 67, &c. Sviii PREFACE TO THE frog, eel and fnail, may be as well explained on the idea of the increafed fufceptibility of impreffion, pro- duced by the fubduCtion of ftimuli, and by an extra- ordinary exertion of the refpiratory organs caufing a greater evolution of heat, as upon the author’s hypo- thecs, which may be fummoned up in this general eonclufion ; that cold produces its effect in fufpending the voluntary actions,, by acting as a fedative to a cer- tain point ; beyond which it feems to act as a JiimuJant , exciting the animal powers to exert themfeives for felf- prefervation. It will be evident to him who reflects on what has- been related, that the Epicurean Sectaries en- tertained no other than mechanical notions concerning the production, actions, and changes of bodies; and that Hippocrates and his followers, though confi- derably more advanced towards the truth, had gone no farther than to obferve folitary and individual tacts, ar- range thefe into detached fentences, or infulated apho- rifms, fometimesintirely true,. and fome containing only a mixture of truth ; or frame ftrange and whimfical hypothefes, by aid ot which, as general principles, they attempted to explain things ; and the molt forward of them feems to have done little more than trace the cor- poreal functions, by partial induction, to the aio-S»P f -is» zafio \iKov Or COMMON SENSORY. . Such was the condition of medical fcience, until nearly twenty years ago, when, in that very place where fpcifm , reaction, and vis medicairix nature were flourifh- ing in full vigour, under the affiduous cultivation of Cullen, they were nipped and cropped in the blof- fom, and nearly eradicated as noxious, by the improv- ing hand of Brown. From the intimate acquaint- ance which Brown, or Bruno, as he called himfelf, had with the publifhed writings, and probably with the private opinions of Cullen; from his academic habits, his erudition and knowledge of every thing palling at the Univerfity of Edinburgh, he muff have AMERICAN EDITION. xix have had great opportunities, as well of learning all that was printed in phyfic, as of fludying the de- feds, and detecting the weaknefs of that profeffor’s dodrines. He told the writer of this preface, that he ventured one day to talk to Cullen on the incom- prehensible ideas of atony and fpaim exiding in the fame veffels of .the body at the fame time, and thereby provoked him to manifefl figns of impatience and dif- pleafure. A’coolnefs took place immediately, which increafed at laft, by fuccefiive and mutual aggrava- tions, to rooted averfion and deep opposition. And to this irritated date of Brown’s mind, indignant with a fenfe of unbecoming treatment, is to be afcrib- ed no fmall portion of that refolution and energy with which he laboured out a Sydem of Medical Philofo- phy, which, though not free from errors, borrows, however, none from Cullen. On the publication and contents of the fird edition of the Elementa Medicinas of this author I lhali be a little particular, on account of the fcarcity of the work, and of the gratification it may afford to an enquiring mind to learn the progrefs of ufeful difcoveries. It was published in 1780, and was dedicated to Sir John Elliot; but this dedication was withheld from the fecond edition. After dating his twenty years labour in learning and teaching phyfic, he obferves, it was not until the fourth ludrum that fome dawning of light broke in upon him. The opinion that in the phlegmafire of nofologids, local affedtion was not the caufe of pyrexia, but, on the contrary, a fymptom confequent upon a previous general excitement of the whole conditution, appears to have been early adopted by him ; and from his own perfonal fufferings in eryfipelas, cynanche tonfillaris, catarrh, and fynocha, and from his perufal of what- ever had been written by Morgagni, Triller, and other candid authors on thefe fubjedts, and on pneu- monia, he was confident his idea was right. He, XX PREFACE TO THE He, at this time, propofed the doctrine of cold pre- diipofing the body to be operated upon in a pc .verful * manner, and to a morbid degree, by fubfequent her : ; which, indeed, may be regarded as one of the mofi important practical truths in medicine. Pie calls in queftion the propriety of forming opi- nions of the nature of difeafes by their iyrnptoms mere- ly, and boldly adopts the method of judging from the “ Iredentia and juvantia." He offers well-founded criticifm on nofological a:- o _ _ rangement, and fhews wherein, through want of dii- tmdtion between univerfal and local difeafes, a number of thefe had been claffed wrong. On examining the phlogiftic exanthemata he con- tends, that in mealies and fcarlet fever, as well as in fmali-pqx, the general indication of cure is to dimi- nilh the inflammatory diathefis, without the leait re- gard to the particular nature of the contagion, or the ilage of eruption; but thefe are carefully to be diilin- guilhed from the plague, and other eruptive diieaies of a totally oppofite character: and that without at- tending to the peculiarity of the refpiration, or the pre- cife nature of the morbific caufe, the certain things to be attended to are, How far the difeafed condition de- viates from health ; and in wlut degree the living body appreximates towards death. The exanther, '.atom fymptoms in the two clafies of complaints, varying in each, their form only, and not their nature. Having proceeded thus far, lie declares that difeafes of the fame type or clafs arc to be relieved, or cured, by the fame mode of treatment; and that the volumes of diagnostics, and the endleis distinctions of nol'ologv, in fpite of the authority of even Baglivi and Sy- denham, when opoofed to clear reafon and matter of fact, ought to be ciifregarded. He expreffes his an- prehenfions too, left the infinite diftindtion ot diieaies lhould lead to a mode of practice equaliv diverfified, and have a very baneful effect upon materia medica and preferiptions. In AMERICAN EDITION. xxi In his remarks upon predifpofition to bad health, he avers that no perfon ever fuddenly became tick, but that gradually a predifpofition was created by the agen- cy of the exciting powers, and out of this predifpofi- tion grew the difeafe. Of this he gives examples in the phlogiftic exanthemata, wherein he lays, a high degree of excitement produces the difeafe, a lower pre- difpofition, and a {till lower health : the means, there- fore, conducive to the latter of thefe he thinks fo fim- ple, that the ufe of the common ncfology is intirely fuperfeded. Proceeding upon this plan, he diftinguifhes local from univerfal ailments ; both of which are confufediy claffed together, in the different nofological arrange- ments. This led him to an examination of hemorrhagy, which, if attended in the beginning with phlogiftic diathefis, he thought always became eventually afthe- nic, and in this enquiry it was that he was induced to call in queftion the exiftence ot plethora, as a caufe of hemorrhagy, and to rejecft altogether the notion of a vis medicatrix naturre as an agent in the animal fyftem. This firft edition of the Eiementa is an unfinifned work, and comprehends the details of his doftrine no farther than the fihenic form of difeafes. Among thefe he there ranks hemorrhagy, efpecially menorrhagia, hrermorhois, epiftaxis, and apoplexy ; an arrangement which he afterward confidered wrong, and altered ac- cordingly in the following editions, by placing them all in the afthenic clafs. Such, he tells us, was the train of ideas pafiing in his mind as he refledted upon the animal economy ; and upon thefe confiderations did he judge himfeif war- ranted in undertaking an explanation of the fubject, different in many refpects from any thing done before him. Ke declares, throughout the whole, he never de- fcends beneath his dignity to animadvert uoon particu- lar xxii PREFACE TO THE lar per Jons ; though in certain cafes, where almoft im- plicit faith and idolatrous reverence had been given to certain authors, he Iras freely attacked and refuted their opinions. Fie apologizes for the plainnefs of ftile and manner with which the performance is written, efpe- cially, fmce to avoid the contagion of opinion, he had read no medical book for five whole years, and had fcarcely confulted the monuments of ancient elegance for twenty. There is a great deal of animation and force in his argument againft plethora, from the ninety-fourth to the ninety-eighth feCtion, which he concludes with this challenge : “ Si fit quod ad hoc refpondeas, re- fponde Stahli aut jube Junckerum.” In the hundred and fourth fection he oppofes, in de- cided terms, the tonic or aftringcnt operation of cold, particularly as caufing conftriction of the fkinj and repeats the fame in feveral places, (§ 18c — 182.) de? nying that it afts as a ftimulant. In his reafoning againft lentor in the fluids as a caufe of difeafe,. he breaks cut into the following fpirited exclamation : “ Quam infelix ea pathologia eft ! cuius perpetuum principium, quod univerfis ccmprehenfis partibus convenire, univerfas illuflrare, ct explicare debet, ne uni quidern convenit, unam illuftrat, unara explicat, contra omnibus repugnat, omnes obfcurat, et confundit and, rejecting the pathology of th.e fluids, declares, that cool water, pure air, wine, and Peruvian bark refill putrifadlion in no other way than by keeping up excitement. In his remarks upon fpafm, he endeavours to (hew that it cannot be a caufe of difeafe, either of the fthe- nic or aflhenic kind, and ought, of courfe, to be re- jected from both, as fhould alfo what has been called the reaction of thefyjlem , in fever. In the courfe of his animated argument, he afks if, toward the end of the eighteenth century, “ quis, opinionem meram, nulla rationis, nulla veri vel tenuifiima umbra commenda- tam, AMERICAN EDITION. xxiii ram, folidiffimis arguments, item ipfi tuercfe adhibitis compertam falfam, poftvanam omni falfer logics genere defenfionem, pro re vera et certa oblatum iri crederet r” He is eveiy where oppofed to that clafiification and arrangement of difeafes which has lb much obtained of late, and clofes this work with the words, “ Nofo- logia delenda.” He publMhed a fecond edition in the year 1784, and added thereto the afthenic clafs of difeafes. Taught, by experience and obfervation, in the dif- ferent forms of the gout and afthma, of the benefit of ftimulant remedies, he had no hefitation to confider them among the effects of weaknefs ; as were likewife fevers ftridtly fo called (febres) both intermittent and continued, and all the kinds of hemorrhagy, &c. In fhort, the confideration of the difeafes not belonging to the fthenic clafs, convinced him they muff be re- ferred to the afthenic ; fuch were all fpafmodic or con- vulfive ailments, dyfpepfia, and other the like affec- tions of the alimentary canal, and the greater part of the maladies of children. In this performance too, he contends againft the advocates for fedatives. Opium, he declares, has a fti- mulant operation ; colds or catarrhs are produced by heat fucceeding to cold, and not vice verfa j and ex- tends his laws of animation to the vegetable creation. In fhort, he concluded there was in the medullary- nervous matter, and mufcular folid of living bodies, which have been generally called the nervous fyftem, a property by which they could be affected by outward agents, as well as by their own functions, in fuch a way as to produce the phenomena peculiar to the liv- ing ftate. This capacity of being adted upon is term- ed excitability , and the agents are all denominated Jlimulants, while the effect produced by the operation of ftimulants upon excitability is called excitement. Excitement is terminated in two ways. 1. By the exhauftion of excitability, through the violence or con- tinuance- PREFACE TO THE xx iv tinuance of ftimulus, which is called indirect debilii). 2. By the accumulation of excitability, through defi- cient ftimulus, which is termed direct debility. Be- tween the two extremes of indirect and diredt debility are experienced both health and difeafes of the fthenic kind, or thofe febrile complaints (pyrexim,) accom- panied with what has been called phlogiftic diathefls, wherein, though the excitement confiderably exceeds the healthy rate, ftill it does not reach the limits ot indiredt debility. Stimuli lofe their efficacy after long and frequent ap- plication ; but even then the excitability, exhaufted in relation to one ftimulus, is capable of being added upon by another. Therefore, the wafte of excitability, after exhaufticn of one ftimulus after another, is very hard to be re- paired, by reafen of the difficulty of accefs to frefin ftimuli to work upon the languifhing excitability; which, by being applied ftrong at firft, and gradually weakened aftenvards, anfwers the purpofe; and alio the fuperabundant excitability left by mbdudtion of one ftimulus after another, produces fuch an excitable condition of the fyftem, that much nicety is requiiite to wear it gradually away by application of very weak ftimuli at firft, and by degrees ftronger and ftronger, until the accuftomed ones can be comfortably borne. According to the Brunonian Doctrine difeafes appear under various modifications, as exhibited in the tabic below'. T hus they may be, 1 . Univerfal, fuch as primarily affect the whole conftitution, as fevers, &c. 2. Local, where, from limited morbid affedtion, a particular part labours, without difordering the intire habit ; as trifling wounds, phlegmons, See. 3. Loco-uni verfal, when, from a local affection, the whole body is eventually brought into a difeaied condition; as in lues originating from chancre, fmall-pox from inoculation, &c. 4. LTniverfo- AMERICAN EDITION. XXV 4. Univerfo-local; as if after a general ailment any particular part or organ is affedted in a fecondary way ; as the eruptions of exanthematous pyrexire, fyphilitic blotches, &c. And each of thefe forms of difeafes muff eonfift either in, 1 . Direct debility ; as in fcurvy, hunger, cold, &c. 2. Sthenic diathefis* as in pieurify, other forms of fynocha, &c. 3. Indirect debility ; as in old age, intoxication, fa- tigue, &c. 4. Diredt debility added to indirect ; as in gout very often, and in many difeafes of advanced life. 3. Indirect debility added to direct ; as in over-feed- ing a famifhed perion, &c. in molt difeafes of infants and young perfons. Let now the candid reader compare this view with the opinions of the old Methodists, and fay, whe- ther it be a mere revival of the practice of Them i son and Thessalus? Surely they who have afferted it was, can never be luppofed to have given themfelves the trouble to examine. Yet, with all this novelty about it, Brown’s doc- trine wants precifion. It proceeds not far enough be- yond general principles, which, by reafon of their ab- ftradt or fpeculative nature, have not been found clofely enough applicable to the fubjects of pathology and phyfiology — He takes for granted, for inftance, that the nervous fyftem is always one and the fame excitable thing. He fays fcarcely any . thing accurate on the different qualities of the blood and circulating fluids, and of the fecretions ; and gives nothing very minute concerning the mighty influence of the respiratory and digeftive proceffes upon the animal oeconomy. He palfes over entirely the chemical compoution of our food and drink, of our inhalations and excretions, of the gafes we breathe and the remedies we fwallow : in fhort, he has left not a fentence on the compofition or the na- c ture XXVI PREFACE TO THE ture of bone, mufcle, veffel, fat, lymph, or gluten,- nor how varioufly thefe are affeCted by difeafe, nor in what their healthy differs from their morbid ftate, nor by what means the alterations they undergo are brought about. Thefe, and other omiflions and defeats in the Bru- nonian System, called for amendment; and this was to be begun by attending to the varying condition of the living folid, and the concomitant ftate of the fluids. The eftabliftiment of the new nomenclature of chemiftry in France, in 1787, maybe confidered as forming a new epoch in fcience. Since the publica- tion of that invaluable performance, language has been adapted with greater accuracy to the expreflion of ideas, and philofophical inveftigation conducted with fuperior advantage and fuccefs. Lavoisier, in his Elements of Chemiftry, has attempted the ex- planation of the putrefactive, as well as the fermenta- tive procefs in the organized forms of animals and of plants, upon the modern principles; and, in a natural and convincing manner, has proceeded a great way beyond any one who undertook the explanation be • fore. Spallanzani indeed, in his Experiments on the ConcoCtion of Food in the Stomach, and Craw- ford, in his Application of the Principles of Com- buftion to the Function of the Lungs in breathing, v had given excellent fpecimens of this mode of reafon- ing on phyfiological lubjeCts. Great progrefs has been made fince in detecting the nature and properties of the atmofphere, the gales and seriform fluids ; and the right knowledge of thefe, derived from experiment and obfervation, has furnifhed the means of expound- ing many of the animal functions, in a plain and happy manner. W e do not merely know, as Prieftley and Scheele did, that there is a gafeous production, pure air, ne- ceffary to the prefervation and continuance of animal life ; AMERICAN EDITION. xxvii life ; but we think we know it is a compound fub- ftance, and what its compound ingredients are; we believe we can make and unmake it artificially, and that nature is doing fo inceifantly : we think the term “ dephlogifticated air” not accurately nor logically ap- plied; but, judging from its tendency to produce fournefs when combined with other bodies, we call the bafis of it “ the acidifying principle,” and the combination of that bafe with light and caloric, or the matter of heat, “ oxygene gas or air.” From noting the operation of this oxygene , or prin- ciple of fouring, upon various bodies, we imagine we know the compofition of acids, and have made out a .confiderable lift of acidifiable bafes ; fo that the format tion of fixed air from oxygene and carbone, or char- coal, of nitrous acid from it and azote, of vitriolic acid from the fame and fulphur, and phofphoric acid from its union with phofphorus, feem to be well efta- blilhed truths. We imagine that a certain other clafs of bodies capable of combining with oxygene, but not to the point of acidity, forms thereby half-acids or oxydes, and that thus the calces of metals, animal blood and fecretions, as well as the farinaceous, gum- my, and mucilaginous parts of plants, are formed. We think the compofition of water is underfliood, and inftead of being an elementary body, as was for- merly believed, that it is, in fadt, but the oxyde of hydrogen, or a combination of this latter fubftance with the principle of acidity, but not to the fouring point. It is confidered alfo, that more is known concern- ing the compofition of the irritable fibre, of the adi- pofe matter, and of the bones : and that the effects produced upon the circulated fluids by breathing, and through them upon the folids of the animal body in health, and the alterations too that the liquid and firm parts undergo by impeding, vitiating, or obftru cling that function, in ordinary cafes, as well as in gravid females* xxviii PREFACE TO THE females, are now better comprehended than they ufed to be. Jnafmuch, that, after the great light thrown upon this fubject by Goodwin, Girtanner has been enabled to drefs up the Brunonian Syftem in the more recent faihion, and Beddoes, to fupply and adcrn it with aimoft all that was wanting to make it additionally engaging and attractive. Subtncrlion, consumption, leurvy, ftone, catarrh, obefity, dropfy, and fever, have already received great elucidation, both in theory and practice, from the application of che- mical principles ; and we may reafonably hope, that before many more years elapfe, better and more cor- re<5t ideas will be entertained of many articles of the materia medica, and of their manner of operating; that a new medical nomenclature (than which nothing in fcience is more wanting) will be made out ; and that, from the ascertained condition of the body, and the known compoiition and operation of remedies, phyfi- cians may prefcribe fairly for the adtual ftate of the conftitution, and the removal of the prefent malady, without being milled, as too often happens at prefent, by fpecious words, and idle or deceitful names. But, notwithftanding the many and beautiful ap- plications of chemical principles to the explanation cf the animal functions, we are not to imagine every thing in life fufceptible of chemical interpretation. What it is that enables the atoms composing a mufcle to cohere, and the mufcle to contract and perform great exertions cf ftrength, we know not ; but this we know very well, that we can never form a mulcle by fyntheis, or the putting together, in any artificial form, thole fubftances which appear, from analyfis, to conftitute a mulcle. There is fomething in animated exiftence, which eludes our moft abtive relearches, and which defies fub million to either mechanical or chemical, lav/s. With r'dpect to chemical modes of reasoning upon thefe fubjedls, it is obfervable, that they apply, with their grcateft extent and accuracy, to AMERICAN EDITION. XXIX to fuch parts of the body as have the lowed: degrees of animation, as the teeth, bones, fat, and, generally fpeaking, the circulated and fecreted fluids ; while the qualities of mufcular fibres, by which they become contractile, and of nervous expanfions, whereby they take on fenfation, with the whole of the functions arifing fibm irritability and fenfibility, are referable to other and different laws. The inveftigation of thefe Laws of Organic Life is attempted by our learned and very ingenious author in the following work. The Zoonomia, therefore, though not exempt from fanciful and vifionary doc- trines, prefents confiderations of the firft importance, both to the fpeculative philofopher and the practical phyfician ; to him who contemplates the operations of mind as a fcience, or to him that attends to the cor- poreal functions as an artiffc. How far Dr. Darwin has fucceeded, and how much ftill remains to be done on this fubjedt, it may not perhaps be eafy to fay, efpe- cially fince his fecond volume has not yet reached us ; but I have no hefitation, from a confideration of the prefent work, to recommend it warmly to the perufal of ftudents, and efpecially of beginners, whofe unbi- afed minds will receive and comprehend its interefting contents, with lefs difficulty than thofe already occu- pied by pre-conceptions and prejudices. SAMUEL L. MITCHILL. Planclome , June 20 , 1 796 . , - . ■ ■ r * .. i • 1 t = , ' ■' T O ERASMUS DARWIN, ON HIS WORK ENTITLED Z 0 0 N 0 M I A, B } DEwHURST BILSBORROW. H.AIL to the Bard! who sung, from Chaos hurl’d How suns and planets form’d the whirling world ; How sphere on sphere Earth’s hidden strata bend, And caves of rock her central fires defend ; Where gems new-born their twinkling eyes unfold, £ And young ores shoot in arborescent gold. How the fair Fiower, by Zephyr woo’d, unfurls Its panting leaves, and waves its azure curls; Or spreads, in gay undress, its lucid form, To meet the sun, and shuts it to the storm; io While in green veins impassion’d eddies move. And Beauty kindles into life and love. How the first embryon-fibre, sphere, or cube, Lives in new forms, — a line, — a ring, — a tube; Closed in the womb with limbs unfinish’d laves, 1 5 Sips with rude mouth the salutary waves; Seeks round its cell the sanguine streams that pass. And drinks, with crimson gills, the vital gas; Weaves with soft threads the blue meandering vein, The heart’s red concave, and the silver brain; 20 Leads the long nerve, expands the impatient sense. And clothes in silken skin the nascent Ens. Erewhile, emerging from its liquid bed, It lifts in gelid air its nodding head; The light’s first dawn with trembling eye-lid hails, 25 With lungs untaught arrests the balmy gales; Tries its new tongue in tones unknown, and hears The strange vibrations with unpractised ears; Seeks with spread hands the bosom’s velvet orbs, With closing lips the milky fount absorbs; 30 And, xxxii TO ERASMUS DARWIN. And, as compress’d the dulcet streams distil. Drinks warmth and fragrance from the living rill ; Eyes with mute rapture every waving line, Prints with adoring kiss the Paphian shrine, And learns ere long the perfedf form confess’d, 3 j Ideal Beauty from its mother’s breast. Now in strong lines, with bolder tints design’d, You sketch ideas, and pourtray the mind; Teach how line atoms of impinging light To ceaseless change the visual sense excite; 40 While the bright lens collefts the rays, that swerve. And bends their focus on the moving nerve : How thoughts to thoughts are link’d with viewless chains, Tribes leading tribes, and trains pursuing trains; With shadowy trident how Volition guides, 45 Surge after surge, his intellectual tides; Or, Queen of Sleep, Imagination roves With frantic Sorrows, or delirious Loves. Go on, O Friend! explore with eagle-eye, Where wrapp’d in night retiring causes lie : 50 Trace their slight bands, their secret haunts betray. And give new wonders to the beam of day ; Till, link by link with step aspiring trod, You climb from Nature to the throne of God. So saw the Patriarch with admiring eyes 5 5 From earth to heaven a golden ladder rise ; Involved in clouds the mystic scale ascends, And brutes and angels crowd the distant ends. Trin. Col. Cambridge , Jan. 1, 1794. REFERENCES TO THE WORK. Botanic Garden , Part I. Line 1 3 Canto I. IV 1. 105. I.402. I. 1. 140. III. I.401. IV. I.452. I. 1. 14. Zoonoiuia. 12. Seel. XIII. ■13. XXXIX.4.1.- Line 18 26 3 ° 36 38 43 44 — ' 45 47 5 ° - 5 1 -54 Sett. XVI. 2. and XXXVIII -XVI. 4. XVI. 4. XVI. 6. III. and VII. X. XVIII. 17. XVII. 3. 7. XVIII. 8. XXXIX. 4. 8. XXXIX. the Motto. XXXIX. 8. PREFACE. The purport of the following pages is an endeavour to re- duce the fadts belonging to Animal Life into clafles, or- ders, genera, and fpecies ; and, by comparing them with each other, to unravel the theory of difeafes. It happened, perhaps unfortunately for the inquirers into the knowledge of difeafes, that other fciences had received improvement previous to their own ; whence, inftead of comparing the properties belonging to animated nature with each other, they, idly ingenious, bufied themfelves in attempting to explain the laws of life by thofe of mechanifm and chemiftry ; they confidered the body as an hy- draulic machine, and the fluids as pafling through a feries of chemical changes, forgetting that animation was its eflential charadteriftic. The great Creator of all things has infinitely diverfified the works of his hands, but has at the fame time damped a cer- tain iimilitude. on the features of nature, that demonftrates to us, that the whole is one family of one parent. On this limi- litude is founded all rational analogy ; which, fo long as it is concerned in comparing the eflential properties of bodies, leads us to many and important difcoveries ; but when with licentious activity it links together objects, otherwife difcordant, by fome fanciful fimilitude, it may indeed colledt ornaments for wit and poetry, but philofophy and truth recoil from its combinations. The want of a theory, deduced from fuch ftridt analogy, to condudl the pradtice ot medicine, is lamented by its profeflors - for, as a great number of unconnected facts are difficult to be acquired, and to be reafoned from, rhe art of medicine is in many inftances lefs efficacious under the diredtion of its wifeft pradtidoners ; and by that bufy crowd, who either boldly wade- in darknefs, or are led into endlefs error by the glare of falfe dieory, it is daily pradtifed to the deftrudtion of thoufands ; add to this the unceafing injury which accrues to the public by the perpetual advertifements of pretended noftrums ; the minds of the indolent become fuperftitioufly fearful of difeafes, which B they a PREFACE. they do not labour under ; and thus become the daily prey of fome crafty empyric. A theory founded upon nature, that fhould bind together the Scattered facts ot medical knowledge, and converge into one point ol view the laws ot organic life, would thus on many accounts contribute to the intereft of fociety. It would capa- citate men ot moderate abilities to pradtife the art of healing with real advantage to the public ; it would enable every one of literary acquirements to diftinguifh the genuine difciples of me- dicine from thofe of boafttul effrontery, or of wilv addrefs: and would teach mankind in fome important fituations the knowledge of therrtf elves. There are fome modem practitioners who declaim again ft medical theory in general, not confidering that to drink is to theorize ; and that no one can diredt a method o! cure to a per- fon labouring under difeafe without thinking, that is, without, theorizing ; and happy therefore is the patient, whole phyfician poffeffes the beft theoiy. The words idea, perception, fenfaricn, recollection, fug- geftion, and affoeiation, are each of them ufed in diis treatife in a more limited fenfe dian in the writers of metaphyfic. The author was in doubt, whedrer he fhould rather have lubftiruted new words inftead of diem; but was at lengdi of opinion, that new definitions ot words already in ufe would be lefs burthenfome to the memory of the reader. A great part of this work has lain by die writer above twenty years, as fome of his friends can teftify : he had hoped bv frequent revifion to have made it wordiy the acceptance of the public ; this however his odier perpetual occupations have in part prevented, and may continue to prevent, as long as he may be capable of revifmg it ; he therefore begs of die candid reader to accept of it in its prefent ftate, and to excufe any inaccuracies ol expreffion, or ol conclufion, into which die intricacy of his fubjeeft, the general imperfection of lan- guage, or the frailty he has in common with other men, ma\ have betrayed him ; and from which he has not die vanity to believe this treatife to be exempt. zoonomia: Z O O N O M I A SECT. I. OF MOTION. The whole of nature may be fuppofed to confift of twp effences or fubftances ; one of which may he termed fpirit, and the other matter. The former of thefe poflefTes the power to commence or produce motion, and die latter to receive and communicate it. So that motion, ccnfidered as a caufe, imme- diately precedes every effedd and, confidered as an effect, it immediately fucceeds every caufe. The motions of matter may bedivided into two kinds, primary and fecondary. The fecondary motions are thofe which are given to or received from other matter in motion. Their laws have been iuccefsfully inveftigated by philofophers in dieir treatifes on mechanic powers. Thefe motions are dif- tinguifhed by this circumftance, that the velocity multiplied into the quantity of matter of the body added upon, is equal to the velocity multiplied into the quantity of matter of the adding body. The primary motions of matter may be divided into diree claffes, thofe belonging to gravitation, to chemiftry, and to life ; and each clafs has its peculiar laws. Though thefe three dalles include the motions of folid, liquid, and aerial bodies ; there is neverthelefs a fourth divilion of motions ; I mean thofe of the fuppofed ethereal fluids of magnet! fm, eleddricity, heat, and light ; whofe properties are not fo well inveftigated as to be clafled with fufficient accuracy. i ft. The gravitating motions include the annual and diurnal rotation of the earth and planets, the flux and reflux of the ocean, the defeent of heavy bodies, and other phenomena of gravitation. The unparalleled fa gacity of the great Newton has deduced the laws of this clafs of motions from the Ample prnciple of the general attraddion of matter. Thefe motions are diftinguifhed by their tendency to cr from the centers of the fun or planets. 2 d. The chemical clafs of motions includes all the various appearances of chemiftn . Many of the fadds, which belong 4 DEFINITIONS. Sect. II. i. to thefe branches of fcience, are nicely afcertained, and ele- gantly claffed ; but their laws have not yet been developed from Inch fimple principles as dime above-mentioned; though it is probable, that they depend on the fpecihc attractions belong- ing to the particles of bodies, or to the difference of the quan- tity of attradlion belonging to the tides and angles of thofe par- ticles. The chemical motions are diftinguifhed by their being generally attended with an evident decompolition or new com- bination of the a (Stive materials. The third clafs includes all the motions of the animal and vegetable world ; as well thofe of the veffels, which cir- culate their juices, and of the mufcles, which perform uieir locomotion, as thofe of the organs of fenfe, which conftitutc their ideas. This laid: clafs of motion is the fubject of the following pages, which, though confcious of their many imperfections, I hope may give fome pleafure to the patient reader, and contri- bute fomething to the knowledge and to the cure of difeafes. ' SECT. II. i. EXPLANATIONS AND DEFINITIONS. I. Outline of the animal economy . — II. I. Of the fenfenum. 2. Of the brain, and nervous medulla. 3. A nerve. 4. A mufcular fibre. 5. The immediate organs of fenfe. 6. The external organs of Jenfe. 7. An idea or fenfual motion. 8. Perception. 9. Scnfation. 10. Rccollcftion and Jug- gejiion. 11. Habit, caujation, afifociation, catenation. 12. Ref ex ideas. 13: Stimulus defined. As fome explanations and definitions will be necefTary in the profccutlon of the work, the reader is troubled with them in this place, and is intreated to keep them in his mind as he proceeds, and to take them for granted, till an apt opportunity occurs to evince their truth ; to which I lhall premife a very fliort outline of the animal economy. I. — I. THE nervous fyftem has its origin from tire brain, and is diftributed to every part of die body. Thofe nerves, which ferve the fenfes, principally arife from that part of the bram, which is lodged in the head ; and thofe, which ferve the purpofes of mufcular motion, principally arife from diat part «?f Sect.II. i. DEFINITIONS. 5 of the brain, which is lodged in tire neck and back, and which is erroneoufly called the fpinal marrow. The ultimate fibrils of thefe nerves terminate in the immediate organs of fenfe and mufcular fibres, and if a ligature be put on any part of their pafifage from the head or fpine, all motion and perception ceafe in the parts beneath the ligature. 2 . The longitudinal mufcular fibres compofe the locomotive mufcles, whofe contradfions move the bones of the limbs and trunk, to which tlieir extremities are attached. The annular or fpiral mufcular fibres compofe the vafcular mufcles, which conftitute the inteftinal canal, the arteries, veins, glands, and abferbent veffels. 3. The immediate organs of fenfe, as the retina of the eye, probably confift of moving fibrils, with a power of contra chon limilar to that of the larger mufcles above deferibed. 4. The cellular membrane conlifts of cells, which refemble thofe of a fponge, communicating with each other, and ccn- nedting together all die other parts of the body. 5. The arterial fyftem conlifts of the aortal and die pulmo- nary artery, which are attended through their wlioie courfe with their correfpondent veins. The pulmonary a r eery re- ceives die blood from the right chamber of the heart, and car- ries it to the minute extenlive ramifications of the lungs, where it is expofed to the action of the air on a furface equal to that of the whole external Ikin, through the thin moift coats of thofe veffels, which are fpread on the air-cells, which conftitute die minute terminal ramifications of die wind-pipe. Here die blood changes its colour from a dark red to a bright fcarlet. It is then collected by the branches cf tire pulmonary vein, and conveyed to the left chamber of the heart. 6. The aorta is another large artery, which receives the blood from the left chamber of the heart, after it has been thus aerated in the lungs, and conveys it by afeending and descending branches to every other part of the fyftem : the extremities of this artery terminate either in glands, as the falivary glands, la- chrymal glands, &c. or in capillary veflels, which are probably lefs involuted glands ; in thefe fome fluid, as faliva, tears, per- fpiration, are feparated from the blood ; and the remainder of the blood is abforbed or drank up by branches of viens correfpon- dent to the branches of the artery ; which are fumifhed with valves to prevent its return; and is thus carried back, after having again changed its colour to a dark red, to the right chamber of the heart. The circulation of the bleed in the liver differs from this general fyftem ; for the veins which drink up the refluent blood from thofe arteries, which arc fpread on the ' . . bowels <3 DEFINITIONS. Sect. II. 2. bowels and mefentery, unite into a trunk in the liver, and fern; a kind of artery, which is branched into the whole fubftance of the liver, and is called the vena portarum; and from which the bile is feparated by die numerous hepatic glands, which conftitute that vifeus. 7. The glands may be divided into three fy items, die con- voluted glands, fuch as tliofe above deferibed, which feparare bile, tears, faliva, See. Secondly, the glands without convo- lution, as the capillary vellels, which unite the terminations of the arteries and veins, and feparate both the mucus, which lubricates the cellular membrane, and the peripirable mart': which preferves the (kin moift and flexible, A. id diirdly, the whole abforbent fyftem, confiding of the la&eals, which open their mouths in the ftomach and inteftines, and of the lym- phatics, which open their mouths on the external iurface of the body, and on the internal linings of the ceils of the cellular membrane, and other cavities of the body. Thefe lacteal and lymphatic veil'd s are furniflied tilth nu- merous valves to prevent the return of the fluids, which they abforb, and terminate in glands, called lymphatic glands, and may hence be ccnftdered as long necks or mouths belonging to thefe glands. To thefe they convey the chyle and mucus, with a part of the perfpirable matter, and atmofpheric nioifture : all which, after having puffed through tliefe glands, and having fuffered fome change in them, are carried forward into the blood, and fupply perpetual ncurifhment to the fyftem, or re- place its hourly wade. 8. The ftomach and inteftinal canal have a conftant vermi- cular motion, which carries forward their contents, after the ladleals have drank up the chyle from them; and which is ex- cited into adbion by the ftimulus of the aliment we fwallow, but which becomes oceaftonally inverted or retrograde, as in vomit- ing, and in the iliac paflion. 11 . 1. The word jcnforium in the following pages is deflgned to exnrefs not only the medullary part of the brain, fpinal mar r row, nerves, organs of fenfe, and of die mufcles; but alfo at the fame time that living principle, or fpirit ofanimation, which relides throughout the body, without being cognizable to our fenfes, except by its exFefts. The changes which oceaftonally take place in the fenforium, as during die exertions of volition, or the fenfations of pleafure or pain, are termed fenforial na- tions. 2. Thefimilarity of the texture of the brain to diat of the pancreas, and fome other glands of the bodv, has induced the inquirers into this fubjedl to believe, that a fluid, perhaps muc.i more DEFINITIONS. Sect. II. 2. more fubtile than the eteCtric aura, is feparated from the blood by that organ for the purpofes of motion and fenfation. When we recolleCt, that the eleCtric fluid itfelf is actually accumu- lated and given out voluntarily by the torpedo and tire gyrnno- tus eledtricus, drat an eledfric fhock will frequently ftinrulate into motion a paralytic limb, and laftly, that it needs no per- ceptible tubes to convey it, this opinion feems not without pro- bability; and the lingular figure of the brain and nervous fyf- tem feems well adapted to diftribute it over every part of the the medullary fubfcance of the brain not only occupies the cavities of the head and fpine, but pafles along the innu- merable ramifications of the nerves to the various mufcies and organs of fenfe. In thefe it lays afide its coverings, and is in- termixed with the Fender fibres, which ccnftitute drofe mufcies and organs of fenfe. Thus all thefe diftairt ramifications of tire fenforium are united at one of their extremities, that is, in the head and fpine ; and thus thefe central parts of the cenfoii- um conftitute a communication between all the organs of feme and mufcies. 3. A nerve is a continuation of the medullary fubftance of dre brain from the head or fpine towards the other parts of the body, wrapped in its proper membrane. 4. The mufcular fibres are moving organs intermixed 'yvith drat medullary fubftance which is continued along the nerves, as mentioned above. They are indued with the power of con- traction, and are again elongated eidrer by antagonift mufcies, by circulating fluids, or by elaftic ligaments. So dre mufcies on the one fide of the fore-arm bend the fingers by means of their tendons, and thofe on the other fide of the fore-arm ex- tend them again. The arteries are diftended by the circulating blood; and in the necks of quadrupeds there is a ftrong elaftic ligament, which afiifts the mufcies, which elevate the head, to keep it in its horizontal pofition, and to raife it after it has been deprefied. 5. The immediate organs of fenfe confifc in like manner of moving fibres enveloped in the medullary fubftance above men- tioned; and are erroneoufly fuppofed to be fimply an ex cm, li- on of the nervous medulla, as dre retina of the eye, and dre rete mucofunr of the {kin, which are the immediate organs of vifion, and of touch. Hence, when we fpeak of the contrac- tions of the fibrous parts of the body, we fhall mean both die contractions of the mufcies, and thofe of the immediate organs of fenfe. Tlrefe fibrous motions are thus diftinguiflred from the fieri forial motions above mentioned. 6. The 8 DEFINITIONS. Sect. II. 2, 6. The external organs of fenfe are the coverings of the immediate organs of fenfe, and are mechanically adapted for the* reception or tranfmiffion of peculiar bodies, or of their qualities, as the cornea and humours of the eye, the tympanum of the ear, the cuticle of the fingers and tongue. 7. I he word idea has various meanings in the writers of metaphyfic : it is here uled limply for thofe notions of external things, which our organs of fenfe bring us acquainted with originally; and is denned a contraction, or motion, or con- figuration, oi the fibres, which conftitute die immediate or- gan of fenfe ; which will be explained at large in anodier part of the work. Synonymous with the word idea, we (hall iome- times ufe the words fenfual motion, in contradiftindtion to muf- cular motion. 8. The word perception includes both the adtion of the or- gan of fenfe in confequence of die impadt of external objects, and our attention to that adtion ; that is, it expreffes both die motion of the organ of fenfe, or idea, and the pain or pleafure that iucceeds or accompanies it. 9. The pleafure or pain which neceffarily accompanies all thofe perceptions or ideas which we attend to, either gradually iubiides, or is fucceeded by other fibrous motions. In the lat- ter cafe it is termed fenfation, as explained in Sedt. V. 2, and AT.- 2. — The reader is intreated to keep diis in his mind, that through all this treatife die word fenfation is ufed to exprels pleafure or pain only in its adtive Hate, by whatever means it is introduced into die fyftem, without any reference to the fli- mulation of external objects. 10. The vulgar ufe of the word memory is too unlimited for our purpofe : thole ideas which we voluntarily recall are here termed ideas of recolledhon, as when we will to repeat the alphabet backwards. And thofe ideas which are fuggefted to us by preceding ideas, are here termed ideas of fuggeftion, as whilfl: we repeat die alphabet in the ufual order; when by- habits previoully acquired B is fuggefted by A, and C by B, without any effort of deliberation. 1 1. The word affociation properly fignifies a fociety or con- vention of things in fome reipedts iimilar to each odier. We never fay in common language, that the effect is affociatcd with the caufe, though they nteeffariiy accompany or lucceed each other. Thus die contractions or our mufcles and organs of fenfe may be laid to be affociated with irritations, or with volition, or with fenfation ; becaufe they are caufed bv them, as mentioned in Sedt. IV. When fibrous contradtions fuc- cced other fibrous contradtions, the conacdtion is termed affo- Sect. III. MOTIONS OF THE RETINA. 9 elation ; when fibrous contractions fucceed fenforial motions, the connection is termed caufation ; when fibrous and fenforial motions reciprocally introduce each other in progreffive trains or tribes, it is termed catenation of animal motions. All thefe connections are faid to be produced by habit ; that is, by fre- quent repetition. 12. It may be proper to obferve, that by the unavoidable idiom of our language the ideas of perception, of recolleCtion, or of imagination, in the plural number fignify the ideas be- longing to perception, to recolleCtion, or to imagination; whiilt the idea of perception, of recolleCtion, or of imagina- tion, in the lingular number is ufed for what is termed “ a re- flex idea of any of thofe operations of the fenforium.” 13. By the word Jlimulus is not only meant the application of external bodies to our organs of lenfe and mufcular fibres, which excites into aCtion the fenforial power termed irritation ; but alio pleafure or pain, when they excite into aCtion the fen- forial power termed lenfation; and defire or averflon, when they excite into aCtion the power of volition ; and laftly, the fibrous contractions which precede affociation; as is further explained in SeCt. XII. 2. 1. SECT. III. THE MOTIONS OF THE RETINA -DEMONSTRATED BY EXPERIMENTS. I. Of animal motions and of ideas. II. The fibrous Jlrudiure of the retina. III. The adiivlty of the retina in vifion. 1. Rays of light have no momentum. 2. Objects long viewed become fainter . 3. Spedira of black objects become lumi- nous. 4. Varying fpe dir a from gyration. 5. From long in - fpedtion of various colours. IV. Motions of the organs of fenfe confiitute ideas. 1. Light from prejfing the eye- ball , and jound from the pulfation of the caroted artery. 2 . Ideas in fieep miftaken for perceptions. 3. Ideas of ima- gination produce pain and ficknefs like fenfations. 4. IVhen the organ of fenje is defrayed , the ideas belonging to that Jenfe perijh. V. Analogy between mufcular motions and fenjual motions, or ideas. 1. They are both originally excited by irritations. 2. And affociatcd together in the fame manner. 3. Both adi in nearly the fame times. 4. Are alike firengthened or fatigued by exerclfe. 5. Are alike painful from inflammation. 6. Are alike benumbed by com - C prejfon . xo MOTIONS OF THE RETINA. Sect. III. i, preffon. 7. Are alike liable to paralyjis. 8. To convulfion . 9. To the influence of old age. VI. Objections anfwered. X. Why we cannot invent new ideas. 2. If ideas referable external'objeCts. 3. Of the imagined fenfation in an am- putated limb. 4. AbfiraCt ideas. VII. What are ideas , if they are not animal motions. BEFORE the great variety of animal motions can be duly arranged into natural claffes and orders, it is neceffary to fmooth the way to this yet unconquered field of fcience, by removing fome obftacles which thwart our paffage. I. To demonflratc that the retina and other immediate organs of fenfe poffefs a power of motion, and that thefe motions conftitute our ideas, according to the fifth and feventh of the preceding affertions, claims our firfl attention. Animal motions are diftinguifhed from the communicated motions, mentioned in the firft fedlion, as they have no mecha- nical proportion to their caufe ; for the goad of a fpur on the fkin of a horfe fhall induce him to move a load of hay. They differ from the gravitating motions there mentioned, as they are exerted with equal facility in all directions ; and they differ from the chemical clafs of motions, becaufe no apparent de- compofitions or new combinations are produced in the moving materials. Hence, when we fay animal motion is excited by irritation, we do not mean that the motion bears any proportion to the mechanical impulfe of the flimulus ; nor that it is affedled by the general gravitation of the two bodies ; nor by their chemical properties ; hut foiely, that certain animal fibres are excited into adlion by fomething external to the moving organ. In this fenfe the flimulus of the blood produces the contrac- tions of the heart ; and the fubflances we take into our ftomach and bowels irritate them to perform their neceffarv functions. The rays of light excite the retina into animal motion by their flimulus ; at the fame time that thofe rays of light themfelves are phyfically converged to a focus by the inactive humours of the eve. Tire vibrations of the air irritate the auditory nerve into animal adlion; while it is probable that the tympanum of the ear at the fame time undergoes a mechanical vibration. To render this tire um fiance more eafy to be comprehended. motion may be defined to be a variation cf figure ; for the whole univerfe may be confidered as one thing poffeffing a cer- tain figure; the motions of any of its parts are a variation of this figure of the whole : this definition of motion will he fur- ther explained in Sect. XiV. 2. 2. on the production of ideas. Now, £ . <■ . - ' : ' i.'- V : *• . V II Sect. III. i. MOTIONS OF THE RETINA. Now, the motions of an organ of fenfe are a fucceflion of configurations of that organ ; thefe configurations fucceed each other quicker or flower ; and whatever configuration of this organ of fenfe, that is, whatever portion of the motion of it is, or has ufuallv been, attended to, conftitutes an idea. Hence the configuration is not to be confidered as an effect of the mo- tion of the organ, but rather as a part or temporary termination of it; and that, whether a paufe fucceeds it, or a new configu- ration immediately takes place. . Thus, when a fucceflion of moving objects are prefented to our view, the ideas of trumpets, horns, lords and ladies, trains and canopies, are configurations, that is, parts or links of the fucceflive motions of the organ of vifion. Thefe motions, or configurations of the organs of fenfe, differ from the fenforial motions to be defcribed hereafter, as they appear to be Amply contractions of the flbrous extremi- ties of thofe organs, and in that refpect exactly referable the motions or contractions of the larger mufcles, as appears from the following experiment :■ — Place a circular piece of red Aik, about an inch in diameter, on a flieet of white paper, in a Arong light, as in Plate I.- — look for a minute on thi^area, or till the eye becomes fomewnat fatigued, and then, gently cloAng your eyes, and {hading them with your hand, a circular green area of die fame apparent diameter becomes viAble in the clofed eye. This green area is the colour reverie to the red area, which had been previoufly infpected, as explained in experiments on ocu- lar fpectra at the end of the work, and in Botanical Garden, P. I. additional note, No. I. Hence it appears, that a part of me retina, which had been fatigued by contraction in one di- rection, relieves itfelf by exerting the antagonifl: Abres, and pro- ducing a contraction in an oppoAte direction, as is common in the exertions of our mufcles. .Thus, when we are tired with long action of our arms in one direction, as in holding a bridle on a journey, we occaAonally throw them into an oppoAte poAtion to relieve the fatigued mufcles. Mr. Locke has dehned an idea to be “ whatever is prefent to the mind;” but this would include the exertions of volition, and the fenfations of pleafure and pain, as well as thofe opera- tions of our fyAem, which acquaint us with external objects ; and is therefore too unlimited for our purpofe. Mr. Locke feems to have fallen into a further error, by conceiving that the mind could form a general or abftract idea by its own operation, which was the copy of no particular perception ; as of a triangle in general, that was neither acute, obtufe, nor right angled. The ingenious Dr. Berkley and Mr. Hume have demonftrated, that 12 MOTIONS OF THE RETINA. Sect. III. 2. 3. that fuch general ideas have no exiftence in nature, not even In the mind of their celebrated inventor. We fhall therefore take for granted at prefent, that our recollection or imagination of external objects conlifts of a partial repetition of the percep- tions which were excited by thofe external objects at the time we became acquainted with them; and that our reflex ideas of the operations of our minds are partial repetitions of thofe operations. II. The following article evinces that the organ of vifion confifts of a fibrous part as w 7 ell as of the nervous medulla, like other white mufcles ; and hence, as it refembles the mufeu- lar parts of the body in its ftruclure, we may conclude, that it muft refemble them in pofTefling a power of being excited into animal motion. — The fubfequent experiments on the optic nerve, and on the colours remaining in the eye, are copied from a paper on ocular fpedxa, publifhed in the 76th volume of the Philof. Tranf. by Dr. R. Darwin of Shrewfbury, which, as I ihall have frequent occafion to refer to, is reprinted in this work, Seci. XL. The retina of an ox’s eye was fufpended in a glafs of warm water, and forcibly torn in a few places ; the edges of drefe pa/ts appeared jagged and hairy, and did not con- tract and become fmooth like Ample mucus, when it is diftended till it breaks, which evinced that it conlifted of fibres. This fibrous conftru&ion became ftill more diftinCt to the light by adding fome cauftic alkali to the water; as the adhering mucus was firft eroded, and the hair-like fibres remained floating in theveflel. Nor does the degree of tranfparency of the retina Invalidate this evidence of its fibrous ftruCture, fince Leeuwen- hoek has fhewn, that the chryftaline humour itfelf confifts of fibres. Arc. Nat. V. I. 70. Hence it appears, that as the mufcles confift of larger fibres, Intermixed with a fmaller quantity of nervous medulla, the organ of vifion conlifts of a greater quantity of nervous medul- la, intermixed with fmaller fibres. It is probable that the loco- motive mufcles of microfcopic animals may have greater tenuity than thofe of the retina ; and there is reafon to conclude, from analogy, that the other immediate organs of fenfe, as the portio mollis of the auditory merve, and the rete mucofum of the fkin, poflefs a iimilarity of ftruCture with the retina, and a fimilar power of being excited into animal motion. III. The fubfequent articles fhew, that neither mechanical impreiiions, nor chemical combinations of light, but that the animal activity of the retina conftitutes vifion. 1. Much has been conjectured, by philofophers, about the momentum of the rays of light: to fubjeCt this to experiment, a verv . . < ’ ■ ' < Sect. III. 3. MOTIONS OF THE RETINA. 13 a very light horizontal balance was conftructed by Mr. Michel, with "about an inch fquare of thin leaf-copper fufpended at each end of it, as defcribed in Dr. Pfieftley’s Hiftory of Light and Colours. The focus of a very large convex mirror was thrown by Dr. Powel, in his leisures on experimental philofophy, in my prefence, on one wing of this delicate balance, and it re- ceded from the light; thrown on the other wing, it approached towards the, light, and this repeatedly; fo that no fenfible im- pulfe could be obferved, but what might well be afcribed to the afcent of heated air. Whence it is reafonable to conclude, that the light of the day muft be much too weak, in its dilute Hate, to make any mechanical imprefiion on fo tenacious a fubftance as the retina of the eye. — Add to this, that as the retina is nearly tranfpa- rent, It could therefore make lefs refiftance to the mechanical impulfe of light ; which, according to the obfervations related by Mr. Melvil, in the Edinburgh Literary Eflays, only com- municates heat, and fhould therefore only communicate mo- mentum, where it is obftrudled, refle&ed, or refratfled. — ■ From whence alfo may be collected the final caufe of this de- gree of tranfparency of the retina, viz. leaft by the focus of flronger lights, heat and pain fhould have been produced in the retina, inftead of that ftimulus which excites it into ani- mal motion. 2. On looking long On an area of fcarlet filk of about an inch in diameter laid on white paper, as in Plate I. the fcarlet Colour becomes fainter, till at length it entirely vanifhes„ though the eye is kept uniformly and fteadily upon it. Now, if the change or motion of the retina Was a mechanical im- preffion, or a chemical tinge of coloured light, the perception would every minute become flronger and flronger, — -whereas ih this experiment it becomes every inftant weaker and weaker. The fame circumftance obtains in the continued application of found, or of fapid bodies, or of odorous ones, or of tangi- ble ones, to their adapted organs of fenfe. Thus, when a circular coin, as a {hilling, is prefled on the palm of the hand, the fenfe of touch is mechanically com- prefled ; but it is the flimulus of this preflure that excites the organ of touch into animal adbion, which conftkutes the per- ception of hardnefs and of figure: for in fome minutes the perception ceafes, though the mechanical preflure of the ob- ject remains. 3. Make with ink on white paper a very black fpot about half an inch in diameter, with a tail about an inch in length, io as to refemble a tadpole, as in Plate II.; lcck ftecflaftly D for i 4 MOTIONS OF THE RETINA. Sect. III. 3. for a minute on the center of this fpot, and on moving the eve a little, the figure of the tadpole will be feen on the white part of the paper ; which figure of the tadpole will appear more luminous than the other part of the white paper; which can only be explained by fuppofing that part of the retina, on, which the tadpole was delineated, to have become more fenfible to light than the other parts of it, which were expof- ed to the white paper; and not from anv idea of mechanical imprefhon or chemical combination of light with the retina. 4. When any one turns round rapidly, till he becomes diz- zy, and falls upon the ground, the lpedra of the ambient ob- jedls continue to prefent themfelves in rotation, and he feeins to behold the objects ftill in motion. Now if thefe fpedtra were impreiTions on a paftive organ, they either muft conti- nue as they were received laft, or not continue at all. 5. Place a piece of red filk, about an inch in diameter, on a Iheet of white paper, in a ftrong light, as in Hate I. ; look ftea- dily upon it, from the diftance of about half a yard, for a minute ; then doling your eye-lids, cover them with your hands and handkerchief, and a green fpedtrum will be feen in your eves, relembling, in form, the piece of red lilk. After fome feconds of time the fpectrum will difappear, and in a few more feconds will re-appear ; and thus alternately three or fcJur times, if the experiment be well made, till at length it vanishes entirely. 6. Place a circular piece of white paper, about four inches in diameter, in the funfhine ; cover the center of this with a circular piece of black iilk, about three inches in diameter ; and the center of the black lilk with a circle of pink filk, about two inches in diameter; and the center of the pink filk with a circle of yellow lilk, about one inch in diameter; and the center of this with a circle of blue filk, about half an inch in diameter ; make a linall fpot with ink in the center of the blue lilk, as in Plate III. ; look fteadily for a minute on this central fpot, and then doling your eyes, and applying your hand at about an inch diflance before them, fo as to prevent too much or too little light from palling through the eve-lids, and you will fee the mold beautiful circles ot colours that imagina- tion can conceive ; \Vhich are moll refembled by the colours occalioned by pouring a drop or two of oil on a ftill take in a bright day. But thefe circular irifes of colours are not only different from the colours of the filks above-mentioned, but are at the fame time perpetually changing as long as they exift. From all thefe experiments it appears, that thefe fpedra in the eye are not owing to the mechanical impulfe of light im- prelTcd. * •1 * * % \ Sect. ill. 4- MOTIONS OF THE RETINA. 15 preffed on the retina ; nor to its chemical combination with that organ ; nor to the abforption and emiflion of light, as is fuppofed, perhaps erroneoufly, to take place in calcined {hells and other phofphorefcent bodies, after having been expofed to the light : for in all thefe cafes the lpeclra in the eye {honld ei- ther remain of the fame colour, or gradually decay, when the object is withdraw ; and neither their evanefcence during the prefence of their objedl, as in the fecond experiment, nor their change from dark to luminous, as in the third experiment, nor their rotation, as in the fourth experiment, nor the alternate prefence and evanefcence of them, as in the fifth experiment, nor the perpetual change of colours of them, as in the lafl experiment, pould exifl. IV. The fubfequent articles fhew, that thefe animal motions, or configurations of our organs of fenfe, conftitute our ideas. 1 . If any one in the dark preffes the ball of his eye, by ap- plying his finger to the external corner of it, a luminous ap- pearance is obferved ; and by a fmall flroke on the eye great flafhes of fire are perceived. (Newton’s Optics.) So that, when the arteries, that are near the auditory nerve, make ftronger pulfations than ufual, as in fome fevers, an undulating found is excited in the ears. Hence it is not the prefence of the light and found, but the motions of the organ, that are immediately neceffary to conftitute the perception or idea of light and found. 2. During the time of deep, or in delirium, the ideas of imagination are miftaken for the perceptions of external ob- jects ; whence it appears, that thefe ideas of imagination are no other than a reiteration of thofe motions of the organs of fenfe, which were originally excited by th<= ftimulus of external ob- jedfs : and in our waking hours the fimple ideas, that we call up by recolledfion or by imagination, as the colour of red, or the fmell of a rofe, are exadf refemblances of the fame fimple ideas from perception ; and in confequence mu ft be a repetition of thofe very motions. 3. The difagreeable fenfation called the tooth-edge is origi- nally excited by the painful jarring of the teeth in biting the edge of the glafs, or porcelain cup, in which our food was given us in our infancy, as is further explained in the Section XVI. 10, on Inftindt. — This difagreeable fenfation is after- wards excitable not only by a repetition of the found, that was then produced, but by imagination alone, as I have my- felf frequently experienced ; in this cafe the idea of biting a china cup, when 1 imagine it very diftindfly, or when I fee another perfon bite a cup or glafs, excites, an aclual pain in the *6 '"MOTIONS OF THE RETINA. Sect. Ill 4 , the nerves of mv teeh. So that this idea and pain feem to be -nothing more than the reiterated motions of thofe nerves, that were formerly fo difagreeably affected . Other ideas that are excited by imagination or recollection in many infiances produce firailar effects on the conftitution, as our perceptions had formerly produced, and are therefore undoubtedly a repetition of the fame motions. A fforv which the celebrated Baron Van Swietop relates of himfelf is to this purpofe. He was prefent when the putrid carcafe of a dead dog exploded with prodigious Bench; and fo me rears after- wards, accidentally riding along the fame road, he was thrown mto tire fame ficknefs and vomiting by the idea of tips Bench, as he had before experienced from the perception of it. 4. Vv r here the organ of fenfe is totally dcBroved, the ideas which were received by that organ feem to perilh along with it, as wejl as the power of perception. Of this a fatisfackorv mftance has fallen under my .obfervation. A gentleman about fixty years of age had been totally deaf for near thirty years ; he appeared to be a man of good underllanding, and amufed himfelf with reading, and by converfing either bv the ufe of the pen, or by figns rpide with his fingers, to reprefent letters. I obferved that he had fo far forgot the pronunciation of the language, that when he attempted to fpeak, none of his words had difiindk articulation, though his relations could fometimes underhand his meaning. But, which is much to the point, he allured me, that in his dreams he always imagined that peo- ple converfed with him by figns or writing, and never that Ire heard any one fpeak to him. From hence it appears, that with the perceptions of founds Ire Iris alio lofi the ideas of them ; though the organs of fpeech Bill retain fopnewhat of their ufual habits of articulation. This obfervation may throw fome light on the medical treat- ment of deaf people ; as it may be learnt from their dreams whether tire auditory nerve be paralytic, or their deafnefs be owing to fome defebi of the external organ. Jt rarely happens that the immediate organ of vifion is per- fectly deffroved. The mofi frequent caufes of blindnefs are occafioned by defects of the external organ, as in cata rafts and obfufeations of the cornea. But I have had the opportu- nity of converfing with two men, who had been fome years blind ; one of them had a complete gutta ferena, and tire other had lofi the ivhole fubfiance of his eyes. They both told me that they did not remember to have ever dreamt of vilible ob- jects, fince the total lofs of their fight. V, Another method of difeovering that our ideas are ani- mal Sect. III. 5. MOTIONS OF THE RETINA. 17 mal motions of the organs of fenfe, is from conlidering the great analogy they bear to the motions of the larger mufcles of the body. In the following articles it will appear that they arc originally' excited into adtion by the irritation of external objects like our mufcles ; are afibciated together like curmuf- cular motions ; act in fnnilar time with them ; are' fatigued by continual exertion like them; and that the organs of fenfe are fubject to inflammation, numbnefs-, palley, convulfron, and the defedts of old age, in the fame manner as the mufcular fibres. 1. All our perceptions or ideas of external objects are uni- verfally allowed to have been originally excited by the ftimu- lus of thole external objedts ; and it will be fhewn in a luc- ceeding fedtion, that it is probable that all our mnfeular mo- tions, as well thole that are become voluntary as thole of the heart and glandular lyitem, were originally in like manner excited by the ftimulus of fomething external to the organ of motion. 2. Our ideas are alfo affociated together after their produc- tion precifely in the lame manner as our mulcular motions , which will likewife be fully explained in the lucceeding fecaon. 3. The time taken up in performing an idea is likewife much the fame as that taken up in performing a mufcular mo- tion. A mufician can prefs the keys of an harplichord with his fingers in the order of a tune he has been aceuftomed to play, in as little time as he can run over' thole notes in his mind. So we many times in an hour cover cur eye-balls with our eye-lids without perceiving that we are in the dark ; hence the perception or idea of light is not changed for that of daik- nels in fa fmall a time as the twinkling of an eye ; fo that in. this cafe the mufcular motion of the eye-lid is performed quicker than the perception of light can be changed for that of darknefs. — So if a rire-ilick be whirled’ round in the dark, a luminous circle appears to the obferver; if it be whirled iomewhat flower, this circle becomes interrupted in one part and then the time taken -up in fucha revolution of the flick is the lame that the obferver ufes in changing his ideas : thus the. oxo- of Homer, the long ihadow of the flying ja- velin, is elegantly defigned to give us an idea of its velocity, and nor of its length. 4. I he fatigue that follows a continued, attention of the mind to-one object is relieved by changing the iubjedt of our thoughts ; as the continued movement of one limb is relieved by moving another in its head. Whereas a due exercife -of *he faculties cf the mind llrengtfwns and improves thole facul- ties. 18 MOTIONS OF THE RETINA. Sect. III. 5 ; ties, whether of imagination or recollection ; as the exercife of our limbs in dancing or fencing increafes the ftrength and agility of life mufcles thus employed. 5. If the mufcles of any limb are inflamed, they do not move without pain ; fo when the retina is inflamed, its mo- tions alfo are painful. Hence light is as intolerable in this kind of ophthalmia, as the preffure is to the Anger in the pa- ronychia. In this difeafe the patients frequently dream of having their eyes painfully dazzled ; hence the idea of ftrong light is painful as well as the reality. The firfl of thefe facts evinces that our perceptions are motions of the organs of fenfe ; and the latter, that our imaginations are alfo motions of the fame organs. 6. The organs of fenfe, like the moving mufcles, are lia- ble to become benumbed, or lefs fenfible, from compreffion. Thus, if any perfort on a light day looks on a white wall, he may perceive the ramifications of the optic artery, at every Sulfation of it, reprefented by darker branches on the white wall ; which is evidently owing to its comprefling the retinue during the diaftole of the artery. Savage Nofolog, 7. The organs of fenfe and the moving mufcles are alike liable to be afFedted with paify, as in the gutta ferena, and in fome cafes of deafnefs ; and one fide of the face has fometimes loft its power of fenfation, but retained its power of motion ; other parts of the body have loft their motions, but retained their fenfation, as in the common hemiplagia ; and in other inftances both thefe powers have perifhed together. 8. In fome convulfive difeafes a delirium or infanity fuper- venes, and theconvulftons ceafe ; and converfelv the convul- flons {hall fup'ervene, and the delirium ceafe. — Of this I have been a witnefs many times in a day in the paroxyfms of violent epilepftes ; which evinces that one kind of delirium is a convul- fion of the organs of fenfe, and that our ideas are the motions of thefe organs : the fubfequent caies will illuftrate this ob- fervation. Mils G , a fair young lady, with light eyes and hair, was ieized with moft violent convuliions of her limbs, with outrageous hiccough, and moft vehement efforts to vomit : af- ter near an hour was elapfed this tragedy ceaied, and a calm talkative delirium fupervened for about another hour ; and thefe relieved each other at intervals during the gieateft part of three or four days. After having carefully coiiftdered this difeafe, I thought the convuliions of her ideas lefs dangerous than thofe of her mufcles , and having in vain attempted to make any opiate continue in her ftbmaeh, an ounce of lauda- num Sect. III. 5. MOTIONS OF THE RETINA. 19 num was rubbed along the fpine of her back, and a dram of it was ufed as an enema; by this medicine a kind of drunken delirium was continued many hours , and when it ceafed the convulfions did not return ; and the lady continued well many years, except fome {lighter relapfes, which were relieved in the fame manner. Mifs H ,-tan accomplifhed young lady, with light eyes and hair, was feized with convulfions of her limbs, with hic- cough, and efforts to vomit, more violent than wmrds can ex- prefs ; thefe continued near an hour, and were fucceeded with a cataleptic fpafm of one arm, with the hand applied to her head ; and after about twenty minutes thefe Ipafms ceafed, and a talkative reverie fupervened for near another hour, from which no violence, which it w*as proper to ufe, could awaken her. Thefe periods of convulfions, hrft of the muf- cles, and then of the ideas, returned twice a day for feveral weeks ; and were at length removed by great dofes of opium, after a great variety of other medicines and applications had been in vain experienced. This lady was fubjetd to frequent relapfes, once or twice a year, for many years, and was as frequently relieved by the lame method. Mifs W , an elegant young lady, with black eyes and hair, had fometimes a violent pain of her fide, at other times a moft painful ftrangury, which were every day fucceeded by de- lirium; which gave a temporary relief to the painful fpafrns. After the vain exhibition of variety of medicines and applica- tions by different phyhcians, for more than a twelvemonth, fire was directed to take fome dofes of opium, which were gradually increafed, by which a drunken delirium was kepc tip for a day or two, and the pains prevented from returning. A flcfh diet, with a little wine or beer, inftead of the low regimen fhe had previqufly ufed, in a few weeks completely eftablifhed her health ; which, except a few relapfes, has continued for many years. 9. Lalfly, as. we advance in life all the parts of the body become more rigid, and are rendered Ms fufceptible of new habits of motion, though they retain thofe that were before eftabli/hed. This is fenfibly obferved by thofe who apply thenffelves late in life to mufic, fencing, or any of the me- chanic arts. In the fame manner may elderly people retain the ideas they had learned early in life, but find great diffi- culty in acquiring new trains of memory ; infomuch that in extreme old age we frequently fee a forgetfulnefs of the buh- nefs of vefterday, and at the fame time a circumftantial re- membrance of the amufements of their youth ; till at length E the 20 MOTIONS OF THE RETINA. Sect. III. 6 the ideas of recolleiSIion and adlivity of the body gradually ceafe together, — fuch is the condition of humanity ! — and nothing remains hut the vital motions and fenfations. VI. r. In oppofition to this dodfrine of the production o: our ideas, it may be afked, if fome of our ideas, like other animal motions, are voluntary, why can we not invent new ones, that have not been received by perception ? The an- Iwer will be better underftood after having perufed the iuc- ceeding fedtion, where it will be explained, that the mufculur motions likewife are originally excited by the ftimulus of bo- dies external to the moving organ; and that the will has only the power of repeating the motions thus excited. 2. Another objector may afk, Can the motion of an organ of fenfe rel'emble an odour or a colour ? To which I can onlv anfvver, that it has not been demonftrated that any of our ideas refemble the objedts that excite them ; it has generally been believed that they do not; but this fhall be difcufled at large in Sect. XIV. 3. There is another objedtion that at flrit view would feeir. lefs eafy to furmount. After the amputation of a foot or a finger, it has frequently happened, that an injury being offered to the flump of the amputated limb, whether from cold air, too great preffure, or other accidents, the patient has complained of a fenfation of pain in the foot or finger that was cut off. Dees not this evince that all our ideas are excited in the brain, and not in the organs of fenfe ? This objection is anfwered by obferving, that our ideas of the fhape, place, and folidity of our limbs, are acquired by our organs of touch and of light, which are fituated in our lingers and eyes, and not by any ienfations in the limb itl'elf. In this cafe the pain or fenfation which formerly has arifeit in the foot or toes, and been propagated along the nerves to the central part of the fenforium, was at the fame time accom- panied with a viiible idea of the fhape and place, and with a tangible idea of the folidity of the affedled limb : now, when thele nerves are afterwards affedfed by any injury done to die remaining flump with a fimilar degree or kind of pain, the ideas of the fhape, place, or folidity of the loll limb, return by af~ fociation ; as thefe ideas belong to the organs of light anc touch, on which they were firfl excited. 4. If you wonder what organs of fenfe can be excited into motion, when vou call up the ideas of wifdom or beneve lence, which Mr. Locke has termed abflracfed ideas ; I afk you by what organs of fenfe you firft became acquainted with thefe ideas ? And the anfwer will be reciprocal; tor it is certain Sect. IV. ANIMAL CAUSATION. 21 certain that all our ideas were originally acquired by our or- gans of fenfe ; for whatever excites our perception mu ft be external to the organ that perceives it, and we have no other inlets to knowledge but by our perceptions : as will be fur- ther explained in Section XIV. and XV. on the Productions and Gaffes of Ideas. VII. If our recollection or imagination be not a repetition of animal movements, I afk, in my turn, What is it? You tell me it coniifts of images or pictures of things. Where is this extenfive canvafs hung up ? or where are the numerous receptacles in which thofe are depofked ? or to what elfe in the animal fyftem have they any fimilitude ? That pleating picture of objects, reprefented in miniatiue , on the retina of the eye, feems to have given rife to this illu- ffve oratory ! It was forgot that this reprefentation belongs ra- ther to the laws of light, than to thofe of life ; and may with equal elegance be feen in the camera obfeura as in the eye , and that the picture vanifhes for ever, when the object is withdrawn. SECT. IV, LAWS OF ANIMAL CAUSATION. I. The fibres, which conftitttte the mufcles and organs of fenfe, poffefs a power of contraction. The circumftances attending the exertion of this power of contraction eon- ftitute the laws of animal motion ; as the circumftances at- tending the exertion of the power of attraction confti- tute the laws of motion of inanimate matter. II. The fpirit of animation is the immediate caufe of the contraction of animal fibres ; it reftdes in the brain and nerves, and is liable to general or partial diminution or accumulation. III. The ftimulus of bodies external to the moving organ is fne remote caufe of the original contractions of animal fibres. IV. A certain quantity of ftimulus produces irritation, which is an exertion of the fpirit of animation exciting the fibres into contraction. V. A certain quantity of contraction of animal fibres, if it be perceived at all, produces pleafure ; a greater or lefs quantity of contraction, if it be perceived at all, produces pain ; thefe conftitute fenfation. VI. A certain quantity of fenfation produces defire or a- verfion ; thefe conftitute volition. VII All animal motions which have occurred at the fame time, or in immediate fucceflion, become fo connected, that when 22 SENSORIAL FACULTIES. Sect. V. when cne of them is reproduced, the other has a tendency to accompany or fucceed it. When fibrous contractions iuc- ceed or accompany other fibrous contractions, the connec- tion is termed affociation ; when fibrous contractions fucceed fenforial motions, the connection is termed cauiation ; when fibrous 2nd feniorial motions reciprocally introduce each other, it is termed catenation of animal motions. All thele connec- tions are faid to be produced by habit, that is, by rrequent re- petition. Thele laws of animal cauiation will be evinced by numerous faffs, which occur in our daily exertions ; and v ill afterwards be employed to explain the more recondite phe- nomena of the production, growth, difeal'es, and decay of the animal lyfretn. SECT. V. OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM. X. Four fenforial powers. 2. Irritation, fenfation, volition, affociation defined. 3. Scnforial motions dijlinguijhed from fibrous motions. 1. THE fpirit of animation has four different modes of ac- tion ; or, in other words, the#nimal fenforium poffeffes four different faculties, which are occafionally exerted, and caufe all the contradfions of the fibrous parts of the body. Thefe are the faculty of caul'mg fibrous contractions in confequence of the irritations excited by external bodies, in confequence of the fenfations of plealure or pain, in confequence of volition, and in confequence of the affociations of fibrous contractions with other fibrous contractions, which precede or accompany them. Thefe four faculties of the fenforium during their inactive Hate are termed irritability, fenfibility, voluntarily, and affo- ciability ; in their active Rate they are termed as above, irri- tation, fenfation, volition, affociation. 2. Irritation is an exertion or change of feme extreme part of the fenforium refining m the mufcles or organs of fenfe, in confequence of the appulfes of external bodies. Sensation is an exertion or change of the central parts of the fenforium, or of the whole of it, beginning at iome of thofe extreme £>arts of it, which rel.de in the mulcles or organs of fenfe. Volition is an exertion or change of the central parts of the fenforium, or of the whole of it, terminating in lome of thofe extreme parts of it, which refide in the muicles or organs of fenfe. Association 2 3 Sect. VI. i. SENSORIAL FACULTIES. Association is an exertion or change of forae extreme part of the fenforium refiding in the mufcies or organs of fenfe, in confequence of fome ; antecedent or attendant fibrous contradfions. 3. Thefe four faculties of the animal fenforium may, at the time of their exertions, be, termed motions, without impropriety of language ; for we cannot pafs from a ffate of inienfibility or inadtion, to a Rate of feniibility or of exertion, without fome change of the fenforium, and every change includes motion. We (hall therefore fometimes term the above defcribed facul- ties fcnforial motions, to diftinguifh them from fibrous mo- tions ; which latter exprefllon includes the motions of the mufcies and organs of fenfe. The adtive motions of the fibres, whether thofe of the mufcies or organs of fenfe, are probably fimple contradfions ; the fibres being, again elongated by antagoniff mufcies, by cir- culating fluids, or fometimes by elaftic ligaments, as in the necks of quadrupeds. The fenforial motions, which • confti- tute the fenfations of pleafure or pain, and which conftitute volition, and which caufe the fibrous contradfions in confe- quence of irritation or of afTociation, are not here fuppofed to be fludfuations or refludfuations of the fpirit cf animation; nor are they fuppofed to be vibrations of revibrations, nor condenfations or equilibrations of it; but to be changes or motions of it peculiar to life. SECT. VI. OF THE FOUR CLASSES OF FIBROUS MOTIONS. I. Origin of fibrous contrafiions. II. Dijtribution of them into four claffes , irritative motions, fenfitive motions , voluntary motions , and qfifociate motions , defined. I. ALL the fibrous contradfions of animal bodies originate from the fenforium, and refolve themfelves into four claffes, cor- refpondent with the four powers or motions of the fenforium above defcribed, and from which they have their caufation. 1. Thefe fibrous contradfions were originally caufed by the irritations excited by objedfs, which are external to the moving organ. As the pulfations of the heart are owing to the irritations excited by the ifimulus of the blood ; and the ideas of perception are owing to the irritations excited by external bodies. 2. Eut as painful or pleafureable fenfations frequently ac- companied thofe irritations, by habit thefe fibrous contractions became caufcable by the fenfations, and the irritations ceafed » to 24 FIBROUS CONTRACTIONS. Sect. VI. 2. to be neceffary to their production. As the fecretion of tears iil grief is caufed by the fenfation of pain; and the ideas of ima- gination, as in dreams or delirium, are excited by the pleal'ure or pain with which they were formerly accompanied. 3. But as the efforts of the will frequently accompanied thefe painful or pleafureable fenfations, by habit the fibrous contrac- tions became caufeable by volition ; and both the irritations and fenfations ceafed to be neceffary to their production. As the deliberate locomotions of the body, and the ideas of recollection, as when we wall to repeat the alphabet backwards. 4. But as many of thefe fibrous contractions frequently ac- companied other fibrous contractions, by habit they became caufeable by their affociarions with them; and the irritations, fenfations, and volition, ceafed to be neceffary to their produc- tion. As the aCtions of the mufcles of the lower limbs in fenc- ing are affociated with thofe of the arms ; and the ideas of fug- geftion are affociated with other ideas, which precede or ac- ng carelefily the alphabet in its ufual II. We fhall give the following names to thefe four claffes of fibrous motions, and fubjoin their definitions. 1. Irritative motions. That exertion or change of the fen- forium, which is caufed by the appulfes of external bodies, either limply fubfides, or is fucceeded by fenfation, or it produces fibrous motions; it is termed irritation, and irritative motions are thofe contractions of the mufcular fibres, or of the organs of fenfe, that are immediately confeqycnt to this exertion or change of the fenforium. 2. Seniitive motions. That exertion or change of the fen- forium, which conflitutes pleafure or pain, either limply fub- fides, or is fucceeded bv volition, or it produces fibroHS motions ; it is termed fenfation, and the fenfitive motions are thofe con- tractions of the mufcular fibres, or of the organs of fenfe, that are immediately eonfequent to this exertion or change cf the fenforium. 3. Voluntary motions. That exertion or change of the fenforium, which conftitutes defire or averfion, either fimplv fubfides, or is fucceeded by fibrous motions ; it is then termed volition, and voluntary motions are thofe contractions of the mufcular fibres, or of the organs of fenfe, that are immediately eonfequent to this exertion or change of the fenforium. 4. Affociate motions. That exertion or change of the len- forium, which accompanies fibrous motions, either fimplv fub- fides, or is fucceeded by fenfation or volition, or it produce^ other fibrous motions ; it is then termed affociation, and the affociate Sect. VII. i. IRRITATIVE MOTIONS. 25 affociate motions are thofe contractions of the mufculav fibres, or of the organs of ienfe, that are immediately consequent to this exertion or change of the fenforium. SECT. VII. OF IRRITATIVE MOTIONS. I. I. Son ie mufcular motions are excited by perpetual irrita- tions. 2. Others more frequently by fenfations. 3. Others by volition. Cafe of involuntary f retches in -paralytic limbs. 4. Some fenfual motions are excited by perpetual irritations. 5. Others more frequently by fenjation or volition. II. I. Mufcular motions , excited by perpetual irritations , occafonally become obedient to fenjation and to volition. 2 . And the fenfual motions. III. I. Other mufcular motions are affociated with the irri- tative ones. 2 . And other ideas with irritative ones. Of letters, language , hieroglyphics. Irritative ideas exijl ■without our attention to them. 1. 1. MANY of our mufcular motions are excited by per- petual irritations, as thofe of the heart and arterial fyftem by the circumfluent blood. Many other of them are excited by inter- mittent irritations, as thofe of the Stomach and bowels by the aliment we fwallow; of the bile-du6ts by the bile; ot the kid- neys, pancreas, and manv other glands, by the peculiar fluids they Separate from the blood ; and thofe of the lacteal and othei" abforbent veflels by the chyle, lymph, and moifture of tire atmofphere. Thefe motions are accelerated or retarded, as their correspondent irritations are increafed or diminished, without our attention or confcioufnefs, in the fame manner as the various Secretions of fruit, gum, refin, wax, and honey, are produced in the vegetable world, and as the juices of the earth and the moifture of the atmofphere are abforbed by their roots and foliage. 2. Other mufcular motions, that are moft frequently con- nected with our fenfations, as thofe of the fphindters of the bladder and anus, and the mufeuli eredtores penis, were ori- ginally excited into motion by irritation, for young children make water, and have other evacuations without attention to thefe circumffances ; “ et primis etiam ab incunabulis tendun- ter frepius puerorum penes, amore nondum expergefaCto.” So the nipples of young women are liable to become turgid by irritation, 26 IRRITATIVE MOTIONS. Sect. VII. i, irritation, long before they are in a fituation to be excited by the pleafure of giving milk to the lips of a child. 3. The contractions of the laiger muicles of our bodies, that are mod frequently connefted with volition, were origi- nally excited into aCtion by internal irritations ; as appears from the ftretching cryawning of all animals after long C cep. In the beginning of fome fevers this irritation of the mufcles produces perpetual ftretching and yawning ; in other periods of fever an univerfal reftleffnefs arifes from the fame caufe, the patient changing the attitude of his body every minute. The repeated ftruggles of the fcetus in the uterus rnuft be ow- ing to this internal irritation : for the foetus can have no other inducement to move its limbs but the toedium or irkfomenefs of a continued pofture. The following cafe evinces, that the motions of ftretching the limbs after a continued attitude are not always owing to the power of the will. Mr Dean, a mafon, of Auftry in Leicefterfhire, had the fpine of the third vertebra of dre back inlarged ; in fome weeks his lower extremities became feeble, and at length quite paralytic : neither die pain of blifters, the heat of fomentations, nor the utmoft efforts of the will could produce the leaft motion in thefe limbs ; yet twice or thrice a day, for many months, his feet, legs, and thighs were affedl- ed, for many minutes, with forcible ftretchings, attended with the fenfation of fatigue ; and he at length recovered the ul'e of his limbs, though the fpine continued protuberant. The fame circumftance is frequently feen in a lefs degree in the common hemiplagia ; and when this happens, I have believed repeated and ftrong fliocks of electricity to have been of great advantage. 4. In like manner the various organs of fenfe are originally excited into motion by various external ftimuli adapted to this purpofe, which motions are termed perceptions or ideas ; and .many of thefe motions, during our waking hours, are excited by perpetual irritation, as thofe of the organs cl hearing and of touch. The former by the conftant low indiftind noifes that murmur around us, and the latter by the weight of our bodies on the parts which iupport them ; and by the unceaftng varia- tion? of the heat, moitiure, and preffure of the atmoiphere ; and thefe fenfual motions, pteciiely as the mufeuiar ones above men- tioned, obey their correfpondent irritations without our atten- tion or conlcioufneis. 5. Other claffes of our ideas are more frequently excited by our fenfations of pleafure or pain, and others by volition: but that theie have all been originally excited by ftimuli from ex- ternal Sect. VII. 2.3. IRRITATIVE MOTIONS. 27 ternal objedls, and only vary in their combinations cr repara- tions, has been fuilv evinced by Mr. Locke; and are by him termed the ideas of perception, in contradiftindfioa to thofe which he calls the ideas of reflection. II. 1. Thefe mufcular motions, that are excited by perpe- tual irritation, are neverthelefs occalionally excitable by the fenfations of pleafnre or pain, or by volition, as appears by the palpitation of the heart from fear, the increaled lecredon of ialiva at the light of agreeable food, and the glow on the fkin of thofe who are afhamed. There is an inftance told in the Philofophical Tranfadfions, of a man, who could for a. time flop the motion of the heart when he plealed ; and Mr. D. has often told me, he could io far increafe the periftaltic: motion of his bowels by voluntary efforts, as to produce an evacuation by ftool at any time in half an hour. 2. In like manner the fenfuai motions, or ideas, that are excited by perpetual irritation, are nevertheless occalionally excitable by fenfation or volition ; as in the night,- when we liften under the influence of fear, or from voluntary attention, the motions excited in the organ of hearing by the whifper- ing of the air in our room, the pulfation of our own arteries, of the faint beating of a diftant watch, become objedts o£ perception. III. 1. Innumerable trains or tribes of ether motions are a (foci a ted with thefe mufcular motions, which are excited by irritation ;■ as by the ftimulus of the blood in the right cham- 1 her of the heart, the lungs are induced to expand themfelyes ; and the pedforal and intercoftal mulcles, and the diaphragm, adl at the fame time by their aflociations with them. And when the pharinx is irritated by agreeable food, the mufcles of deglutition are brought into adfion by affcciation. Thus when a greater light fails on the eye, the iris is brought into adfion without our attention ; and the ciliary procefs, when the focus is formed before or behind the retina, by their aflfo- ciations with the increased irritative motions of the organ of ' ifion. Many common actions of life are produced in a funilar manner. If a fly fettle on my forehead, w hi 1ft I am intent on tr.y prelent occupation, I difledge it with my finger without ex- citing my attention or breaking the train of my ideas. 2. In like manner the irritative ideas luggeft to us many other trains or tribes of ideas that are aflfociated with them. On this kind of eonnedfion, language, letters, hieroglyphics, and every kind of fymbol, depend. The fymbols themlelves produce irritative ideas, or fenfuai motions, which v\e do not attend to ; and other ideas, that are iucceeded by fenlation, F are 28 SENSITIVE MOTIONS. Sect. VIII. r, are excited by their affociation with them. And as thefe irri- tative ideas make up a part of the chain of our waking thoughts, introducing other ideas that engage our attention, though themfelves are unattended to, we find it very difficult to inveftigate by what fteps many of our hourly trains c: ;deas gain their admittance. It may appear paradoxical, that ideas can exift, and not be attended to • but all our perceptions are ideas excited by irri- tation, and lucceeded by fenfation. Now, when thefe ideas, excited by irritation, give us neither pleafure nor pain, we ceale to attend to them. Thus whilft: I am walking through that grove before my window, I do not run againft the trees or the benches, though my thoughts are ftrenuoufly exerted on fome other objedl. This leads us to a dillindf knowledge of irrita- tive ideas ; for the idea of the tree or bench, which I avoid, exifts on my retina, and induces, by affociation, the action of certain locomotive mufcles ; though neidrer itfelf, nor the actions of thofe mufcles, engage my attention. Thus, whilft we are converting on this fulfiedt, the tone, note, and- articulation of every individual word forms its cor- refpondent irritative idea on the organ of hearing ; but we on- ly attend to the affociatcd ideas, that are attached bv habit to thefe irritative ones, and are fucceedcd by fenfation : thus when we read the words “ printing-press/’ we do not attend to the fhape, fize, or exiftence of the letters which compofe thefe words, thougir each of them excites a correl'- pondent irritative motion of our organ of vilion ; but they introduce by affociation our idea of the mod; ufeful of modern inventions ; the capacious refervoir ot human knowledge, whole branching dreams diffufe fciences, arts, and moruiitv, through all nations and all ages. SECT. VIII. OF SENSITIVE MOTIONS. I. i. Senftive mufcular motions were originally excited into aiiion by irritation. 1. And fenjitive fenjual motions, ' ideas cf imagination, dreams. II. I. Senjitive mufcular motions are occcf anally obedient to volition. 2. And fenjitive fenfual motions. III. I. Other mufcular mo- tions are aff'oeiated with the fenjitive ones . 2. And ether Jenfual motions. I. i. MANY of the motions of our mufcles, that are ex- cited. into action by irritation, are at tire lame time accompa- nied 29 Sect. VIII. 2. SENSITIVE MOTIONS. nied with painful or pleafurable fenfations ; and at length be- come by habit caufable by the fenfations. Thus the motions of the fphindters of the bladder and anus were originally ex- cited into action by irritation : for. young children give no at- tention to thefe evacuations but as foon as they become len- fible of the inconvenience of obeying theie irritations, they fuffer the water or excrement to accumulate, till it ditagreea- biy affedts them ; and the action of thofe fpindlers is then in confequence of this dilagreeable fenlation. So the fecretion of the ialiva, which in young children is copioufly produced by irritation, and drops from their mouths, is frequently at- tended with the agreeable fenfation produced by the maftication of tafteful food ; till at length the fight of fuch food to a hun- gry perfon excites into ad'tion thefe falival glands ; as is feen in the Havering of hungry dogs. The motions of thole muicles, which afe affedled by laf- civious ideas, and thofe which are exerted in finding, weep- ing, darting from fear, and winking at the approach of dan- ger to the eye, and at times the adfions of every large mufcle of the body, become caufable by our fenfations. And all thefe motions are performed with flrength and velocity in pro- portion to the energy of the fenfation that excites them, and the quantity of fenforial power. 2. Many of the motions of our organs of fenfe, or ideas, that were originally excited into aftion by irritation, become in like manner more frequently caufable by our fenfations of pleafure or pain. Thefe motions are then termed the ideas cf imagination, and make up all the fcenery and tranfactions of our dreams. Thus, when any painful or pleafurable fenfations pofTefs us, as of love, anger, fear; whether in our fleep or waking hours, the ideas, that have been formerly excited by the objedfs of thefe fenfations, now vividly recur before us- by their connection with the fefenfations themfelves. So the fair fmiling virgin, that excited your love by her prefence, whenever that fenfation recurs, rifes before you in imagination ; and that with all the pleafing circumftances that had beiore engaged your attention. And in fleep, when you dream under the influ- ence of fear, all the robbers, fires, and precipices, that you for- merly have feen or heard of, arife before vou with terrible viva- city. All thefe fenfual motions, like the mufcular ones above mentioned, are performed with Strength and velocity in propor- tion to the energy of the fenfation of pleafure or pain which excites them, and the quantity of fenforial power. II. 1. Many of thefe mufcular motions above deferibed, that are moft frequently excited by our fenfations, are nevertheless occaiionally VOLUNTARY MOTIONS. Sect. IX. 3 ° occafionally caufable by volition; for we can fmile or frown fpontaneoufly, can make water before the quantity or acrimony of the urine produces a di ('agreeable fenfacion, and can volun- tarily mafticate a naufeous drug, or fwallow a bitter draught, though, our fenfation would flrongly diffuade us. 2. In like manner the lenfual motions, or ideas, that are mod frequently excited by our fenfations, are neverthelefs occaf. on- ally caufable by volition, as we can fponraneoullv call up our lull night's cream before us, tracing it induftriouflv, ftcp bv Itep, through ail its variety of fcenery and tranfaction ; or can volun- tarily examine or repeat the ideas that have "been excited by our difguft or admiration. III. i. Innumerable trains or tribes of motions are aff icicvd with thefe fendtive mufcular motions above mentioned ; as when a drop of water falling into the wind-pipe difagreeably affefts the air-veffels of the lungs, they are excited into violent action and with thefe fenfitive motions are a Hoc i a ted die actions of the pectoral and intercoftal mufcles, and the diaphragm ; tiil by their united and repeated fuccuffions, the drop is returned through the larinx. The fame occurs when any thing diiagreeablv affcifts the noitriis or the ftomach, cr the uterus : variety of mufcles are excited by affociation into forcible action, not to be fuppreffed by the utmoft efforts of the will; as in fneezing, vomitipg, and parturition. 2 . In like manner with thefe fenfitive fenfual motions, cr ideas of imagination, are affociated many ether trams or t rib ex cf ideas, which by fome writers ct metaphyfics have been chile i under the terms of relemblance, caufation, and contiguity ; and will be more iully treated of hereafter. SECT. IX. OF VOLUNTARY MOTIONS. I. I. Voluntary mufcular motions are originally excited hy irritations. 2. And voluntary' ideas. Gf reafon. II. i. Voluntary mufcular motions are occajionally caufable by fenfatlons. 2. And voluntary ideas. 1IJ, I. Voluntary mufcular motions’ are occafionally obedient to irritations. 2. And voluntary ideas. IV. I. Voluntary mufcular mo- tions are affociated with other mufcular motions. 2. And voluntary ideas. WHEN pleafure or pain affect the animal fvftem, many of its motions, both mufcular and fenfual, are brought into ac - don; as was ihewn in the preceding lection, and were caikd ' ' ' • ' ' fenfitive Sect. IX. i. VOLUNTARY MOTIONS. 31 fenfitive motions. The general tendency of thefe motions is to arreft and to poffefs the pleafure, or to diflodge or avoid the pain : but if this cannot immediately be accompli hied, defire or averfion are produced, and the motions in confequence of this new faculty of the fenforium are called voluntary. 1. 1 . TholVmufcles of the body that are attached to bones, have in general their principal connection with volition; as, I move my pen or raife my body. Thefe motions were origi- nally excited by irritation, as was explained in the lection cn that lubjecV, -afterwards the fenlations of pleafure or pain, that accompanied the motions thus excited, induced a repeti- tion of them; and at length many of them were voluntarily pradtifed, in iucceffion or in combination, for the common pur- pofes of life, as in learning to walk, or to fpeak ; and are performed with ftrength and velocity in proportion to the pnergy of the volition that excites them, and the quantity of feniorial power. 2. Another great clafs of voluntary motions confifls of the ideas of recolledtionl We will to repeat a certain train of ideas, as of the alphabet backwards ; and if any ideas, that do not belong to this intended train, intrude themfelves by other connections, we will to rejedf them, and voluntarily perfifl in the determined train. So at my approach to ahoufe which I have but once vifited, and that at the diftance of ma- ny months, I will to recollect the names of the numerous fa- mily I expedl to fee there, and I do recollect them. On this voluntary recollection of ideas our faculty of rea- fon depends, as it enables us to acquire an idea of the diffi- rnilicude of any two ideas. Thus if you voluntarily produce the idea of a right-angled-triangle, and then of a fquare ; and after having excited thefe ideas repeatedly, you excite the idea of their difference, which is that of another right-angled-tri- angle inverted over the former ; you are f aid to reafon upon this fubjeft, or to compare your ideas. Thele ideas of recollection, like the mufcular motions a- bove mentioned, were originally excited by the irritation of external bodies, aqd were termed ideas of perception : after- wards the p.eafu re or pain, that accompanied thefe motions, induced a repetition of them in the abfence of the external bo- dy, by which they were firft excited : and then they were termed ideas of imagination. At length they became volun- tarily practiied, in iucccffioji or in combination, for the com- mon purpofes of life; as when we make ourfelves matters of the hiftory of mankind, cr of the fciences they have invefti- gated ; and are then called ideas of recollection ; and are per- formed S 2 VOLUNTARY MOTIONS. Sect. IX. formed with ftrength and velocity in proportion to the energy of the volition that excites them, and the quantity of fenforial power. II. i. The mufcular motions above defcribed, that are moft frequently obedient to the will, are neverthelefs occa- fionally caufable by painful or pleafurable fenfation, as in the flatting from fear, and the contradtion of die calf of the leg in the cramp. 2 . In like manner the fenfual motions, or ideas, that are moft frequently connected with volition, are neverthelefs oc- Caftonaliy caufable by painful or pleafurable fenfation. As the hiftories of men, or the defcription of places, which we have voluntarily taken pains to remember, fometimes occur fo us in our dreams. III. i. The mufcular motions that are generally fubfervi- erit to volition, are alfo occafionally caulabie by irritation, as in ftretching the limbs after deep, and yawning. In this man- ner a contradtion ot the arm is produced by palling the elec- tric fluid from the Leyden phial along its mufcles ; and that even though the limb is paralytic. The fudden motion of the arm produces a difagreeable fenfation in the joint, but the mufcles feem to be brought into adtion Amply by irritation. 2 . The ideas, that are generally fubfervient to the will, are in like manner occafionally excited by irritation; as when we view again an objedt, we have before well ftudied, and often re- collected. IV. i. Innumerable trains or tribes of motions are aflbciated with thefe voluntary mufcular motions above mentioned ; as when I will to extend my arm to a diftant objedt, lome other mufcles are brought into action, and preferve the balance of mv body. And when I with to perform any fteadv exertion, as in threading a needle, or chopping with an ax, the pectoral mufcles are at the fame time brought into adtion to preferve the trunk of the body motionlefs, and we ceafe to reipire for a time. 2. In like manner the voluntary fenfual motions, or ideas, of recolledtion, are affociated with many other mains or tribes of ideas. As when I voluntarily recoiled! a Gothic window, that I faw fome time ago, the whole front of the cathedral occur, to me at the fame time. SECT. Sect. X. i. ASSOCIATE MOTIONS. U SECT. X. OF ASSOCIATE MOTIONS. I. X. Many mufcular motions, excited by irritations in trains or tribes, become affiociatecl. 2. And many ideas. II. i» Many fenjitive mufcular motions become officiated. 2 . And many fenjitive ideas. III. I. Many voluntary muf- cular motions become affiociated. 2. And then become obe- dient to fenfation or irritation. 3. And many voluntary ideas become ajjociated. ALL the fibrous motions, whether mufcular or fenfual, which are frequently brought into adtion together, ' either in combined tribes, or in fueeeffive trains, become fo connedted by habit, that when one of them is re-produced, the others have a tendency to fucceed or accompany it. 1. 1. Many of our mufcular motions were originally excited in fucceflive trains, as the contradlions of the auricles and of the ventricles of the heart ; and others in combined tribes, as the various divifions of the mufcles which compofe the calf of the kg, which were originally irritated into fynchronous adtion by the tedium or irkfomenefs of a continued pofture. By fre- quent repetitions thefe motions acquire affociations, which continue during our lives, and even after the deftruction of the greateft part of the fenforium; for the heart of a viper or frog will continue to puifate long after it is taken from the body ; and when it has entirely ceafed to move, if any part of it is goaded with a pin, the whole heart will again renew its pulfa- tions. This kind of connedtion we ihall term irritative afTociation, to diftinguifh it from fenfitive and voluntary, affo- ciations. 2. In like manner many of our ideas are originally excited in tribes ; as all the objedts of fight, after we become fo well acquainted with the laws of vilion as to diilinguifh figure and diftance as well as colour; or in trains, as while we pafs along, the objedts that furround us. The tribes thus received by irritation become affociated by habit, and have been termed complex ideas, by the writers of metaphylics, as this book, or that orange. The trains have received no par- ticular name ; but thefe are alike affociations of ideas, and fre- quently continue during our lives. So the tafte of a pine- apple, though we eat it blindfold, recalls the colour and fhape ot it; and we can fcarcely think on folidity without a figure. II. 1. By the various efforts of our fenfations to acquire or avoid their objedts, many mufcles are daily brought into lucceffive ASSOCIATE MOTIONS. 33 - Sect. X. 5. fucceffivo or fynchronous actions ; thefe become affbciated by habit, and are then excited together with great facility, and in many inftances gain indiffoluble connections. So the play of puppies and kittens is a reprel'entation of their mode of lighting, or of taking their prey ; and the motions of the muf- cles neceffary for thole purpofes, become alTociated by habit, and gain a great adroitnefs of action by thefe early repeti- tions : fo the morions of the abdominal mufcles, which were originally brought into concurrent aftion with the protrufive motion of the rectum or bladder by fenfation, become fo con- joined with them by habit, that they not only ealily obey thefe fenfations occafioned by the hamulus of the excrement and urine, but are brought into violent and unreftrainable ac- tion in the ftranguary and tenefmus. This kind of connec- tion we {hall term fenfitive affociation. 2. So many of our ideas, that have been excited together or in iucceffion by our fenfations, gain lynchronous or lucceffive affociations, that are fometimes indiffoiuble but with life. Hence the idea of an inhuman or difhonourable action perpe- tually calls up before us the idea of the wretch that was guilty of it. And hence thole unconquerable antipathies are formed, which fome people have to the fight of peculiar kinds of food, of which in their infancy they have eaten to excels or by confcraint. III. 1. In learning any mechanic art, as mufic, dancing, or the ufe of the fword, we teach many of our mulclcs to aft together or in lucceflion, bv repeated voluntary efforts ; which by habit become formed into tribes or trains ot affociation, and lerve ail our purpofes with great facility, and in fome in- ftances acquire an indffbluble union. Thefe motions are gradually formed into a habit of acting together by a multi- tude of repetitions, whilft they are yet feparatelv caufable bv the will, as is evident from the long time that is taken up by children in learning to walk and to ipeak; and is experi- enced by every one when he firffc attempts to fkate upon the icc or to fwim ; thefe we (hall term voluntary affociations. 2. All thele mul'cular movements, when they are thus uffo- ciated into tribes or trains, become afterwards not only obedi- ent to volition, but to che fenfations and irritations; and the fame movement compofes a part ot manv different tribes cr trains of motion. Thus a litigle muicle, when it ufe ai con- fort with its neighbours, on one fide, affifts to move the .ur.r in one direction; and in another, when it acts with thofe ... its neighbourhood on die other fide ; and in otlier direct) om. when it aits feparately or jointly with thole beat Le immcCi- ASSOCIATE MOTIONS. Sot. X. 3. 35 ately under or above it ; and all thefe with equal facility after their affociations have been well eftablifhed. The facility with which each mufcle changes from one af- fociated tribe to another, and tlvt either backwards or for- wards, is well obfervable in the mulcles of the arm in moving the windlafs of an air-pump ; and the flownefs of thofe mufcu- lar movements, that have not been affociated by habit, may be experienced by any one, who fhall attempt to faw the air quick perpendicularly with one hand, and horizontally with the other at the fame time, 3. In learning every kind of fcience, we voluntarily affoci- ate many tribes and trains of ideas, which afterwards are ready for all the purpofes, either of volition, fenfation, or irritation; and in feme inffances acquire indiffoluble habits of adting to- gether, fo as to affedt out reafoning and influence our actions. Hence the neceffity of a good education. Thefe affociate ideas are gradually formed into habits of adting together by frequent repetition, while they are yet fepa- rately obedient to the will ; as is evident from the difficulty we experience in gaining fo exadt an idea of the front of St. Paul’s church, as to be able to delineate it with accuracy, or in re- colledting a poem of a few pages. And thefe ideas, thus affociated into tribes, not only make up the parts of the trains of volition, fenfation, and irritation ; but the fame idea compofes a part of many different tribes and trains of ideas. So the fimple idea of whitenefs compofes a part of the complex idea of fnow, milk, ivory ; and the complex idea of the letter A compofes a part of the feveral affociated trains of ideas, that make up the variety of words, in which this letter enters. The numerous trains of thefe affociated ideas are divided by Mr. Hume into three claffes, which he has termed contiguity, caufation, and refemblance. Nor fhould we wmnder to find them thus connedted together, fmee it is the bufmefs of our lives to difpofe them into thefe three claffes ; and we become valuable to ourfelves and our friends, as we fucceed in it. Thofe who have combined an extenfive clafs of ideas by the contiguity of time or place, are men learned in the hillcry of mankind, and of the fciences they have cultivated. Thefe who have connedted a great clafs of ideas of refemblances, poffefs the fource of the ornaments of poetry and oratory, and of all rational analogy. While thofe who have connedted great claffes of ideas of caufation, are furnifhed with the powers of producing effedts. Thefe are the men of adtive wif- G dom, SENSORIAL ACTIONS. Sect. XI. i 36' dom, who lead armies to vidtory, and kingdoms to profperitv , or difcover and improve the fciences, which meliorate and adorn the condition of humanity. SECT. XL ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS. L Stimulation is of various kinds, adapted to the organs of fenfe, to the mufcles, to hollow membranes and gland 's. Some objects irritate our fenfes by repeated impulfes. II. I. Senjation and volition frequently affedt the whole fen- forium. 2. Emotions, paffons, appetites. 3. Origin of defire and dverfion. Criterion of voluntary aftions, dif- ference of brutes and men. 4. Senfbility and voluntari- ly. III. ykffociations formed before nativity \ in itative motions mijlakcn for affociated ones. Irritation. I. THE various organs of fenfe require various kinds of Simulation to excite them into adtion; the particles of light penetrate the cornea and humours of the eye, and then irritate the naked retina ; fapid particles, diffolved or diffufed in water or faliva, and odorous ones, mixed or combined with the air, irritate the extremities of the nerves of tafte and finell ; which either penetrate or are expanded on the membranes of the tongue and noftrils ; the auditory nerves are {Emulated by the vibrations of the atmofphere, communicated by means of the tympanum and of the fluid, whether of air or of water, behind it; and the nerves of touch by the hardnefs of furrounding bo- dies, though the cuticle is interpofed between thefe bodies and the medulla of the nerve. As the nerves of the fenfes have each their appropriated ob- jects, which {Emulate them into activity ; fo the muicular fibres, which are the terminations of other fets of nerves, have their peculiar objects, which excite them into adtion ; the lon- gitudinal mufcles are {Emulated into contrsdtion by extenfion, whence the ftretching or pendiculation after a long continued pofture, during \ hich they have been kept in a Rate of exten- sion ; and the hollow nauicles arc excited into adtion by diften- iion, as tbofe of the rectum and biadder are induced to protrude their contents from their fenfe of the ditlention, rather than of the acrimony of thofe contents. There Sect. XL 2. SENSORIAL ACTIONS. 37 There are other obiedfs adapted to ftimulate the nerves, which terminate in a variety of membranes, and thofe efpecial- ly which form the terminations of canals : thus the prepara- tions of mercury particularly afFedt the falivary glands, ipe- cacuanha affedfs the fphindter of the anus, cantharides that of the bladder, and laftly, every gland of the body appears to be ■induced with a kind of tafte, by which it (elects or forms each its peculiar fluid from the blood, and by which it is irritated into adfivity. Many of thefe external properties of bodies, which ftimu- •late our organs of fenfe, do not feem to affedf this by a Angle impulfe, but by repeated impulfes ; as the nerve of the ear is probably not excitable by a (ingle vibration of air, nor the optic nerve by a Angle particle of light ; which circumftance produces fome analogy between thofe two fenfes, at the fame rime the folidity of bodies is perceived by a Angle application ot a folid body to the nerves of touch, and that even through the cuticle ; and we are probably pofiefled of a peculiar fenfe to diftinguifti the nice degrees of heat and cold. The fenfes of touch and of hearing acquaint us with the me- chanical impadf and vibration of bodies ; thofe of fmell and tafte feem to acquaint us with fome of their chemical properties ; while the fenfe of vifton and of heat acquaint us with the ex- iftence of their peculiar fluids. Senfation and Volition. II. Many motions are produced by pleafure or pain, and that even in contradidfion to the power of volition, as in laugh- ing or in the ftranguary ; but as no name has been given to pleafure or pain, at the time it is exerted fo as to caufe Abrous motions, we have ufed the term fenfation for this purpofe ; and mean it to bear the fame analogy to pleafure and pain, that the word volition does to deAre and averfton. 1. It was mentioned in the ftfth Sedfion, that what we have termed fenfation is a motion of the central parts, or of the whole fenlorium, beginning at fome of the extremities of it. This appears, ftrft, becaufe our pains and pleafures are always caufed by our ideas or mufcular motions, which are the mo- tions of the extremities of the fenforium, And, fecondly, be- caufe the fenfation of pleafure or pain frequently continues fome time after the ideas or mufcular motions which excited it have ceafed : for we often feel a glow of pleafure from an agreeable reverie, for many minutes after die ideas, that were the fubjedt of it, have efcaped our memory , and frequently ex- perience SENSORIAL ACTIONS. Sect. XI. 2. 58 perience a dcjedfion of fpirits, without being able to affign the caule of it but by much recollection. When the fenforial faculty of defire or averfion is exerted f® as to caufe fibrous motions, it is termed volition ; which is laid in Sedb. V. to be a motion of the central parts, or of the whole fenforium, terminating in fome of the extremities of it. This appears, firft, becaufe our defires and averfions always terminate in recolledting and comparing our ideas, or in exert- ing our mufcles ; which are the motions of the extremities of the fenforium. And, fecondly, becaule delire or averlion be- gins, and frequently continues for a time in the central parts of the fenforium, before it is peculiarly exerted at the extremities of it ; for we fometimes feel defire or averfion without imme- diately knowing their objects, and in ccnfequence without im- mediately exerting any of our mufcular or fenfual motions to attain them: as in the beginning of the paflion of love, and perhaps of hunger, or in the ennui of indolent people. Though fenfation and volition begin or terminate at the extremities or central parts of the fenforium. yet the whole of it is frequently influenced bv the exertion of thefe faculties, as appears from their effects on the external habit ; for the whole Ikin is reddened by fhame, and an univerfal trembling is pro- duced by fear : and every mufcle of the body is agitated in angry people by die defire of revenge. There is another very curious circumftanee, which flhews that fenfation and volition are movements of the fenforium in contrary directions ; that is, that volition begins at the central parts of it, and proceeds to the extremities; and that fenfation begins at the extremities, and proceeds to the central parts : I mean, that thefe two fenforial faculties cannot be lirOngly ex- erted at the fame time ; for when we exert our volit: in ftrongly, we do not attend to nleaiure or pain ; and converfely, when we are ftrongly affedbed with the fenfation of pleafure or pain, we ufe no volition — As will be further explained in Section XVIII. on fleep, and Section XXXIV. on volition. 2. All our emotions and paflions feem to arile out of the exertions of thefe two faculties of the animal fenforium. Price, hope, joy, are the names of particular pleafures : fhame, aef- pair, forrow, are the names of particular pains : and love, am- bition, avarice, of particular deiires : hatred, difgufi, fear, anx- iety, of particular averfions. Whilft the paflion of anger in- cludes the pain from a recent injury, and the averfion to the adverfary that occaiioned it. And compaffion is the pain we experience at the fight of mifery, and the delire of relieving it. There SENSORIAL ACTIONS. Sect. XI. 2. 39 There is another tribe of defires, which are commonly termed appetites, and are the immediate confequences of the abfence of fome irritative motions. Thofe which arife from deleft of in- ternal irritations, have proper names conferred upon them, as hunger, thirft, luft, and the defre of air when our refpiration is impaired by noxious vhpours ; and of warmth when we are expoied to too great a degree of cold. But thofe, whole ft i- muli are external to the body, are named from die objefts which are by nature constituted to excite them; thefe deftres originate from our paft experience of the pleafurable fenfaticns they occaftcn, as the fmell of an hyacinth, or the tafte of a pine-apple. Whence it appears, that our pleafures and pains are at leaf as various and as numerous as our irritations ; and that our de- ftres and averftons lnuft be as numerous as our pleafures and pains. And that as fenfation is here ufed as a general terra tor our numerous pleafures and pains, when they produce tire contractions of our fibres ; fo volition is the general name for bur deftres and averftons, when they produce fibrous contrac- tions. Thus, when a motion of the central parts, or of the whole fenforium, terminates in the exertion of our mufcles, it is generally called voluntary aftion; when it terminates in the exertion of our ideas, it is termed recolleftion, reafon- ing, determining. 3. As the fenfations of pleafure and pain are originally in- troduced by the irritations of external objefts, fo our deftres and averftons are originally introduced by thofe fenfations ; for when the objects of our pleafures or pains are at a diftance, and we cannot inftantaneoufiy poffefs the one, or avoid the other, then defire or averfion is produced, and a voluntary ex- ertion of our ideas or mufcles fucceeds. The pain of hunger extites you to look out for food; the tree that {hades you prefents its odoriferous fruit before your eyes ; you approach, pluck, and eat. The various movements of walking to the tree, gathering the fruit, and maftic'ating it, are affbeiated motions introduced by their connection with fenfation ; but ifi from the uncom- mon height ot the tree, the fruit be inacceffible, and you are prevented from quickly pofleffing the intended pleafure, defire is produced. The confequence of this defire is, firft, a deli- beration about the means to gain the objedt of pleafure in pro- cels ot time, as it cannot be procured immediately ; and, iecond- ly, the mufeuiar aftion neceffary for this purpofe. Y on voluntarily call up all your ideas of caufation, that J ' are 4 C SENSORIAL ACTIONS. Sect. XI. 3. are related to the effe£t you defire, and voluntarily examine and compare fhem, and at length determine whether to afcend the tree, or to gather ftones from the neighbouring brook, is eafier to praCtife, or more promifing of fuccefs ; and, finally, you gather the ftones, and repeatedly fling them to diilodge the fruit. Hence, then, we gain a criterion to diftinguifh voluntary acfts or thoughts from thole caufed by fenfation. As the former are always employed about the means to acquire pleafui able objects, or the means to avoid painful ones ; while the latter are employed in the poiTtffion of thofe which are already in our power. Hence the activity of this power of volition produces tile great difference between the human and the brute creation. The ideas and the adtions of brutes are ahnoft perpetually em- ployed about their prefent pleafures or their prefent pains ; and, except in the few inftances which are mentioned in Sefb'on XVI. cn inftindt, they feldom bufy themfelves about the means of procuring future blifs, or of avoiding future mifery; fo that the acquiring of languages, the making of tools, and labouring for money, which are all only the means to procure pleafures, and the praying to the Deity, as another means to procure hap- pinefs, are charadteriftic of human nature. 4. As there are many difeafes produced by the quantity of the fenfation of pain or pleafure being too great or too little ; fo are there difeafes produced bv the fufeeptibility of die conftitu- tion to motions caufable by thefe fenlations being too dull or too vivid. This fufeeptibility ot the iyftem to feniitive motions is termed fallibility, to diftinguifli it from fenfation, which is the adtual exiftence or exertion of pain or pleafure. Other claffes of difeafes are owing to the exceffive promp- titude or fluggiflinefs of the conftitution to voluntary exertions, as well as to the quantity of defire or of averfion. This fuf- eeptibility of the fyftem to voluntary motions is termed volun- tarity, to diftinguifli it from volition, which is the exertion of defire or averfion : theie diieafes will be treated ot at length in the progrefs of the work. AJfociation . III. 1. It is not eafy to afiign a caufe, why thofe animal movements that have once occurred in fucceffion, or in com- bination, fhould afterwards have a tendency to fucceed or ac- company each other. It is a property of animation, and diftin- guiihes this order of being from the other productions of nature. . Wheu Sect. XII. OF STIMULUS AND EXERTION. 45 When a child firft wrote the word man, it was diftinguifh- ed in his mind into three letters, and thofe letters into many parts of letters ; but by repeated ufe the word man becomes to his hand in writing it, as to his organs of fpeech in pronounc- ing it, but one movement without any deliberation, or fenfa- tion, or irritation, interpofed between the parts of it. And as many feparate motions of our mufcles thus become united, and form, as it were, one motion ; fo each feparate motion before fuch union, may be conceived to confift of many parts or fpa- ces moved through ; and perhaps even the individual fibres of our mufcles have thus gradually been brought to aCt in con- cert, which habits began to be acquired as early as the very formation of the moving organs, long before the nativity of the animal ; as explained in SeCtiori XVI. 2. on inftinCt. 2. There are many motions of the body, belonging to the irritative clafs, which might, by a hafty obferver, be miftaken for affociated ones ; as the periftaltic motion of the ftomach and inteftines, and the contractions of the heart and arteries, might be fuppofed to be affociated with the irritative motions of their nerves of fenfe, rather than to be excited by the irritation of their mufcular fibres, by the diftention, acrimony, or momen- tum of the blood. So the diftention or elongation of mufcles by objeCts external to them, irritates them into contraction, though the cuticle or other parts may intervene between the ftimulating body and the contracting mufcle. Thus a horfe voids his excrement when its weight or bulk irritates the rec- tum or fphinCter ani. The motion of thefe mufcles aCt from the irritation of diftention, when he excludes his excrement; but the mufcles of the abdomen and diaphragm are brought into motion by affociation with thofe of the fphinCter and reCtum. SECT. XII. OF STIMULUS, SENSORIAL EXERTION, AND FI- BROUS CONTRACTION. I. Of fibrous contraction. 1. Two particles of a fibre cannot approach without the intervention of fomething, as in mag - netifm, electricity, elafiicity. Spirit of Ufe is not eledric ether. Galvan? s experiments, 2. Contraction of a fibre. 3. Relaxation fucceeds. 4. Succefjive contractions, with intervals. Quick pulfe from debility, from paucity of blood. W ?ak contractions peiformed in lefs time , and with Jhorter intervals . 42 OF STIMULUS AND EXERTION. Sect. XIL intervals. $. Lafl fituation of the fibres continues after contrarian. 6. Contrarian greater than ufual induces pleafure or pain. J. Mobility of the fibres uniform. Quantity of fenforial -power fluctuates. Confliiutes exci- tability. II. Of fenforial exertion, r. Animal motion in- cludes fiimulus , fenforial power, and contractile fibres. The fenfereial faculties aCt feparately or conjointly. Sti- mulus of four kinds. Strength and weaknefs defined. Senforial power perpetually exhaufied and renewed. M^eaknefs from defied of fiimulus. From defeCt of fenfo- rial power, the direCt and indirect debility of Dr. Brown. Why use become warm in Buxton bath after a time , and fee well after a time in a darkifh room. Fibres may ad violently, or with their whole force, and yet feebly. Great exertion m inflammation explained. Great mufcular force of fame infane people. 2 . Occafional accumulation of fenforial power in mufcles fubjedt to conflant fiimulus. In animals fileeping in winter. In eggs, feeds, f chirr ous tu- mours, tendons, bones. 3, Great exertion introduces pleafure or pain. Inflammation. Libration of the fyf- tem between torpor and activity. Fever-fits. 4. Defire and averfion introduced. Excefs of volition cures fevers. III. Of repeated fiimulus. I. A fiimulus repeated too fre- quently lofes effeCt. As opium, veins, grief. Hence old age. Opium and aloes in fmalt aofes. 2. A fiimulus not repeated too frequently does not lofe effeCt _ Perpetual movement of the vital organs. 3. A fiimulus repeated at uniform times produces greater effeCt. Imtaiion com- bined with affociation. 4. A fiimulus repeated frequently and uniformly may be withdrawn, and the aCtion of the organ will continue. Hence the bark cures agues, and flrengthens weak conflitutions. 5. DefeCt of fiimulus re- peated at certain intervals caufes fever-fits. 6. Stimu- lus long applied ceafcs to aCt a fecond time. 7. If a fii- mulus excites Inflation in an organ not uf tally excited into Inflation, inflammation is produced. IV. Ot llimu- lus greater than natural. 1. A fiimulus greater than na- tural diminifhes the quantity of fenforial power 'in gene- ral. 2 . In particular organs. 3. Induces the organ in- to [pa fnadic aClions. 4. Induces the antagonifi fibres in- to Ciion. C. Induces the organ into convul/ive or fixed fpafns. 6. Produces paralyfis of the organ. V. Ot fti- mains lefs than natural. 1. Stimulus lefs than natural occaflons accumulation of fenforial power in general. 2. In Sect. XII. i. OF STIMULUS AND EXERTION. 43 In particular organs , JluJIhng of the face in afrofly morn- ing. In fibres fubjeCt to perpetual Jlimulus only. Quantity of fenfor ial power inverfely as the ftmulus. 3. Induces pain. As of cold , hunger , head-ach. 4. Induces mere feeble and frequent contraClioni As in low fevers. Which are frequently owing to deficiency of fenforial power rather than to deficiency of Jhmulus. 5. Inverts fuccejfive trains of motion. Inverts ideas. 6. Induces paralyfis and death. VI. Cure of increafed exertion. 1. Natural cure of exhauflion of fenforial power. 2. Decreafe the irritations. VaneJeCtion. Cold. Abfli - nence. 3. Prevent the previous cold fit. Opium. Bark. Warmth. Anger. Surprife. 4. Excite Jome other part of the fy fern. Opium and warm bath relieve pains both from defedi and from exceefs of Jlimulus. 5. Firfl in- creafe the Jlimulus above, and then decreafe it beneath the natural quantity. VII. Cure of decreafed exertion. I. Natural cure by accumulation of fenforial power. Ague-fits. Syncope. 2. Increafe the Jlimulation, by wine , opium, given fo as not to intoxicate. Cheerful ideas. 3. Change the kinds of Jlimulus. 4. Stimulate the ajfociated organs. Bliflers of ufe in heart-burn, and. cold extremities. 5. Decreafe the jlimulation for a time , cold bath. 6. Decreafe the Jlimulation below natural , and, then increafe it above natural. Bark after emetics. Opium after vane fedtion. Practice of Sydenham in chlo- rojis. 7. Prevent unneceffary expenditure of fenforial power. Decumbent poflure, Jilence, darknefs. Pulfe quickened by rifing out of bed. 8. To the greatef degree of quiefeence apply the leaf fimulus. Otherwife para- lyfis or inflammation of the organ enfues. Gin, zvine , bliflers, defray by too great Jlimulation in fevers with de- bility. Intoxication in the flightefl degree fucceeded by debility. Golden rule for determining the befl degree of Jlimulus in low fevers. Another golden rule for deter- mining the quantity of fpirit which thofe who are debili- taded by drinking it may fafely omit. I. Of fibrous Contraction. 1. IF two particles of iron lie near each other, without mo- tion, and afterwards approach each other, it is reafonable to conclude that fomething befides the iron particles is the caufe of their approximation; this invifible fomething is termed magnetifm. In the fame manner, if the particles which com- pofe an animal raufcle do not touch each other in the relaxed H ftate 44 OF STIMULUS AND EXERTION. Sect. XII. r. Rate of the mufcle, and are brought into contaft during the contraftion of the mufcle ; it is reafonable to conclude that fome other agent is the caufe of this new approximation. For nothing can aft where it does not exift ; for to aft includes to exift ; and therefore the particles of the mul'cular fibre fwhich in its ftate of relaxation are fuppofed not to touch) cannot affeft each other without the influence of fome inter- mediate agent ; this agent is here termed the fpirit of animation, or fenforial power, but may with equal propriety be termed the power which caufes contraftion ; or may be called by any other name, which the reader may choofe to affix to it. The contraftion of a mufcular fibre may be compared to the following eleftric experiment, which is here mentioned, not as a philofophical analogy, but as an iiluftration or fimile to facilitate the conception of a difficult fubjeft. Let twenty very final! Leyden phials, properly coated, be hung in a row by fine fiik threads, at a fmall diftance from each other; let the in- ternal charge of c^ie phial be pofitive, and of the other nega- tive, alternately: if a communication be made from the internal furface of the firft to the external furface of the laft in the row, they will ail of them inftantly approach each other, and thus fhorten a line that might conneft them like a mufcular fibre. See Botanic Garden, p. i. Canto I. 1. 2C2, note onGymnotus. The attractions of eleftric’ty or of magnetifm do not apply philofophically to the iiluftration of the contraftion of animal fibres, fince the force of- thofe attractions increafes in fome proportion inverfely as the diftance ; but in mufcular motion there appears no difference, in velocity or ftrength, during the beginning or end of the contraftion, but what may be clearly aferibed to the varying mechanic advantage in the approxima- tion of one bone to another. Nor can mufcular motion be affimilated, with greater plaufability, to the attraction of cohe- fion or elafticity ; for in bending a fteel fpring, as a fmall fword, a lefs force is required to bend k the firft inch than'the fecond ; and die fecond than the third; the particles of fteel on the con- vex fide of the bent fpring endeavouring to reftore themfelves more powerfully the further they are drawn from each other. See Botanic Garden, p. i. addit. note XVIII. I am aware that this may be explained another way, by fup- ponng the elafticity of the fpring to depend more on the com- preffion of the particles on the concave fide, than on the exten- ftou of them on the convex lide ; and by fuppofing the elafticity of the elaftie gum to depend more on the refiitance to the late- ral compreffion of its particles, than to the longitudinal exten- iion of them. Neverthelefs, in mufcular contraftion, as above obferved. Sect. XII. i. OF STIMULUS AND EXERTION. 45 obferved, there appears no difference in the velocity or force of it at its commencement or termination ; from whence we muff conclude, that animal contraction is governed by laws of its own, and not by thofe of mechanics, chemiftry, magnetifm, or electricity. On thefe accounts I do not think the experiments conclufive, which were lately publilhed by Galvani, Volta, and ethers, to fliew a fimilitude between the fpirit of animation, which con- tracts the mufcular fibres, and the electric fluid: fence the electric fluid may act only as a more potent ftimulus, exciting the mufcular fibres into action, and not by fupplying them with a new quantity of the fpirit of life. Thus, in a recent hemi- plegia, I have frequently obferved, when the patient yawned and ftretched himfelf, that the paralytic limbs moved alfo, though •they were totally difobedient to the will. And when he was .electrified, by palling fhocks from the affected hand to the af- fected foot, a motion of the paralytic limbs was alio pVoduced. Now, as in the act of yawning the mufcles of the paralytic limbs were excited into action by the ftimulus of the irktomenefs of 4 continued pofture, and not by an additional quantity of the fpirit of life; fo we may conclude, that the paftage of the elec- tric fluid, which produced a fimilar effect, acted only as a fti- mulus, and not by fupplying any addition of fenfonal power. If, neverthelefs, this theory Ihould ever become eftablifhed, a ftimulus mull be called an eductor of vital ether ; which ftimu- lus may confift of fenfation or volition, as in the electric eel, as well as in the appulfes of external bodies ; and, by drawing off the charges of vital fluid, may occafion the contraction or motions of the mufcular fibres and organs of l'enfe. 2. The immediate effect of the action of the fpirit of anima- tion, or fenforial power, on the fibrous parts of the body, whe- ther it acts in the mode of irritation, fenfation, volition, or af- fociatiou, is a , contraction of the animal fibre, according to the fecond law of animal caufation. Sect. IV. Thus the fti- mulus of the blood induces the contraction of the heart ; the agreeable tafte of a ftrawberry produces the contraction of the mufcles of deglutition ; the effort of the will contracts the mufcles which move the limbs in walking ; and, by affoci- ation, other mufcles of the trunk are brought into contraction to preferve the balance of the body. The fibrous extremities of the organs ot fenfe have been {hewn, by the ocular fpectra in Sect. III. to fuffer fimilar contraction by each of the above modes of excitation; and by their configurations to conftitute our ideas. 3. After animal fibres have for fome time been excited into contraction, 46 OF STIMULUS AND EXERTION. Sect. XII. 1. contraction, a relaxation fucceeds, even though the exciting caufe continues to at. In refpect to the irritative motions, this is exemplified in the periftaltic contractions of the bow- els; which ceafe and are renewed alternately, though the fti- mulus of the aliment continues to be uniformly applied - } in the fenfitive motions, as in ftrangury, tenefmus, and parturition, the alternate contractions and relaxations of the mufcles exift, though the ftimulus is perpetual. In our voluntary exertions it is experienced, as no one can hang long by the hands, how- ever vehemently he wills fo to do ; and in the aflfociate motions* the conftant change of our attitudes evinces the necefiity of re- laxation to thofe mufcles which have been long in action. This relaxation of a mufcle, after its contraction, even though the ftimulus continues to be applied, appears to ariie from the expenditure or diminution of the fpirit of animation previoufly refident in the mufcle, according to the feccnd lave’ of animal caufation in Set. IV. In thofe conftitutions which are termed weak, the fpirit of animation becomes fooner exhaufted, and tremulous motions are produced, as in the hands of infirm peo- ple, when they lift up a cup to their mouths. This quicker exhauftion of the fpirit of animation is probably owing to a lefs quantity of it refiding in the ’a ting fibres, which therefore more frequently require a fupply from the nerves which be- long to them. 4. If the fenforial power continues to at, whether it ats in the mode of irritation, fenfation, volition, or affociation, a new contration of the animal fibfe fucceeds after a certain interval ; which interval is of fhorter continuance in weak people than in ftrong ones. This is exemplified in the fhak- ing of the hands of weak people, when they attempt to write. In a manufeript epiftle of one of my correfpondents, which is written in a fmall hand, I obferved from four to fix zigzags in the perpendicular ftroke of every letter, which fhews that both the contractions of the fingers, and intervals between them, rnuft have been performed in very fhort periods of time. The times of contraction of the mufcles of enfeebled people being lefs, and the intervals between thofe contractions being lefs alfo, accounts for the quick pulfe in fevers with debility, and in dying animals. The fliortnefs of the intervals between one contraction and another in weak conftitutions, is pro- bably owing to the general deficiency of the quantity of the fpirit of animation, and therefore there is a lefs quantity ot it to be teceived at each interval of the activity of the fibres. Hence, in repeated motions, as of the fingers in performing on the harpfichord, it would at firft fight appear, that fwiftnefs Sect. XII. i. OF STIMULUS AND EXERTION. 47 and ftrength are incompatible ; neverthelefs, the Angle contrac- tion of a mufcle is performed with greater velocity, as well as with greater force, by vigorous conllitutions, as in throwing a javelin. There is, however, another circumftance, which may often contribute to eaufe the quicknefs of the pulie in nervous fe- vers, as in animals bleeding to death in the flaughter-boufe, which is the deficient quantity of blood ; whence the heart is but half diftended, and in confequence fooner contrads. See Sed. XXXII. 2. 1. For we muft not confound frequency of repetition with quicknefs of motion, or the number of pulfations with the velocity, with which the fibres, which conftitute the coats of the arteries, contrad themfelves. For where the frequency of the pulfations is but feventy-five in a minute, as in health; the contrading libres, which conftitute the fides of the arteries, may move through a greater fpace in a given time, than where the frequency of pulfation is one hundred and fifty in a minute, as in feme fevers with great debility. For if in thofe fevers the arteries do not expand themfelves in their diaftole to more than half the ufual diameter of their diaftole in health, the fibres which conftitute their coats will move thiough a lefs fpace in a minute than in health, though they make two pulfations for one. Suppofe the diameter of the artery during its fyftole to be one line, and that the diameter of the fame artery during its diaftole, in health, is four lines, and in a fever, with great debi- lity, is only two lines — It follow^, that the arterial fibres con- trad, in health, from a circle of twelve lines in circumference to a circle of three lines in circumference ; that is, they move through a fpace of nine lines in length ; while the arterial fibres in the fever, with debility, would twice contrad from a circle of fix lines, to a circle of three lines ; that is, while they move through a fpace equal to fix lines. Hence, though the fre- quency- of pulfation in fever be greater, as two to one, yet the velocity of contradion in health is greater, as nine to fix, or as three to two. On the contrary, in inflammatory difeafes wdth ftrength, as in the pleurify, the velocity of the contrading fides of the arte- ries is much greater than in health ; for if we fuppofe the number of pulfations in a pleurify to be half as much more than in health ; that is, one hundred and twenty to eighty, (which is about what generally happens in inflammatory dif- eafes) and if the diameter of the artery in diaftole be one third greater than in hcplth, which I believe is near the truth, the ' refult 48 OF STIMULUS AND EXERTION. Sect. XII. j. refult will be, that the velocity of the contractile Tides of the ar- teries will be in a pleurify, as two and an half to one, compar- ed to the velocity of their contraction in a ftate of health ; for if the circumference of the fyftole of the artery be three lines, and the diaftole in health be twelve lines in circumfe- rence, and in a pleurify eighteen lines ; and fecondly, if the ar- tery pulfates thrice in the difeafed ftate for twice in the healthv one, it follows, that the velocity of contraction in die difeafed ftate to that in the healthy ftate, will be forty-five to eighteen, or as two and a half to one. From hence it would appear, that if we had a criterion to determine the velocity of the arterial contractions, it would at the fame time give us their ftrength, and thus be of more fer- vicein diftinguiihingdifeafes, than the knowledge of their fre- quency. As fuch a criterion cannot be had, the frequency of pulfation, the age of the patient being allowed for, will infome meafure alfift us to diftinguifli arterial ftrength from arterial debility; fince, in inflammatory difeafes, with ftrength, the fre- quency feldom exceeds one hundred and eighteen, or one hun- dred and twenty pulfations in a minute, unlefs under peculiar circumftances, as the great additional ftimuli of wine or of external heat. 5. After a mufcle or organ of fenfe has been excited into conti adlion, and the fenforial power ceafes to adt, the laft litu- htion or configuration of it continues, unlefs it be difturbed by the adlion of lome antagonift fibres, or other extraneous power. Thus, in weak or languid people, wherever they throw their limbs on their bed or fofa, there thev lie, till ano- ther exertion changes their attitude; hence one kind of ocular fpedtra feems to be produced after looking at bright objedts : thus, when a fire-ftick is whirled round in the night, there ap- pears in the eye a complete circle of fire, the adlion or configu- ration of one pare of the retina not ceafing before the return of the whirling fire. Thus, if any one looks at the fetting fun for a fliort time, and then covers his clofed eyes with his hand, he will, tor many feconds of time, perceive the image of the fun on his retina. A funilar image of all other bodies would remain l'ome time in the eye, but is effaced by the eternal change of the motions of the extremity of this nerve in our attention to other objedts. See Sedt. XVII. 1. 3. on fleep. Hence the dark l'pots, and other ocular fpedtra, are more frequently attended to, and re- main longer in the eyes of weak people, as after violent exer- cife, intoxication, or want of fleep. 6. A contradtion of the fibres fomewhat greater than ufual, introduces Sect. XII. i. OF STIMULUS AND EXERTION. 49 introduces pleafurable fenfation into the fyftem, according to the fourth law of animal caufation. Lienee the pleafure in the beginning of drunkennefs is owing to the increafed adfion of the fyftem from the ftimulus of vinous fpirit, or of opium. If the contractions be ftill greater in energy or duration, pain- ful fenfations are introduced, as in confequence of great heat, or cauftic applications, or fatigue. If any part of the fyftem, which is ufed to perpetual ac- tivity, as the ftomach, or heart, or the fine veflels of the fkin, adds for a time with lefs energy, another kind of painful fen- fation enfues, which is called hunger, or faintnefs, or cold. This occurs in a lefs degree in the locomotive mulcles, and is called wearifomenefs. In the tw.o former kinds of fenfation there is an expenditure of fenforial power ; in thefe latter there is an accumulation of it. 7. We have ufed the words exertion of fenforial power as a general term to exprefs either irritation, fenfation, volition, or afiociation ; that is, to exprefs the activity or motion of the fpirit of animation, at the time it produces the contractions of the fibrous parts of the fyftem. It may be fuppofed that' there may exift a greater or lefs mobility of the fibrous parts of our fyftem, or a propenfity to be ftimulated into contraction by the greater or lefs quanti ty or energy of the fpirit of animation ; and that hence, if the exertion of the fenforial power be in its natural ftate, and the mobility of the fibres be increafed,' the fame quantity of fibrous contractions will be caufed, as if the mobility of the fibres continues in its natural ftate, and the fenforial exertion be increafed. Thus it may be conceived, that in difeafes accompanied with ftrength, as in inflammatory fevers, with arterial ftrength, that the caufe of greater fibrous contradfion may exift in the in- creafed mobility of the fibres, whofe contradlions are thence both more forcible and more frequent. And that in difeafes attended with debility, as in nervous fevers, where the fibrous contradlions are weaker and more frequent, it may be con- ceived that the caufe confifts in a decreafe of mobility of the fibres; and that thofe weak conftitutions, which are attended with cold extremities and large pupils of the eyes, may pofiefs lefs mobility of the contradfiie fibres, as well as lefs quantity of exertion of the fpirit of animation. In anfwer to this mode of reafoning, it may be fufficient to obferve, that the contradfiie fibres conlift of inert matter ; and when the fenforial power is withdrawn, as in death, they pofiefs no power of motion at all, but remain in their laft ftate, whe- ther of contradfion or relaxation, and muff thence derive the whole 50 OF STIMULUS AND EXERTION. Sect. XII. x. whole of this property from the fpirit of animation. At the fame time it is not improbable, that the moving fibres of ftrong people may po fiefs a capability of receiving or containing a greater quantity of the fpirit of animation than thofe of weak people. In every contraction of a fibre there is an expenditure of the fenforial power, or fpirit of animation ; and where the ex- ertion of this fenforial power has been for fome time increaf- ed, and the mufcles or organs of fenfe have in confequence added with greater energy, its propenlity to activity is propor- tionally leflened; which is to be afcribed to the exhauftion or diminution of its quantity. On the contrary, where there has been lefs fibrous contraction than ufual for a certain time, the fenforial power, or fpirit of animation, becomes accumu- lated in the inactive part*of the fyftem. Hence vigour fuc- ceeds reft ; and hence the propenfity to action, of all our or- gans of fenfe and mufcles, is in a ftate of perpetual fluctuation. The irritability, for inftance, of the retina; that is, its quan- tity of fenforial power, varies every moment, according to the hriglftnefs orobfcurit.y of the object laft beheld, compared with the prefent one. The fame occurs to our fenfe ot heat, and to every part of our fyftem, which is capable of being excited into action. When this variation of the exertion of the fenforial power becomes much and permanently above or beneath the natural quantity, it becomes a difeafe. It the irritative motions be too great or too little, it thews that the ftimulus of external things afledls this fenforial power too violently or too inertly. It the fenfitive motions be too great or too little, the caule arifes from the deficient or exuberent quantity of fenfation produced in confequence of the motions of the mufcular fibres or organs of fenfe. If the voluntary acftions are diteafed, the caufe is to be looked for in the quantity of volition produced, in confequence of the defire or averfion occafioned by the painful or pleafur- able fenfations above mentioned. And the difeafes of afloci- ations probably depend on the greater or lets quantity of the other three fenforial powers by which they were formed. From whence it appears, that the propenfity to action, whe- ther it be called irritability, fenfibility, voluntarily, or afloci- abilitv, is only another mode of expreflion for the quantity of fenforial power, refining in the organ, to be excited. And that, on the contrary, the words irritability and infenfibiliry, toge- ther with inaptitude to voluntary and aflociate motions, are fynoniinous with deficiency of the quantity of fenforial power, or of the fpirit of animation, reliding in the organs to be ex- cited. Sect. XII.2. OF STIMULUS AND EXERTION. 51 II. Of fenforial Exertion. 1 . There are three circumftances to be attended to in the pro- duction of animal motions. I ft. The ftimulus. 2d. The fenforial power. 3d. The contraClile fibre. — 1 ft. A ftimu- lus, external to the organ, originally induces into aCtion the fenforial faculty termed irritation; this produces the contrac- tion of the fibres, which, if it be perceived at all, introduces pleafure or pain ; which, in their aCtive ftate, are termed fen- fation, which is another fenforial faculty, and, occafionally produces contraction of the fibres : this pleafure or pain is therefore to be confidered as another ftimulus, which may either aCt alone or in conjunction with the former faculty of the fenforium, termed irritation. This new ftimulus of plea- fure or pain either induces into aCtion the fenforial faculty, termed fenfation, which then produces the contraction of the fibres ; or it introduces defire or aveffion, which excite into aCtion another fenforial faculty, termed volition, and may therefore be confidered as another ftimulus, which either alone, or in conjunction with one or both ot the two former facul- ties of the fenforium, produces the contraction of animal fibres. There is another fenforial power, that of aftbciation, which perpetually, in conjuCtion with one or more of the above, and frequently fingly, produces the contraction ot animal fibres, and which is itielf excited into aCtion by the previous motions of contracting fibres. Now, as the fenforial power, termed irritation, refiding in any particular fibres, is excited into exertion by the ftimulus of external bodies aCting on tliofe fibres ; the fenforial power, termed fenfation, refiding in any particular fibres, is' excited into exertion by the ftimulus of pleafure or pain aCting on thofe fibres ; the fenforial power, termed volition, refiding in any particular fibres, is excited into exertion by the ftimulus of defire or averfion; and the fenforial power, termed affoci- ation, refiding in any particular fibres, is excited into aCtion by the ftimulus of other fibrous motions, which had frequent- ly preceded them. The word ftimulus may therefore be ufed, without impropriety of language, for any of thefe four Caufes, which excite the four fenforial powers into exertion. For though the immediate, caufe of volition has generally been termed a motive , and that of irritation only, has generally ob- tained the name of Jiimulus ; yet, as the immediate caufe which excites the fenforial powers of fenfation, or of aflocia- tion, into exertion, have obtained no general name, we {hall ufe the word ftimulus for them all. I Hence 5a OF STIMULUS AND EXERTION. Sect. XII. 2 : Hence the quantity of motion produced. in any particula part of the animal iyftem, will be as the quantify of ltimulus and the quantity of fenforial power, or fpirit of animation, te- nding in the contracting fibres. Where both thefe quantities are great ,jlrength is produced, when that word is applied to the motions ot animal bodies. Where either of them is defi- cient, weaknefs is produced, as applied to the motions of ani- mal bodies. Now, as the fenforial power, or fpirit of animation, is per- petually exbaufted by the expenditure of it in fibrous contrac- tions, and rs perpetually renewed by the fecretion or produc- tion of it in the brain and fpinal mar row, the quantity of ani- mal ftrength mud be in a perpetual ftate of fluctuation on this account ; and if to this be added tire unceafrng variation of all the four kinds of ftimulus above deferibed, which produce the exertion of the fenforial powers, the ceafelefs viciffitude of animal ftrength becomes ealily comprehended. If the quantity of fenforial power remains the fame, and the quantity of flimulus be leflened, a weaknefs of the fibrous con- tractions eniues, w'hich may be denominated debility from dcfctl of f imulus. If the quantity of flimulus remains the fame, and die quantity of fenforial power be leftened, anodier kind of weaknefs eniues, which may be termed debility from defett of fenforial power ; the tonner of thefe is called by Dr. Brown, in his Elements of Medicine, diredt debility, and the latter indirect debility. The coincidence ofTome parts of tin's work, with correfpondent deductions in die Brunonian Ele- menta Medicina, a werk (with fome exceptions) of great ge- nius, muft be confidered as confirmations of the truth of the theory, as diey were probably arrived at by different trains of reafoning. Thus, in thofe who have been expofed to cold and hunger, there is a deficiency ot ftimulus. While in nervous fever there is a deficiency of fenforial power : and in habitual drunk- ards, in a morning before their ulual potation, there is a defi- ciency both ot ftimulus and of fenforial power ; while, on the other hand, in the beginning of intoxication, there is an excefs of ftimulus: in the hot ach, after the hands have been immerf- ed in fnow, there is a redundancy of fenforial power; and in inflammatory difeafes w ith arterial ftrength, there is an excels of both. Hence, if the fenforial power be leffened, while the quantity of ftimulus remains the fame as in nervous fever, the frequen- cy of repetition of the arterial contractions mav continue ; but their lotcc. in relpect to removing obltacles, as in promoting the Sect. XII. 2. GF STIMULUS AND EXERTION. 53 the circulation of the blood, or the velocity of each contradtion, will be diminifhed ; that is, the animal {Length will be leflened. And, fecondly, if the quantity of fenforial power be lefiened, and the ftimulus be increafed to a certain degree, as in giving opium in nervous fevers, the arterial contradfions may be performed more frequently than natural, yet with lefs {Length. And thirdly,. if the fenforial power continues the fame in refpedt to quantity, and the ftimulus be fomewhat diminifhed, as in going into a darkifh room, or into a coldifh bath, lup- pofe of about eighty degrees of heat, as Buxton-bath, a tem- porary weaknefs of the affedfed fibres is induced, till an accu- mu.ation of fenforial power gradually fucceeds, and counter- balances the deficiency of ftimulus ; and then the bath ceafes to feel cold, and the room ceales to appear dark; becaufe the fibres of the fubcutaneous v-effels, or of the organs of feilfe, adf with their ufual energy. A .fet of mufcular fibres may thus be ftimulated into violent exertion; that is, they may act frequently, and with their whole fenforial power, but may neverthelels not adf ftrongly; becaufe the quantity of their fenforial power was originally fmall, or was previoufty exhaufted. Hence a ftimulus may he great, and the irritation in confequence adf with its full force, as in the hot paroxyfms of nervous fever; but if the fenforial power, termed irritation, be fmall in quantity, the force of the fibrous contradfions, and the times of their continuance in theli* con-'Tadted ftate, will be proportionally final!. In the fame manner, in the hot paroxyfm of putrid fevers, which are fhewn in Sedt. XXXIII. to be inflammatory fe- vers, with arterial debility, the fenforial power, termed fenfa- tion, is exerted with great adlivity ; yet the fibrous contrac- tions, which produce the circulation of the blood, are perform- ed without {Length, becaufe the quantity of fenforial power, then refiding in that part of the fyftem, is fmall. Thus, in irritative fever, with arterial ftrength, that is, with excefs of fpirit of animation, the quantity of exertion during the hot part of the paroxyfm, is to be eftimated from the quan- tity of ftimulus, and the quantity of fenforial pow r er; while in fenfttive (or inflammatory) lever, with arterial ftrength, that is, with excefs of fpirit of animation, the violent and for- cible adtions of the vafcular fyftem, during the hot part of the paroxyfm, are induced by the exertions of two fenforial powers, which are excited by two kinds of ftimulus. Thele are the fenforial power of irritation, excited by the ftimulus of bodies external to the moving fibres, and the fenforial power- ot 54 OF STIMULUS AND EXERTION. Sect. XII. 2. of fenfation, excited by the pain in confequence of the increafed contractions of thofe moving fibres. And in infane people, in fome cafes, the force of their muf- cular adtions will be in proportion to the quantity of fenforial power which they poffefs, and the quantity of the ftimulus of defire or averfion which excites their volition into aCtion. At the fame time, in other cafes, the ftimulus of pain or plea- fure, and the ftimulus of external bodies, may excite into ac- tion the fenforial powers ot fenfation and irritation, and thus add greater force to their mufcular adtions. 2. The application of the ftimulus, whether that ftimulus be fome quality of external bodies, or pleafure or pain, or de- fire or averfion, or a link of affociation, excites the corrcf- pondent fenforial power into action, and this caufes the con- traction of the libre. On the contraction of the fibre, a part of the fpirit of animation becomes expended, and the fibre ccai'es to contraCt, though the ftimulus continues to be applied, till, in a certain time, the fibre having received a lupply of fenfo- rial power, is ready to contract again, it the ftimulus conti- nues to be applied. If the ftimulus, on the contrary, be with- drawn, the fame quantity of quiefeent fenforial power becomes reiident in the fibre as before its contraction ; as appears from the readinefs for aCtion of the large locomotive mufcles ot the body, in a fhort time after common exertion. But in thofe mufcular fibres which are lubjeCt to conftant ftimulus, as the arteries, glands, and capillary vefiels, another phenomenon occurs, if their aecuftomed ftimulus be with- drawn ; which is, that the fenforial power becomes accumu- lated in the contraCtile fibres, owing to the want of its being perpetually expended, or carried away, by their ufual unre- rnitted contractions. And, on this account, thofe mufcular fibres become afterwards excitable into their natural aCtions by a much weaker ftimulus ; or into unnatural violence of ac- tion, by their aecuftomed ftimulus, as is feen in the hot fits of intermittent fevers, which are in confequence ot the previous cold ones. Thus the minute veflfels ot the (kin are conftant- ly ftimulated by the fluid matter of heat; it the quantity ot this ftimulus of heat be a while diminifhed, as in covering the hands with fnow, the veflels ceafe to adt, as appears from the palenels of the fkin ; if this cold application of fnow be conti- nued but a Abort time, the fenforial power, which had habitu- ally been fupplied to the fibres, becomes now accumulated ::i them, owing to the want of its being expended by their accul- tomed contractions. And thence a lei's ftimulus of heat will now excite them into violent contractions. Sect. XII. 2. OF STIMULUS AND EXERTION. 55 If the quiefcence of fibres, which had previoufly been fub- je<£t to perpetual ftimulus, coptinv.es a longer time, or their ac- cuftomed ftimulus be more completely withdrawn, the accu- mulation of fenforial power becomes ftill greater, as in thofe expofed to cold and hunger; pain is produced, and the organ gradually dies from the chemical changes which take place in It; or it is, at a great di fiance of time, reflored to addion by fti- mulus applied with great caution, in fmail quantity, as hap- pens to feme larger animals, and to many iniedts, which, dur- ing the winter months, lie benumbed with cold, and are laid to fleep, and to perfons apparently drowned, or apparently frozen to death. Snails have been faid to revive by throwing them into water, after having been many years fhut up in the cabi- nets of the curious ; and eggs and feeds in general, are reflored to life after many months of torpor by the ftimulus of warm water and moiflure. The inflammation of fthirrous tumours, which have long exifted in a flate of inaction, is a procels of this kind, as well as the fenfibility acquired by inflamed tendons and bones, which had, at their formation, a fimilar fenfibility, which had fo long lain dormant in their uninflamed (late. 3. If, after long quiefcence from defeCl of ftimulus, the fi- bres, which had previoufly been habituated to perpetual fti- muls, are again expofed to but their uiual quantity of it, as in thofe who have fuffered the extremes of cold or hunger, a violent exertion of the affeCled organ commences, owing, as above explained, to the great accumulation of fenforial power. This violent exertion not only diminifhes the accumulated fpi- lit of animation, but, at the fame time, induces pleafure or pain into the fyflem, w'hich, whether it be fucceeded by in- flammation or not, becomes an additional ftimulus, and adding along with the former one, produces ftill greater exertions, and thus reduces the fenforial power, in the contracting fibres, be- neath its natural quantity. When the fpirit of animation is thus exhaufted 'by ufelefs exertions, the organ becomes torpid, or unexcitable into aCticn, and a fecond fit of quiefcence fucceeds that of abundant acti- vity. During this fecond fit of quiefcence, the fenforial power becomes again accumulated, and another fit of exer- tion follows in train. Thefe viciffitudes of exertion and in- ertion of the arterial fyflem, conftitute the paroxyfms of re- mittent fevers ; or intermittent ones, when there is an interval of the natural aCtion of the arteries between the exacerbations. In thefe paroxyfms of fevers, which confift of the libration of the arterial lyilem, between the extremes of exertion and quiefcence, S 6 OF STIMULUS AND EXERTION. Sect. XII. 3. quiefcence, either the fits become lefs and lefs violent, from the contraftile fibres becoming lefs and lefs excitable to the fti- mulus by habit, that is, by becoming accuftomed to it, as ex- plained below, XII. 3. 1. or the whole fenforial power be- comes exhaufled, and the arteries ceafe to beat, and the patient dies in the cold part of the paroxyfm. Or, fecOndly, io much pain is introduced into the fyftem by the violent contractions of the fibres, that inflammation arifes, which prevents future cold fits, by expending a part of the fenforial power in the ex- tenfion of old veflcls or the production of new ones, and thus preventing the too great accumulation or exertion of ic in other parts of the fyftem ; or which, by the great increase eft ftimu- ■lus, excites into great action the whole glandular fyftem, as well as the arterial, and thence a greater quantity of fenforial power is produced in the brain, and thus its exhauftion in any peculiar part of the fyftem, ceafes to be affefted. 4. Or, thirdly, in confequence of the painful or pleafurable fenfation above mentioned, defire and averfion are introduced, and inordinate volition fucceeds ; which, by its own exertions, expends fo much of the fpirit of animation, that die two other fenforial faculties, or irritation and fenfation, aft fo much fee- bler, that the paroxyfms of fever, or that libration between the extremes of exertion and inaftivity of the arterial fyftem, gra- dually fublides. On this account a temporary infanity is a favourable fign in fevers, as I have had fome opportunities o 1 obferving. III. Of repeated Stimulus. 1. When a ftimulus is repeated more frequently than the expenditure of fenforial power can be renewed in the afting organ, the efteft of the ftimulus becomes gradually dimiuilli- ■ed. Thus, if two grains of opium be fvvallowed bv a perfon unufed to fo ftrong a ftimulus, all the vafcular fyftems in the body aft with greater energy ; all the fecretions and the abforp- tion from thofe fecreted fluids are in'ereafed in quantity ; and pleafure or pain are introduced into the fyftem, which adds an additional ftimulus to that already too great. After iome hours the fenforial power becomes di mini (bed in quantity, ex- pended by the great aftivity of the fyftem ; and thence, when the ftimulus of the opium is withdrawn, the fibres will not obey their ufual degree of natural ftimulus, and a confequent torpor or quiefcence fucceeds, as is experienced by drunkards, who, on the day after a great excels’ of fpirituous potation, feel indigeftion, head-ach, and general debility. In this fit of torpor or quiefcence of a part or of die whole of Sect. XII. 3. OF STIMULUS AND EXERTION. 57 of the fyftem, an accumulation of the fenlorial power in the affedfed hbres is formed, and occafions a fecond paroxvfm of exertion, by the application only of the natural ftimulus ; and thus a libration of the fenlorial exertion between one excels and the other, continues for two or three days, where the fti- mulus was violent in degree ; and for weeks in feme fevers, from the ftimulus of contagious matter. But if a fecond dofe of opium be exhibited before the fibres have regained their natural quantity of lenforial power, its ef- fect will be much lei's than the former, becaufe the fpirit of animation, or fenforial power, is in part exhaufted by the pre- vious excefs of exertion. Hence all medicines, repeated too frequently, gradually lofe their effedt, as opium and wine. Many things of difagreeable tafte at firft, ceafe to be difagree- ble by frequent repetition, as tobacco ; grief and pain gradually diminilh, and at length ceafe altogether and hence life itfelf becomes tolerable. Befides the temporary diminution of the fpirit of animation or fenforial power, which is naturally ftationary or refident in every living fibre, by a fingle exhibition of a powerful ftimulus, the contradlile fibres themfelves, by the perpetual application of a new quantity of ftimulus, before they have regained their natural quantity of fenforial power, appear to fuller in their capability of receiving fo much as the natural quantity of fen- forial power ; and hence a permanent deficiency of fpirit of ani- mation takes place, however long the ftimulus may have been withdrawn. On this caufe depends the permanent debility of thofe who have been addidfed to intoxication, the general weak- hefs of old age, and the natural debility or irritability of thofe who have pale fkins and large pupils of their eyes. There is a curious phenomenon belongs to this place, which has always appeared difficult of folution ; and that is, that opium or aloes may be exhibited in fmall doles at firft, and gradually increafed to very large ones, without producing ftupor or diarr- hoea. In this cafe, though the opium and aloes are given in fuch fmall dofes as not to produce intoxication or catharfis, yet they are exhibited in quantities fufficient, in fome degree, to exhauft the fenforial power, and hence a ftronger and a ftronger dofe is required; otherwife the medicine would icon ceafe to adt at all. On the contrary, if the opium or aloes be exhibited in a large dofe at firft, fo as to produce intoxication or diarrhcea, after a few repetitions the quantity of either of them may be diminifhed, and they will ftill produce this effedt For the more powerful ftimulus diffevers the pwgreffive catenations of animal 58 OF STIMULUS AND EXERTION. Sect. XII. 3. animal motions, defcribed in Seel. XVII. and introduces a new link between them; whence every repetition ftrengthens this new atTociation or catenation, and the ftimulus mav be gradually decreafed, or be nearly withdrawn, and yet the effect fhall continue, becaufe the fenforial power of affociation or catenation, being united with the ftimulus, increafes in energy with every 1'epetition of the catenated circle; and it is bv thele means that all the irritative affociations of motions are origi- nally produced. 2. When a ftimulus is repeated at fuch diftant intervals of time, that the natural quantity of fenforial power becomes completely reftored in the acting fibres, it wiil act with the fame energy as when firft applied. Hence tin ft who have lately accuftomed themfelves to large dofes of opium, by begin- ning with fmall ones, and gradually increafmg them, and re- peating them frequently, as mentioned in the preceding para- graph, if they intermit the ufe of it for a few days only, mu ft begin again with as fmall dofes as they took at firft; otherwife they will experience the inconveniences of intoxication. On this circumftance depend the conftant unfailing effects of the various kinds of ftimulus, which excite into action all the vafcular fvftemsjn the body ; the arterial, venous, ablorb- cnt, and glandular veftels, are brought into perpetual, unwea- ried action by the fluids, which are adapted to ftimulate them; but thefe have the fenforial power of affociation added to that of irritation, and even, in fome degree, that of fenfation, and even of volition, as wiil he fpoken of in their places ; and life itleif is thus carried on by the production of fenforial power being equal to its wafte or expenditure in the perpetual move- ment of the vafcular organization. O m „ 3. When a ftimulus is repeated at uniform intervals of time, with fuch diftances between them that the expenditure of fen- forial power in the acting fibres becomes completely renewed, the effect is produced with greater facility or energy. For the fenforial power of affociation is combined with the fenfo- rial power of irritation; or, in common language, the acquired habit affifts the power of die ftimulus. This circumftance not only obtains in the annual and diur- nal catenations of animal motions, explained in Sect. XXXVI. but in every lefs circle of actions or ideas, as in the burdien of a fong, or the iterations of a dance, and conftitutes the plea- fure we receive from repetition and imitation, as treated of in Sect. XXII. 2. 4. When a ftimuluihas been many times- repeated at uni- form intervals, fo as tPproduce the complete action of the or- Sect. XII. 3. OF STIMULUS AND EXERTION, 59 gan, it may then be gradually diminifhed, or totally with- drawn, and the adtion of the organ will continue ; for the fenforial power of affociation becomes united with that of ir-* ritation, and by frequent repetition becomes at length of fuffi- cient energy to carry on the new link in the circle of adtions, without the irritation which at firft introduced it, Hence, when the bark is given at ftated intervals for the cure of intermittent fevers, if fixty grains of it be given every three hours for the twenty-four hours preceding the expected parox- vfm, fo as to Simulate the defective pan of the fyftem into adtion, and by that means to prevent the torpor or quiefcence of the fibres, which conftitutes the cold fit ; much le.s than half the quantity, given before the time at which another pa- roxyfm of quiefcence would have taken place, will be luffi- cient to prevent it ; becaufe now the fenforial power, termed affociation, adts in a twofold manner. Find, in refpedl to the period of the catenation in which the cold fit was produced, which is now diffevered by the ftronger ftimulus of the firft dofes of the bark; and, fecondly, becaufe each dofe of bark being repeated at periodical times, has its effedl increafed by the fenforial faculty of affociation being combined with that of irritation. Now, when fixty grains of Peruvian bark are taken twice a day, fuppofe at ten o’clock and at fix, for a fortnight, the ir- ritation excited by this additional ftimulus becomes a part of the diurnal. circle of adfions, and will at length carry on the increafed action of the fyftem without the afliftance of the fti- mulus of the bark. On this theory the bitter medicines, cha- lybeates, and opiates in appropriated dofes, exhibited for a fortnight, give permanent ftrength to pale, feeble children, and other weak conftitutions. 5. When a defect of ftimulus, as of heat, recufs at certain diurnal intervals, which induces fome torpor, or quiefcence of a part of the fyftem, the diurnal catenation of adtions becomes difordered, and a new affociation with this link of torpid ac- tion is formed ; on the next period the quantity of quiefcence will be increafed, fuppofe the fame defedt of ftimulus to recur ; becaufe now the new affociation confpires with the defective irritation in introducing the torpid action of this part of the diurnal catenation. In this manner many fever-fits commence, where the patient is for fome days indifpoled at certain hours, before the cold paroxyl'm of fever is completely formed. See Sedt. XVII. 3. 3. on catenation of animal motions. 6. If a ftimulus, which at firft excited the affedted organ into fo great exertion as to produce feAjtion, be continued K for 60 OF STIMULUS AND EXERTION. Sect. XII. 4. for a certain time, it will ceafe to produce fenfation both then anu when repeated, though the irritative motions in confe- quence of it may continue or be re-excited. Many catenations of irritative motions were at firft Suc- ceeded by fenfation, as the apparent motions of objects when we walk" paft them, and probably the vital motions themfeives in the early ftate of our exiftence. But as thofe fenfations were followed by no movements of the fyflem in confequence of them, they gradually ceafed to be produced, not being join- ed to any fucceeding link of catenation. Hence contagious matter, which has for feme weeks (Emulated the fyftem into great and permanent fenfation, ceafes afterwards to produce general fenfation, or inflammation, though it may ftiii induce topical irritations. See Sett. XXXIII. 2. 8. XIX. 10. Our abi’orbent fyftem then feems to receive thofe contagious matters, which it has before experienced, in the fame manner as it imbibes common moifture, or other fluids ; that is. with- out being thrown into fo violent adlion as to produce fenfa- tion ; the confequence of which is an increafe of daily energy or activity, til! inflammation and its confequences fucceed. 7. If a ftimulus excites an organ into fuch violent contrac- tions as to produce fenfation, tire motions of which organ had not ufually produced fenfation, this new fenforial power, added to the irritation occalioned by the ftimuius, increafes the acti- vity of the organ. And if this activity be catenated with the diurnal circle of aCtions, an increaftng inflammation is produc- ed, as in the evening paroxyfms of imali-pox, and other fevers with inflammation: and hence fchirrous tumours, tendons, and membranes, and probably the arteries themielves, become in- flamed, when they are ftrongly ftimulated. IV. Of Stimulus greater than natural. 1. A quantity of ftimulus greater than natural, producing an increafed exertion of fenforial power, whether that exertion be in the mode of irritation, fenfation, volition, or affociation, dim: a: mas the general quantity of it. This facl is obfervable in the pfogrefs of intoxication, as the increafed quantity or energy of the iri ita live motions, owing to the ftimulus of vi- nous ipifit, introduces much pleafurable fenfation into the fyf- tem, and much exertion of mufcular or fenfual motions in con- fequence of this increafed fenfation , the voluntary motions, and even the affociate ones, become much impaired or dimi- nilhed, anu delirium and {daggering fucceed. See Sedl. XXI. on drunkennefs. And hence the great proftration of the ftrengdr of the locoaflfcve ihufcles in fome fevers, is owing to * ' the Sect. XII. 4- OF STIMULUS AND EXERTION. 61 the exhauftion of fenforial power, by the increafed action of the arterial fyflem. In like manner a ftimulus greater than natural, applied to a part of the fyftem, increafes the exertion of tentorial power in that part, and diminifhes it in fome other part. As in the commencement of fcarlet fever, it is ufual to iee great rednefs and heat on the laces and breafts of children, while, at the fame time, their feet are colder than natural ; partial heats are obferv- able in other fevers with debility, and are generally attended with torpor, or quiefcence of fome other part of the fyftem. But thefe partial exertions of fenforial power are fometimes attended with increafed partial exertions in other parts of the fyftem, which fympathize with them, as the flufhing of tire lace after a full meal. But thefe, therefore, are to be afcrib'ed to fympathetic affociations, explained in Seel, XXXV. and not to general exhauftion. or accumulation of leniorial power. 2. A quantity of ftimulus greater than natural, producing an increafed exertion of fenforial power in any particular or- gan, diminifhes the quantity of it in that organ. This appears from the contradlions of animal fibres being not fo eafily excit- ed by a left; ftimulus, after the organ has been fubjecled to a greater. Thus, after.! looking at any luminous objedt of a fmall lize, as at the fetting fun for a fhort time, fo as not much to fatigue the eye, this part of the retina becomes lefs fenftble to fmaller quantities of light: hence, when- the eyes are turned on other lefs luminous parts Gf the Iky, a dark fpot is feen re- lembling the fhape of the fun, or other luminous object which we laft: beheld. 'See Sedt. XL. No. 2. Thus we are fome time before we can diftinguifti objedts in an obfeure room after coming from bright day-light, though the iris prefently contradls itlelfl We are not able to hear weak founds after loud ones. And the ftomachs of thofe who have been much habituated to the ftronger ftimulus of ferment- ed or fpirituous liquors, are not excited into due adiion by weaker ones. 3. A quantity of ftimulus fomething greater than the laft mentioned, or longer continued, induces the organ into fpaf- medic adiion, which ceales and recurs alternately. Thus, on looking for a time on the fetting fun, fo as not greatly to fatigue the light, a yellow fpedfrum is feen when the eyes are clofed and covered, which continues for a time, and then diiappears and recurs repeatedly before it entirely vaniflres. See Sedl- XL. No. 5. Thus the adiion of vomiting ceafes and is re- newed by intervals, although the err^^ drug is thrown up with tire firft etrort,. A tenefmus cc^Jfcucs by intervals fome time 62 OF STIMULUS AND EXERTION. Sect. XII. 4. time after the exclufion of acrid excrement; and the pulfations • of the heart of a viper are faid to continue l'ome time after it ft cleared from its blood. In thefe cafes, the violent contradlions of the fibres produce pain, according to law 4; and this pain conffcirutes an additional kind or quantity of excitement, which again induces the fi- bres into contraction ; and which painful excitement is again renewed, and again induces contractions of the fibres with gra- dually diminifhing effed:. 4. A quantity of ftimulus greater than that lad mentioned, or longer continued, induces the antagonift mufcles into fpaf- xnodic addon. This is beautifully illuftrated by the ocular fpedra, defcribed in Sed. XL. No. 6, to which the reader is referred. From thefe experiments there is reafon to conclude, that the fatigued part of the retina throws itfelf into a contrary mode of adion, like ofeitation or pandiculation, as foon as the ftimulus, which has fatigued it; is withdrawn ; but that it ftill remains liable to be excited into adion bv anv ether colours except the colour with which it has been fatigued. Thus the yawning and ftretching the limbs after a continued adiion or attitude, feems occafioned by the antagonift mufcles being fti- mulated by their extenfton during the contractions of thofe in adion, or in the fituation in which that adion left left them. 5. A quantity of ftimulus greater than the laft, or longer continued, induces variety of convulfions 01 fixed ipafms, ei- ther of the aff'eded organ, or of the moving fibres in other parts ' of the bodv. In refped: to the fpedra in the eye,. this is well illuftrated in No. 7 and 8 of Sect. XL. Epileptic convul- fions, as the emprofthotonos and opifthotonos, with the cramp of the calf of the leg, locked jaw, and other cataleptic fits, ap- pear to orignate from pain, as fome of thefe patients feream aloud before the convulfion takes place ; which ieems at firft to be an effort to relieve painful fenfation, and afterwards an effort to prevent it. In thefe cafes the violent contradions of the fibres produce fo much pain, as to conftitute a perpetual excitement ; and that in fo great degree, as to allow but fmall intervals of relaxation of the contrading fibres, as in convulfions; or no interval^at all, as in fixed fpafms. ’ 6. A quantity of ftimulus greater than the laft, or longer continued, produces a paralyiis of the organ. In many caies this paralyfis is only a temporary effed, as on looking long cn a fmall aera of bright red filk, placed cn a fheet of white pa- per on the floor in a ft^ig light, the red fill: gradually becomes paler, and at length ^■p , ' C Y.r> which evinces that a part of • the Sect. XII. 5. OF STIMULUS AND EXERTION. 63 the retina, by being violently excited, becomes for a time un- affected by the famulus of that colour. Thus, cathartic me- dicines, opiates, poifons, contagious matter, ceafe to influence our fy idem, after it has been habituated to the ufe of them, ex-, cept by the exhibition of inereafed quantities ot them ; our fi- bres not only become unaffected by famuli, by which they have previouflv been violently irritated, as by the matter of the finall- pox or meafles ; but they alio become unaffected by ienfation, where the violent exertions, which difabled them, were in coniequence of too great quantity of fenfation. And, laftly, the fibres, which become difobedient to volition, are probably difabled by their too violent exertions, in confequence of too great a quantity of volition. After every exertion of our fibres, a temporary paralyfis fucceeds, whence intervals of all mufcular contractions, as mentioned in No. 3 and 4 of this Section : the immediate cauie of thefemore permanent kinds of par aly fiscs probably owing, in the fame manner, to the too great exhauftion of the fpirit of animation in the affected part ; fo that a ftronger ftimulus is required, or one of a different kind from that which occafion- ed thofe'two violent contractions, to again excite the affected organ into activity ; and if a ftronger ftimulus could be appli- ed, it muff again induce paralyfis. For thefe powerful ftimuli .excite pain at the fame time that they produce irritation ; and this pain not only excites fibrous motions by its ftimulus, but it alio produces volition; and thus all thefe ftimuli acting at the fame time, and fometimes with ‘ the addition of their affociations, produce fo great exertion as to expend the whole of the feniorial power in the affected fibres. - -> V. Of Stimulus lefs than natural. x. A quantity of ftimulus lefs than natural, producing a decreafed exertion of fenforial power, occafions an accumula- tion of ic. This circumftance is obfervable in the haemipla- gia, in which the patients are perpetually moving the muffles which are unaffected. On this account we awake with greater vigour after deep,' becaufe, during fo many hours, the great ufual expenditure of fenforial porter in the performance of vo- luntary actions, and in the exertions of our organs ot fenfe, in coniequence of the irritations occafionedbv external objedts, had been fufpended, and a cenfequent accumulation had taken place. In like manner the exertion of the faaforial power lefs than natural in one pah of the fyftem, is liatiJPo produce an increafe of 6 4 OF STIMULUS AND EXERTION. Sect. XII. s . of the exertion of it in fome other part. Thus, bv the action of vomiting, in which the natural exertion of the motions of the flomach are deftroyed or diminifhed, an increafed ubforp- tion of the pulmonary and cellular lymphatics is produced, as is known by the increafed abforption of the fluid depofited in them in dropfical cafes. But thefe partial quiefcences of fen - forial power, are alfo fometimes attended with other partial quiefcences,- which fympathize with them, as cold and pale ex- tremities from hunger. Thefe, therefore, are to be afcribed to the afTociations of fympathy. explained in Seel. XXXV. and not to the general accumulation of fenforial power. 2. A quantity of ftimulus lefs than natural, applied to fibres nrevioufty accuftomed to perpetual ftimulus, is fucceeacd by accumulation of fenforial power in the affected organ. The truth of this proportion is evinced, becaufe a ftimulus lefs than natural, if it be fomewhat greater than that above men- tioned, will excite the organ fo circumftanced into violent ac- tivity. Thus, or, a trolly day with wind, the face of a perfen expofed to the wind is at fir ft pale and fhrunk ; but on turning the face from the wind, it becomesToon of a glow with warmth and fiufhing. The glow of the ft; in in emerging from the cold-bath, is owing to the fame caufe. It does not appear that an accumulation of fenforial power above the natural quantity, is acquired by thofe mufclcs v/mch ■are not fubjeft to perpetual ftimulus, as the locomotive muf- -cles : thefe, after the greateft fatigue, only acquire by reft their ufual aptitude to motion ; whereas the vafeuiar fyftem, as the heart and arteries, after a fhort quiefcence, are thrown into violent adlion by their natural quantity of ftimulus. Neverthelefs, by this accumulation of fenforial power during the application of dccreafed ftimulus, and by the exhau! or. of it during the ariiion of increafed ftimulus, it is wifely pro- vided, that the adlions of the vafeuiar mufcles and organs of fenfe are not much deranged by fmall variations of ftimulus; as the quantity of fenforial power becomes, in fome meaiure, inverfely as the quantity of ftimulus. 3. A quantity of ftimulus lefs than that mentioned above, and continued for fome time, induces pain in the affetfted or- gan ; as the pain of cold in the hands, when they are immerfed in fnow, is owing to a deficiency of the ftimulation of heat. Hunger is a pain from the deficiency of the ftimulation of food. Pain in the back at the commencement of ague-firs, and the Iiead-achs which attend feeble people, are pains from defect of ftimulus, and araJieiice' relieved by opium, efientiai oils, and lpirit of wine, As SfcT.XII. 5. OF STIMULUS AND EXERTION. 65 As the pains which originate from defedt of ftimulus only occur in thoie parts of the fyftem which have been previouny iubjedted to perpetual ftimulus ; and as an accumulation of feniorial power is produced in the quiefcent organ along with the pain, as in cold or hunger, there is reafon to believe, that the pain is owing to the accumulation of fenforial power. For, in the locomotive lmifcles,' in the retina of the eye, and other organs of fenfes, no pain occurs from the abfence of fti- mulus, nor any great accumulation of fenforial power beyond their natural quantity, ftnce thele organs have not been ufed to a perpetual fupply of it. There is, indeed, a greater accurnu - lation occurs in the organ of vifton after its quiefcence, becauie it is fubjedt to more conftant ftimulus. 4. A certain quantity of ftimulus lefs than natural, induces the moving organ into feebler and more frequent contractions, as mentioned in No. I. 4. of this Sedtion. For' each contrac- tion moving through a lefs fpace, or with lefs force, that is, with lefs expenditure of the fpirit of animation, is fooner relax- ed, and the ipirit of animation, derived at each interval into the adting fibres, being lefs, thefe intervals likewife become fhorter. Hence the tremours of the hands of people accuftomed to vinous fpirit, till they take their ufual ftimulus ; hence the quick pulfe in fevers attended with debility, which is greater than in fevers attended with firength ; in the latter, the pulfe feldom beats above 120 times in a minute, in the former it fre- quently exceeds 140. It mull; be obferved, that in this and the two following arti- cles, the decreafed adiion of the fyftem is probably more fre- quently occafioned by deficiency in the quantity of fenforial power, than in the quantity of ftimulus. Thus thofe feeble confti utions which have large pupils of their eyes, and all who labour under nervous fevers, feem to owe their want of natural quantity of adiivity in the fyftem, to the deficiency of fenforial power ; fince, as far as can be feen, they frequently poflefs the natural quantity of ftimulus. 5. A certain quantity of ftimulus, lefs than that above men- tioned, inverts the order of fucceffive fibrous contractions ; as in vomiting, the vermicular motions of the ftomach and duo- denum are inverted, and their contents ejedted ; which is pro- bably owing to the exhauftion of the fpirit of animation in the adling mufeies, by a previous exceffive ftimulus, as by the root of ipecacuanha, and the confequent defedt: of fenfoiial power. The fame retrogade motions affect the whole inteftinal canal in ileus ; and the ceiophagus, in globus hyftericus. See this farther explained in Sedt. XXIX, No.lflfe, on Retrogade Mo- tions. I muft 66 OF STIMULUS AND EXERTION. Sect. XII. 6. I muft: ofcferve, alio, that fcmethirig fimilar happens in the produdtionof our ideas, oi fenfual motions, when they are too weakly excited : when any one is thinking intenfely about one thing, and carelefsly converting about- another, he is liable to ufe the word of a contrary meaning to that which he defined., as cold weather for hot weather, fummer for winter. 6. A certain quantity of flimulus, lei's than that above men tioned, is fucceeded byparalyfis, firft of the voluntary and fen- fitive motions, and afterwards of thcfe of irritation and of aflociation, which conftitute death. VI. Cure of iricreafcd exertion. i. The cure which nature has provided for the increased exertion of any part of the fyftem, coniifts in the confequent expenditure of the feniorial power. But as a greater torpor follows this exhauftion ot fenforial power, as explained in the next paragraph, and a greater exertion fucceeds this torpor, the conftitution frequently links under thefe increahng libra- tions, between exertion and quiefcence, till at length complete qmefcence, that is, death, doles the fcene. For, during the great exertion of the fyftem in the hot fit of fever, an increafe of ftimulus is produced from the greater mo- mentum of the blood, the greater diftention of the heart and arteries, and die increafed produdiion of heat, by the violent adtions of the fyftem, occaiioned by this augmentation of fti- mulus ; the fenforial power becomes diminilhed in a few hours much beneath its natural quantity, the veflels at length ceui'e to obey even thefe great degrees of ftimulus, as fhewn :n Sech XL. g. l . and a torpor of the whole or of a part of the fyftem enfues. Now, as this fecond cold fit commences with a greater de- ficiency of fenforial power, it is alfo attended wi a greater deficiency of ftimulus than in the preceding cold fit , that is, wdth lefs momentum of blood, lefs diftention of the heart. On this account the fecond cold fit becomes more violent and ot longer duration than the firft ; and as a greater accumulation of fenforial power muft be produced before the fyftem or vef- fels will again obey the diminilhed ftimulus, it follows, dial the fecond not fit of fever will be more violent than the former one : and that unlefs fome other caufes counteract either the violent exertions in the hot fit, or the great torpor in the cold fit, life will at length be extinguifhed, by the expenditure of die whole of the fenforial power. And from hence it appears, that the true means qf^uring fevers muft be iuch as decrease the ahhon of the fyft® in the hot fit, and increafe it in the cold Ssct. XII. 7. OF STIMULUS AND EXERTION. 67 cold fit; that is, fuch as prevent the too great diminution of fenforial power in the hot fit, and the too great accumulation of it in the cold one. 2. Where the exertion of the fenforial powers is much in- creafed, as in the hot fits of fever or inflammation, the follow- ing are the ufual means of relieving it. Decreafe the irrita- tions by blood-letting, and other evacuations ; by cold water taken into the ftomach, or injedted as enema, or ufed external- ly ; by cold air breathed into the lungs, and diffufed over the fkin ; with food of lefs ftimulus than the patient has been ac- cuftomed to. 3. As a cold fir, or paroxyfm of inactivity of fome parts of the fyftem, generally precedes the hot fit, or paroxyfm of exertion, by which the fenforial power becomes accumulated ; this cold paroxyfm fhould be prevented by ftimulant medicines and diet, as wine, opium, bark, warmth, cheerfulnefs, anger, furprife. 4. Excite into greater adtion fome other part of the fyf- tem, by which means the fpirit of animation may be in part expended, and thence the inordinate adb'ons of the difeafed part may be leffened. Hence, when a part of the fkin adls violently, as of the face in the eruption of the finall-pox, if the feet be cold they fhould be covered. Hence the ufe of a blifter applied near a topical inflammation. Hence opium and warm bada relieve pains both from excels and defedt of ftimulus. 5. Firffc increafe the general ftimulation above its natural quantity, which may in fome degree exhauft the fpirit of ani- mation; and then decreafe the ftimulation beneath its natural quantity. Hence, after fudorific medicines and warm air, the application of refrigerants may have greater effect, if they could be adminiflered without danger of producing too great torpor of fome part of the fyftem ; as frequently happens to people in health from coming out of a warm room into the cold air, by which a topical inflammation, in confequence of torpor of the mucous membrane of the noftril, is produced, and is termed a cold in the head. VII. Cure of decreafed Exertion. 1. Where the exertion of the fenforial powers is much decreafed, as in the cold fits of fever, a gradual accumulation of the fpirit of animation takes place; as occurs in all cafes where inactivity or torpor of a part of the fyftem exifts ; this accumulation of fenforial power increafes, till ftimuli lefs than natural are fufficient to throw it*urto action, then the L cold 68 OF STIMULUS AND EXERTION. Sect. XII. 7. cold fit ceafes ; and, from the action of the natural .ftimuli, a hot one fucceeds with incieafed activity of the whole fyftem. So, in fainting fits, or fyneope, there is a temporary deficien- cy of fenforial exertions, and a confequent quiefcence of a great part of the fyftem. This quiefcence continues, till the fenforial power becomes again accumulated in the torpid or- gans ; and then the ufual diurnal ftimuli excite the revivefcent parts again into action; but as this kind of quiefcence conti- nues hut a (hort time compared to the cold paroxyfm of an ague, and lefs affefts the circulatory fyftem, a lefs fuperabun- dency of exertion fucceeds in the organs previoufty torpid, and a lefs excefs of arterial activity. See Se6t. XXXIV. 1. 6. 2. In the difeales occafioned by a defedt of fenforial exer- tion, as in cold fits of ague, hyfteric complaint, and nervous fever, the following means are thole commonly ufed. 1. In- creafe the ftimulation above its natural quantity forfome weeks, till a new habit of more energetic contraction of the fibres is eftablifhed. This is to be done by wine, opium, bar k, fteel, given at exadt periods, and in appropriate quantities lor j:' thefe medicines be given in inch quantity as to induce the leaft degree of intoxication, a debility fucceeds from the ufe! efs ex- hauftion of fpirit of animation, in eonfequence of too grea r exertion of the mufcles, or organs of fenfe. To thefe irrita- tive ftimuli fhould be added the fenlitive ones of cheerful ide hope, attention. 3. Change the kind of ftimulus. The habits acquired bv the conftitution depend on fuch nice circumftanees, that when one kind of ftimulus ceafes to excite the fenforial power inm tire quantity of exertion neceflary to health, it is often iuffici- ent to change the ftimulus for another apparently fimiiar in quantity and quality. Thus, when wine ceafes to ftimulatu the conftitution, opium, in appropriate doles, i'upplies the de- fedt; and the contrary. This is all'o obferved in the eftedl- of cathartic medicines ; when one lofes its power, another, ap- parently lefs efficacious, will fuccc-ed. Hence a change of diet, drink, and ftimulating medicines, is often advantageous in difeafes of debility. 4. Stimulate the organs, whofe motions are aftociated with the torpid parts of the fyftem. The adtions of die minute vel- fels of the various parts of the external fkin, are not onh ;i (lo- ci a ted with each other, but are ftronglv aftociated with thole of fome ot the internal membranes, and particularly or the ftomach'. Hence, when the exertion ol the ftomath is lets than natural, and indigeftion and heait-burn fucceed, nothing fo certainly removetyffiefe fvmptoivn. as the ftimulus ot a b! Sect. XII.7. OF STIMULUS AND EXERTION. 69 ter on the back. The coldnefs of the extremities, as of the nofe, ears, or lingers, are hence the bell indication for the fuc- cefsful application of bidders'. r. Decreafe the ftimulus for a time. By leflening tb.e quan- tity of heat for 2 minute or two, by going into the cold bath, a great accumulation of fenforial power is produced; for, not only the minute veffels of the whole external fkin, for a time become inadiive, as appears by their palenefs, but the minute veffels of the lungs lofe much of their adhVity alfo, by concert with thofe of the fkin, as appears from the difficulty of breath- ing at ffrft going into cold water. On emerging from the bath, the fenforial power is thrown into great exertion by the ftimu- lus of tire common degree of the warmth of the atmol'phere, and a great production of animal heat is the confequence. The longer a perfon continues in the cold bath, the greater muff be the prefent inertion of a great part of the fyftem, and so confequence, a greater accumulation of fenforial power. Whence M. Pome recommends lome melancholy patients to be kept from two to fix hours in fpring-water, and m baths jftill colder. -6. Decreafe the ftimulus for a time below the natural, and then increafe it above natural. The effedf of this procefs, improperly ufed, is feen in giving much food, or applying much warmth, to thofe who have been previoufly expofed to great hunger, or to great cold. The accumulated fenforial power is thrown into fo violent exertion, that inflammations and mortifications fupervene, and death clofes the cataftrophe. In many difeafes this method is the moll fuccefsful ; hence the hark in agues produces more certain effedl alter the previous exhibition of emetics. In difeafes attended with violent pain, opium lias double the effecSt, if venefedtlon and a cathartic have been previoufly ufcJ. On this feems to have been founded the fuccefsful practice of Sydenham, who ufed venefcdlion and a cathartic in choloriffs, before the exhibition of the bark, fteel, and opiates. 7. Prevent any unneceflary expenditure of fenforial power Hence, in levers with debility, a decumbent poflure is prefer- red, with filenee, little light, and fuch a quantity of heat as may prevent any chill lenfation, or any coldnefs ot the extremities. The pulfe of patients in fevers with debility, increases in fre- quency above ten pulfations in a minute 011 their riling out of bed. For the expenditure of fenforial power to prelerve an credl pofture of the body, adds to the general deficiency of it, and thus affefts the circulation. S. The longer in time, and the greater in degree, the quie- l lcence jo OF STIMULUS AND EXERTION. Sect. XII.-. lienee or inertion of an organ has been, fo that it ftill retains life or excitability, the lefs ftimulus fliould at firft be applied to it. The quantity of {Emulation is a matter of great nicetv to determine, where the torpor or quiefcence of the fibres has been experienced in a great degree, or for a conliderable time, as in cold fits of the ague, in continued fevers with great debi lity, or in people famifhed at lea, or peri filing with cold. In the two laft cafes, very minute quantities of food fiiould be firft {applied, and very few additional degrees of heat. In die two former cafes, but little ftimulus ot wine or medicine, above what they had been lately accuftomed to, fliould be exhibited, and this at frequent and ftated intervals, fo that the effect ot one quantity may be obferved before the exhibition of anodier. It thefe circa mftances are not attended to, as the fenforial power ^becomes accumulated in the quiefeent fibres, an inor- dinate exertion takes place, by the increafe of ftimulus adding on the accumulated quantity of fenforial power, and either the paralyfis, or death of the contradtile fibres enfues, from die to- tal expenditure of the fenforial purs er in the affected organ, owing to this increafe of exertion, like the debility after intox- ication. Or, fecondly, the violent exertions above mentioned, produce painful fenfation, which becomes a new ftimulus, and by thus producing inflammation, and increafing the adtivitv of the fibres already too great, fooncr exhaufts the whole ot the fenforial power in die acting organ, and mortification ; diat is, the death of the part, fupervenes. Hence there have been many inftances of people, whofe limbs have been long benumbed bv expofure to cold, who have loft them by mortification, on their being too liu'tily brought to the fire ; and of others, who were nearly famished at fea, who have died foon after having taken not more than an ufual meal of food. I have iieard of two well attefted inftances of pa- tients, in the cold fit of ague, who have died horn the exltibi- tion of gin and vinegar, by die inflammation which enfued. And in many fevers attended with debility, the unlimited ufe of wine, and the wanton application ot blifters, I believe, have de- ftroyed numbers, by the debility confequent to too great {Emu- lation ; that is, by the exhauftion of the fenforial power by its inordinate exertion. Wherever the lea ft degree of intoxication cxifts, a propor- tional debility is the confequence ; but there is a golden rule, bv which the neceffary and ufeful quantity of ftimulus, in fevers with debility, may be afeertained. When wine or beer are exhibited, either alone, or diluted with water, it the piffle be- comes flower, the ftimulus is of a .proper quantity, and lliould Sect. XIII. i. OF VEGETABLE ANIMATION. 71 . be repeated every two or three hours, or when the pulfe again becomes quicker. In the chronical debility, brought on by drinking fpiiituous or fermented hquors, there is another golden rule, by which I have fi’ccefsfully directed the quantity of fpirit which they may lately ieffen, for there is no other means by which they can re- cover their health. It fhould be prernifed, that, where the power ofdigeftion in thefe patients is totally deftroyed, there is not much rcalon to expedt a return to healthful vigour. I nave diredted feveral of thefe patients to omit one fourth part of the quantity of vinous fpirits they -have been lately ac- cuflomed to ; and if in a fortnight their appetite increafes, they are advifed to omit another fourth part ; but it they perceive that them digeftion becomes impaired ter the want cl this quan- tity of fpirituous potation, they are advifed to continue as they are, and rather bear the ills they have, than ritk the encounter of greater. At the fame time, fiefh-meat, with or without fpice, is recommended, with Peruvian bark, and Heel, in frr.all quan- tities, between their meals, and half a grain of opium, or a grain, with live or eight grains of rhubarb at night. SECT. XIII. OF VEGETABLE ANIMATION. I. 1. Vegetables are irritable , mimofa, dioneea mufcipula. Vegetable fecretions. 2. Vegetable buds are inferior ani- mals , 1 arc liable to greater or lefs irritability. II. Sta- mens and pijtils of plants Jheiu marks of fenjibihty. III. Vegetables pojfefs Jome degree of volition. IV. Motions of plants are'aJJb'ciated like thojc of animals. V. 1. Ve- getable fr allure like that of animals, their anthers and fiigmas arc living creatures. Male-flowers of Vallijne- ria. 2 . Whether vegetables pojfefs ideas ? They have organs of fenfe, as of touch and Jmell, and ideas of exter- nal thin" s. o I. 1. TKE fibres of the vegetable world, as well as thole of the animal, are excitable into a variety ot motion by the ir- ritations of external obj eels. This appears particularly in the mimoia or fenfitive plant, whofeleay.es contrail on the fiighteft injury: the diontea mufcipula, which was lately brought ever from the marines of America, prefents us with another curi- ous milance. ct vegetable irritability; its leaves are armed with fpincs 72 OF VEGETABLE ANIMATION. Sect. XIII. r. fpinc-s on their upper edge, and are fpread on the ground around their Item; when an infecft creeps on any of the.n in its paf- fage to the flower or feed, the leaf flruts upli'.e a flee', rat-trap, and deflroys its enemy. See Botanic Garden, Parr JI. note on Siiene. The various Accretions of vegetables, as ,of odours, fruit, gum, refin, wax, honey, feem brought about in tire faux man- ner as in the glands of animals : the tafteiefs moifiure of the earth is converted by the hop-plant, into a bitter juice • as by the caterpillar in the nut-flheil, the fweet kernel is converted into a bitter powder. While the powder of ablorption in the roots and barks of vegetables, is excited into adlion bv the flu- ids applied to their mouths, like the lacleals and lympatics of animals. 2. The individuals of the vegetable world may be conlidered as inferior or lefs perfedf animals ; a tree is a congeries of many living buds, and in this refpedf refembles the branches of coral- line, which are a congeries of a multitude of animals. Each of thefe buds of a tree Iras its proper leaves or petals for lungs, produces its viviparous or its oviparous offspring in buds or feeds; has its own roots, which, extending down tire Hem of the tree, are interwoven with the roots of the other buds, and form the bark, which is the only living part of the Item, is annually renewed, and is lnperinduced upon the former baill, which then dies, and, with its ftagnated juices graduallv har- dening into -wood, forms the concentric circles which we fey in blocks of timber. The following circumftances evince the individuality of the buds of trees. Find, there are many trees whole whole internal wood is perifhed, and j et tire branches are vegete and healthy. Secondly, the fibres of the barks of trees are chiefly longitudi- nal, refenrbiing roots, as is beautifullj r ieen in thofe prepared bat ks that were lately brought from Otaheita. Thirdly, in ho- rizontal wounds of tire bark of trees, the fibres of the upper lip are always elongated downwards like roots, but thole of the lower lip do not approach to meet them. Fourthly, if you wrap wet nrofs round any joint of a vine, or cover it with moift earth, roots will flroot out from it. Fifthly, by the inoculation or engrafting of trees, many fruits are produced from one ftem. Sixthly, a new tree is produced from a branch plucked from an old one, and let in the ground. Whence it appears, that the buds of deciduous trees are l'o many annual plants; that the bark i? a contexture of the roots of each individual bud; and that tiie internal wood is of no other ufc but to l'upport them in the air; and that thus they refemble the animal world in their individuality. The h ^ /•> Sect. XIII. 4. OF VEGETAELE ANIMATION. The irritability of plants, like that oi animals, appears li- able to be increafed or decreased by habit; tor thole trees or throbs, which are brought from a colder climate to awarmei, put on their leaves and blofloms a fortnight fooner than the indigenous ones. Profeffor Kalin, in his travels in New- York, obferves, that the apple-trees brought from England, bloflorm a fortnight fooner than native ones. In cur country, the flmibs that are brought a decree or uvo from the north, are obierved to flou- i iih better titan thofe which come from tite fouth. The Sibe- rian barley and cabbage are faid to grow larger in this climate,, than the fimiiar more ibuthern vegetables. And our hoards of roots, as of potatoes and onions, germinate with lefs heat in j'pnng, after they have been accuftomed to the winter’s cold, than in autumn, after the fummer’s heat. 11 The ftamens and piftils of flowers fhew evident marks of feniibiiity, not only from many of the ftamens and force piftils approaching to each other at thefeafon cl impregnation, but from many of them clofing their petals and calyxes during the bold parts of the day. For this cannot be aferibed to irri- tation, becaufe cold means a deleft of the Hamulus of heat : but, as. the want of accuftomed ftimuli produces pain, as in coldnefs, hunger, and thirft of animals, thefe motions cf vege- tables, in doling up their flowers, muft be aferibed to thedifa- greeable fenfation, and not to the irritation of cold. Others clofe up their leaves during darknefs, which, like tire former, cannot he owing to irritation, as the irritating material is withdrawn. The approach of the anthers in many flowers to the flag- mas , and of the piftils of fome flowers to the anthers, muft be aferibed to the paffion of love, and hence belongs to fenfation, not to irritation. III. That the vegetable world pouches fome degree of vo- luntary powers, appears from their neceffity to fieep, which we have {hewn, in Sect. XVIII. to eonhft in tire temporary aboli - tion of voluntary power. This voluntary power feems to be exerted in the circular movement ot the tendrils of vines, and other climbing vegetables; or in the efforts to turn the upper furface ot their leaves, or their fhowers-to the light. IV. The alfociations of fibrous motions are obfervable in the vegetable world, as well as in the animal. The demons of the leaves of the feniitive plant have been accuftomed to con- tra ft at the lame time from the abfence of lftht ; hence, if by any other circumftance, a.s a flight ftroke 01 injury, one diviV lion is irritated into contraction, tire neighbouring ones con- traft u OF VEGETABLE ANIMATION. Sect. XIII. c. traff alfo, from their motions being affociated with thofe of the irritated part. So the various ftamina of the clafs o fyn - genefia have been accuftomed to contract together in the even- ing, and thence, it you ftimulate one of them with a pin, ac- cording to the experiment of M. Colvolo, they all contract from their acquired aflfoekrtions. Jo evince that the collapfmg of the fenfitive plant is no: owing to any mechanical vibrations propagated along the whole branch, when a fingle leaf is ftrucJCwith the linger, a leaf of it was ftit with {harp feiffors, and fome feconds of time palled before the plant feemed fenfible of the injury; and then the whole branch collapfed as far as the principal Item. This ex- periment was repeated feveral times with tire leaft poflmle im- pulfe to the plant. V. x. For the numerous circumftances in which vegeta- ble buds are analogous to animals, the reader is referred to the additional notes at the end of the Botanic Garden, Part I. I? is there (hewn, that the roots of vegetables referable the lac- teal fyflem of animals; the fap-veflels in the early fpring, be- fore their leaves expand, are analogous to the placenta! velfels ot the Icetus ; that the leaves of land-plants rcfemble lungs, and thofe of aquatic plants the gills of fifh ; diet there are other fyftetns of velfels refembling the vena portarum of quadrupeds, or the aorta of hlh ; that the digeflive power of vegetables is fimilar to that of animals converting the fluids, which drey abforb into fugar ; that their feeds referable tire- eggs of animals, and their buds and bulbs their viviparous cff- ipring. Atrd, laftly, that the anthers and itigmas are real animals, attached, indeed, to their parent tree, like polypi or coral infefts, but capable of fpantaneuus motion ; that they are a tie fled with the paffion of love, and furniflied with powers of re-producing their fpecies, and are fed with honey like the moths and butterflies, which plunder their nectaries. See Botanic Garden, Part I. add. note XXXIX. The male flowers of vallifneria approach Hill nearer to apparent animality, as they detach themfeives from the parent plant, and float on the furtace of the water to the female ones. Botanic Garden, Part II. art. Vailifnerki. Other flowers, of the clafles of monecia anddtecia, and polvgamia, difeharge the fecundating ferina, which, floating in die air, ;s carried to the flignru of the female flowers, and that at coniiderable diflances. Can this be affected by any fpeciflc attraction? or. like the diffuuon of the odorous particles ot flowers, is it left to the currents of winds, and the accidental mifear-riages of ic coun- teracted bv the quantity of its production ? 2. This Sect. XIII. 5. OF VEGETABLE ANIMATION. 7 s 2. This leads us to a curious enquiry, whether vegetables have ideas of external things ? As all our ideas are originally- received by our fenfes, the queftion may be changed to, whe- ther vegetables poffefs any organs of feme ? Certain it is, that they poffefs a fenfe of heat and cold, another of moifture and drynefs, and another of light and darknefs ; ' for they clofe their petals occalionally from the prefence of cold, moifture, or darknefs. And it has been already fhewn, that thefe actions cannot be performed limply from irritation, becaufe cold and darknefs are negative quantities, and on that account fenfation or volition are implied, and, in confequence, a fenforium or union of their nerves. So when we go into the light, we contrail the iris ; not from any ftimulus of the light on the fine mufcles of the iris, but from its motions being affociated with the fenfation of too much light on the retina, which could not take place without a fenforium or centre of union of the nerves of the iris with thofe of vilion. See Botanic Garden, Part I. Canto 3. 1 . 440, note. Belides thefe organs of fenfe, which diflinguifh cold, moif- ture, and darknefs, the leaves of mimofa, and of dionaea, and of drolera, and the ftamens of many flowers, as of the berber- ry, and the numerous clafs of fyngenefla, are fenfible to me- chanic impait ; that is, they poffefs a fenfe of touch, as well as a common fenforium ; by the medium of which their mufcles are excited into aCtion. Laftly, in many flowers the anthers, when mature, approach the ftigma ; in others the female or- gan approaches to the male. In a plant of collinfonia, a branch of which is now before me, the two yellow ftamens are about three eighths of an inch high, and diverge from each other, at an angle of about fifteen degrees ; the purple ftyle is half an inch high, and in fome flowers is now applied to tire ftamen on the right hand, and in others to that of the left ; and will, I fuppofe, change place to-morrow in thofe where the an- thers have not yet effufed their power. I afk, by what means are the anthers in many flow r ers, and ftigmas in other flowers, directed to find their paramours ? How" do either of them know that the other exifts in their vi- cinity ? Is this curious kind of florge produced by mechanic attraction, or by the fenfation of love? The latter opinion is fupportedby the ftrongeft analogy, becaufe a re-produ£tion of the fpecies is the confequence ; and then another organ of fenfe muft be wanted to direCt thefe vegetable amourettes to find each other, one probably analogous to our fenfe of fmell, which in the animal world direCts the new-born infant to its fource of nourifhment, and they may thus poffefs a faculty of perceivirtg as well as of producing odours. M Thus 7'6 PRODUCTION. OF IDEAS. Sect. XIV. i. Thus, befides a kind of tafte at the extremities of their roots, iknilar to that of the extremities of our ladteal veffels, for the purpofe of felecting their proper food; and befides different kinds of irritability reliding in the various glands, which feparate honey, wax, refin, and other juices from their blood ; vegetable life feems to poffcfs an organ of fenfe to dif- tinguifh the variations of heat, another to diftinguifh the va- rying degrees of moifture, another of light, another of touch, and probably another analogous to our fenfe of fmell. To thefe muft be added the indubitable evidence of their paffion of love ; and I think we may truly conclude, that they are furniih- ed with a common fenforium belonging to each bud, and that they mull; occafionally repeat thofe perceptions either in their dreams or waking hours, and confequently poffefs ideas of fo many of the properties of the external world, and of their own exiftence. SECT. XIV. OF THE PRODUCTION OF IDEAS. I. Of material and immaterial beings. Doftrinc of St. Paul. II. I. Of the fenfe of touch. Of fclidity. 1 . Of figure, Motion. Time. Place. Space. Number. 3- Of the penetrability of matter. 4. Spirit of ani- mation pofifeffes folidity, figure, vifibility, (sic. Of fipi- rits and angels. 5. The exiftence of external things. III. Of vijion. IV; Of hearing. V. Of fmell and tafle. VI. Of the organ of fenfe by which we perceive heat and cold, not by the fenfe of touch. VII. Of the fenfe of extenfion-, the whole of the locomotive mu files . may be confidercd as one organ of fenfe. VIII. Of the fciifies of hunger , thirfi , want of frcjh air, fuckling chil- dren, and lufi. IX. Of many other organs of fenfe be- longing to the glands. Of painful fenfaticns from the excefs of light , preffure , heat , itching , cauflics, and electricity. I. PHILOSOPHERS have been much perplexed to under- hand, in what manner we become acquainted with the exter- nal world; infomuch that Dr. Berkly even doubted its exig- ence, from having obferved, (as he thought) that none of our ideas refemble their correfpondent objects. Mr. Hume afferts, that our belief depends on the greater diftindlnefs or energy qf our ideas from perception ; and Mr- Reid has lately contended. Sect. XIV. 2. PRODUCTION OF IDEAS. 7,7 that our belief of external objeds is an innate principle, necef- farjly joined with our perceptions. So true is the obfervation of the famous Malbranch, “ that our fenfes are not given us to difcover the eifences of things, but to acquaint us with the means of preferving our exiftence,” (L. I. ch. v.) a melancholy reflection to philofophers ! Some philofophers have divided all created beings into ma- terial and immaterial: the former including all that part of be- ing, which obeys the mechanic laws of adion and re-adion, but which can begin no motion of itfelf; the other is the caufe of all motion, and is either termed the power of gravity, or of fpecific attraction, or the fpirit of animation. This immate- rial agent is fuppofed to exift in or with matter, but to ne quite diftind from it, and to be equally capable of exiftence, after the matter, which now poffeffes it, is decompofed. Nor is this theory ill fupported by analogy, fince heat, ■eleCtricity, and magnetifm can be given to or taken from a ■piece of iron; and muft therefore exift, whether feparated from the metal, or combined with it. From a parity of rea- foning, the fpirit of animation would appear to be capable of exifting as well feparately from the body as with it. I beg to be underftood, that I do not with to difpute about words, and am ready to allow, that the powers of gravity, fpecific attraction, eledricity, .magnetifm, and even the fpirit of animation, may confift of matter of a finer kind ; and to believe, with St. Paul and Malbranch, that the ultimate caufe only of all motion is immaterial, that is, God. St. Paul fays, “ in him we live, and move, and have our being;” and, in the 15th chapter of the Corinthians, diftinguifhes between the pfyche or living fpirit, and the pneuma ©r reviving fpirit. By the words fpirit of animation or fenforial power, I mean «niy that animal life which mankind poflefTes in common with brutes, and in fome degree even with vegetables, and leave the confideration of the immortal part of us, which is the objeCl of religion, to dnofe who treat of revelation. II. J. Of the Senfe of Touch. The firft ideas we become acquainted with, are thofe of the fenfe of touch ; for the foetus muft experience fome varieties of agitation, and exert fome mufcular adion, in the womb; and may, with great probability, be fuppofed thus to gain fome ideas ■of its own figure, of that of the uterus, and of the tenacity of the fluid that lurrounds it, (as appears from the fads mention- ed in the fucceeding Sedion upon Inftind.) Many of the organs of fenfe are confined to a final! part of the PRODUCTION OF IDEAS. Sect. XIV. 2 . The body, as the noflrils, ear or eye, whilfl the fenfe of touch is difFufed over the whole fkin, but exifts, with a more exqui- fite degree of delicacy, at the extremities of the fingers and thumbs; and in the lips. The fenfe of touch is thus very com- modioufly difpofed, for the purpofe of encompafling fmaller bo- dies, and for adapting itfelf to the inequalities of larger ones. The figure of finall bodies feems to be learnt by children by their lips as much as by their fingers ; on which account they put every new objedb to their mouths, when they are fatiated with food, as well as when they are hungry. And puppies feetn to learn their ideas of figure principally by the lips in their mode of play. We acquire our tangible ideas of objects either by the fim- ple preffure of this organ of touch againft a folid body, or by moving our organ of touch along the furface of it: in the for- mer cafe, we learn the length and bieadth of the objcdf by the quantity of our organ of touch that is impreffed by it : in the latter cafe, we learn the length and breadth of objedts by the continuance of their preffure on our moving organ of touch. It is hence that we are very flow in acquiring our tangible ideas, and very flow in recolledfing them ; for it I now think of the tangible idea of a cube, that is, if I think of its figure, I rnuft conceive myfelf as pafling my fingers over it, and feem in fome meafure to feel die idea, as I formerly did the impref- fion at the ends of them, and am thus very flow in diftindfly recolledfing it. When a body compreffes any part of our fenfe of touch, what happens ? Firfl, this part of our fenforium undergoes a mechanical compreflion, which is termed a ftimulus ; fecond- ly, an idea, or contradbion of a part of die organ of fenfe, is excited; thirdly, a motion of the central parts, or of the whole fenforium, which is termed fenfarion, is produced ; and thefe three conftitute the perception of folidity. 2. Figure , Motion , Time , Place, Space , Number. No one will deny, that the medulla of the brain and nerves lias a certain figure ; which, as it is difFufed through nearly the whole of die body, mud have nearly the figure of that body. Now it follows, that the fpirit of animation, or living principle, as it occupies this medulla, and no other part, (which is evinced by a great variety of cruel experiments on living animals) it follows, that dais fpirit of animation has alfo the fame figure as the medulla above delcribed. I appeal to common fenfe ! the fpirit of animation adds ; where does it adt ? It adds wherever there is the medulla above mentioned ; and 79 Sect. XIV. 2 . PRODUCTION OF IDEAS. and that whether the limb is yet joined to a living animal, or whether it be recently detached from it ; as the heart of a viper or frog will renew its contra&ions, when pricked with a pin, for many minutes of time after its exfedtion from the body.— Does it a6t any where elfe ? No ; then it certainly exifts in this part of fpace, and no where elfe ; that is, it hath figure ; name- ly, the figure of the nervous fyftem, which is nearly the figure of the body. When the idea of foliditv is excited, as above explained, a part of theextenfive organ of touch is comprefled by fome external body; and this part of the fenforium fo com- preffed, exactly refembles in figure , the figure of the body that comprefled it. Hence, when we acquire the idea of foiidity, we acquire, at the fame, the idea of figure ; and this idea of figure, or motion of a part of the organ of touch, exactly re- fembles, in its figure , the figure of the body that occafions it , and thus exadfly acquaints us with this property of the exter- nal world. Now, as the whole univerfe, with all its parts, pofiefles a certain form or figure, if any part of it moves, that form or figure of the whole is varied: hence, as motion is no other than a perpetual variation of figure, our idea of motion is alfo a real refemblance of the motion that produced it. It may be faid, in objedlion to this definition of motion, that an ivory globe may revolve on its axis, and that here will be a motion without change of figure. But the figure of the parti- cle x on one fide of this globe, is not the fiame figure as the figure of y on the other fide, any more than the particles them- felves are the fame, though they are fimilar figures ; and hence they cannot change place with each other, without difturbing or changing the figure of the whole. Our idea of time is from the fame fource, but is. more ab- ftradfed, as it includes only the comparative velocities of thefe variations of figure hence, if it be afked, how long was this book in printing ? it may be anfwered, whilft the fun was paf- fing through Aries. Our idea of place includes only the figure of a group of bodies, not the figure of the bodies themfelves. If it be slic- ed, where is No'ttinghamfhire ? the anfwer is, it is furrounded by Derbyfhire, Lincolnfliire, and Leicefterfhire : hence place is our idea of the figure of one body furrounded by the figures of other bodies. ' - The idea of space is a more abftracffed idea of place ex- cluding the group of bodies. The idea of number includes only the particular arrange- ments, or diftributions of * group of bodies, and is therefore ; " 1 . only So PRODUCTION OF IDEAS. Sect. XIV. 2. only a more abftracted idea of the parts of tire figure of the group of bodies : thus, when I fay England is divided into forty counties, I only fpeak of certain divifions of its figure. Hence arifes the certainty of the mathematical fciences, as they explain thefe properties of bodies, which are exactly re- fembled by our ideas of them, whilft we are obliged to col- led! almoft all our other knowledge from experiment ; that is, by obferving the effects exerted by one body upon anodier. 3. Of the Penetrability cf Matter. The impoffibilily of two bodies .exifting together, in the fame fpace, cannot be deduced from our idea of folidity, or of figure. As foon as we perceive the motions of objects that furround us, and learn that we .poflefs a power to move our own bodies, we experience, that thofe -objects, which excite in us the idea of folidity and of figure, oppofe this voluntary movement of our own organs; as whilft I endeavour to oomprefs between my hands an ivory ball into a fpheroid. And we are hence taught by experience, tixat our own body, and thofe which we touch, cannot exift in the fame part of fpace. But this by no means demonftrates, that no two bodies can exift together in the fame part cf fpace. Galiiaeo, in the pre- face to his works, feems to' be of opinion, that matter is nor impenetrable. Mr. .Michel, and Mr. Bofcowich, in his Theo- ria. Philof. Natur. have efpoufed this hypothefis : which has been lately published bv Dr. Prieftley, to whom the world is much indebted for fo many important difeoveries in fcience. (Hift. of Light and Colours, p. 391.) The uninterrupted puflage of light through tranfparent bodies, of the eledtric jether through metallic and aqueous bodies, and of the magnetic effluvia through all bodies, would feem to give fome probabi- lity to this opinion. Hence it appears, that beings may exift without pofleffing the property of folidity, as well as they can exift without polleffing the properties which excite our fmell or tafte, and can thence occupy fpace without detruding other bodies from it; but we cannot become acquainted with fuch beings by our fenfe of touch, any more than we can with odours or flavours without our fenfes of fmell and tafte. But that any being can exift without exifting in fpace, is to mv ideas utterly incomprehenfible. My appeal is to common fenfe. To be implies a when and a where ; the one is com- paring it with the motions of other beings, and the other with their fituations. If there was but one objedl, as the whole creation may be confide red Sect. XIV. 2. PRODUCTION OF IDEAS. Si eonfidered as one object, then I cannot afk where it exifts ? for there are no other objects to compare its htuation with. Hence, if any one denies that a being exifts in fpace, he de- nies that there are any other beings but that one ; for to an- fwer the queflion, “ Where does it exifti” is only to men- tion the lituation of the objects that lurround it. In the fame manner, if it be afked, “ When does a being exift;?” the anfvver only jpecihes the fucceffive motions ei- ther of itfelf, or of other bodies : hence, to fay a body exifts not in time, is to fay, that there is, or was, no motion in the world. 4. Of the Spirit of Animation. But though there may exift beings in the univerfe, that have not the property of folidity ; that is, which can poffefs any part of fpace, at the fame time that it is occupied by other bo- dies ; yet there may be other beings diat can aftume this pro- perty of folidity, or difrobe themielves-of it occaftonally, as we are taught of lpirits, and of angels ; and it would leem, that the spirit of animation muft be endued with this property, otherwife how could it occaiionally give motion to the limbs of animals ? — or be itfelf ftimulated into motion by the obtruftons of furrounding bodies, as of light, or odour ? If the fpirit of animation was always neceffarily penetrable, it could not influence or be influenced by the folidity of mat- ter ; they would exift together, but could not detrude each other , from the part of fpace where they exift ; that is, they could not communicate motion to each other. No two things can influ- ence or affeft each other, which have not feme property com- mon to both of them-, for, to influence or affedl another body, is to give or communicate fome property to it, that it had not before; but how can one body give that to another which it does not poffefs itfelf? — The words imply, that they muft agree in having the power or faculty of pofleffing fome com- mon property. Thus, if one body removes another from the part of fpace that it poffeffes, it muft have the power of occu- pying that fpace itfelf: and if one body communicates heat or motion to another, it follows, that they have alike the property of pofleffing heat or motion. Hence, the fpirit of animation, at the time it communicates or receives motion from folid bodies, muft itfelf poflefs fome pro- perty of folidity. And in confequence, at the time it receives other kinds of motion from light, it muft poffefs that property which light poffeffes, to communicate that kind of motion ; and for which no language has a name, unlefs itmav be termed Vif'I- bilitv. 82 PRODUCTION OF IDEAS. Sect. XIV. 2. bility. And, at the time it is ftimulated into other kinds of ani- mal motion, by the particles of fapid and odorous bodies affect- ing the fenles of tafte and fmell, it mu ft refemble thefe particles of flavour, and of odour, in poffeding fome fimilar or corref- pondent property ; and for which language has no name, un- lefs we may ufe the words Saporofity and Odorofity for thofe common properties which are poffefTed by our organs of taft£ and fmell, and by the particles of fapid and odorous bodies ; as the words Tangibility and Audibility may poffefs die common property poffefTed by our organs of touch, and of hearing, and by the lolid bodies, or their vibrations, which affedt thofe organs. 5. Finally, though the figures of bodies are in truth refem- bled by the figure of the part of the organ ot touch, which is ftimulated into motion ; and that organ relembles the folid bo- dy which ftimulates it, in its property of folidity ; and though the fenfe of hearing refembles the vibrations of external bo- dies, in its capability of being ftimulated into motion by thole vibrations ; and though our other organs of fenfe refemble the bodies that ftimulate them, in their capability of being ftimu- lated by them ; and we hence become acquainted with thefe properties of the external world; yet, as we can repeat all thefe motions of our organs of fenfe by the efforts of volition, or in confequence of the fenfation of pieafure or pain, or by their affociation with other fibrous motions, as happens in our reve- ries or in fleep, there would ftill appear to be fome difficulty in demonftrating the exiftence of any thing external to us. In our dreams we cannot determine this circumftance, bc- caufe our power of volition is iufpended, and the ltimuli ot external objedts are excluded ; but in our waking hours we can compare our ideas belonging to one fenfe, with thofe be- longing to another, and can thus diftinguiih the ideas occa- fioned by irritation, from thofe excited by fenlation, volition, or afTociation. Thus, if the idea of the fweetnefs of iugar ftrould be excited in our dreams, the whitenefs and hardnels of it occur at the fame time by affociation ; and we believe a material lump of fugar prelent before us. But if, in our waking hours, the idea of the fweetnels ot fugar occurs to us, the ftimuli of furrounding objedts, as the edge of the table on which we prefs, or green colour ot the grafs on which we tread, prevent the other ideas of the hardnels and white - nefs of the fugar from being exerted by affociation. Or it they fhould occur, we voluntarily compare them with the ir- ritative ideas of the table or grafs above mentioned, and detect their fallacy. We can thus diftinguiih the ideas caufed by. Sect. XIV. 3. PRODUCTION OF IDEAS. 83 the ftimuli of external objcdls, from thofe which are introduc- ed by affociation, fenfation, or volition ; and during our wak- ing hours, can thus acquire a knowledge of the external world. Which, neverthelefs, we cannot do in our dreams, becaufe we have neither perceptions of external bodies, nor the power of volition, to enable us to compare them with the ideas of imagination. III. OfVifion . Our eyes obferve a difference of colour, or of fhade, in the prominences and depreffion of objedls, and that thofe fhades uniformly vary, when the fenfe of touch obferves any varia- tion. Hence, when the retina becomes ftimulated by colours or fhades of light in a certain form, as in a circular fpot, we know by experience, that this is a fign, that a tangible body is before us ; and that its figure is refembled by the miniature fi- gure of the part of the organ of vition that is thus ftimulated. Here, whilft the ftimulated part of the retina relembles ex- actly the viftble figure of the whole in miniature, the various kinds of ftimuli form different colours, mark the viftble figures of the minuter parts ; and, by habit, we inftantly recall the tan* gible figures. Thus, when a tree is the objedt of fight, a part of the reti- na, refembling a flat branching figure, is ftimulated by vari- ous fhades of colours ; but it is by fuggeftion, that the gibbo- ftty of the tree, and the mofs that fringes its trunk, appear be- fore us. Thefe are ideas of fuggeftion, which we feel or at- tend to, affociated with the motions of the retina, or irritative ideas, which we do not attend to. So that, though our viftble ideas refemble in miniature the outline of the figure of coloured bodies, in other refpedfs they ferve only as a language, which, by acquired affociations, in- troduce the tangible ideas of bodies. Hence it is, that this fenfe is fo readily deceived by the art of the painter, to our amufement and inftrudlion. The reader will find much very curious knowledge on this fubjedl, in Bifhop Berkley’s Effay on Vifion, a work of great ingenuity. The immediate objedt, however, of the fenfe of vificn, is light ; this fluid, though its velocity is fo great, appears to have no preceptible mechanical impulfe, as was mentioned in the third Sedtion, but feems to ftimulate the retina into animal motion by its tranfmiflion through this part of the fenforium: for though the eyes of cats or other animals appear luminous in obfcure places, yet it is probable, that none of the light, which falls on the retina, is refledted from it, but adheres to or enters into combination with the choroide coat behind it. N The 84 PRODUCTION OF IDEAS. Sect. XIV. 4. The combination of die particles of light with opake bo- dies, and therefore with the choroide coat of the eve, is evinc- ed from the heat, which is given out, as in other chemical combinations. For the fun beams communicate no heat in their paflfage through tranfparent bodies, with which they do not combine, as the air continues cool even in the focus of the largeft burning -glaffes, which in a moment vitrifies a par- ticle of opaque matter. IV. Of the Organ of Hearing. It is generally believed, that the tympanum of the ear vi- brates mechanically, when expofed to audible founds, like the firings of one mulical inflrument, when the fame notes arc flruck upon another. Nor is this opinion improbable, as the rnufcles and carrileges of the lyranx are emploved in produc- ing variety of tones by mechanical vibration : fo the rnufcles and bones of the ear feem adapted to increafe or diminifh the tendon of the tympanum, for the purpofes of fimilar mecha- nical vibrations. But it appears from diflfecfion, that tire tympanum is not the immediate organ of hearing, but that, like the humours and cornea of the eye, it is only of ufe to prepare the objedf for tire immediate organ. For the portio mollis of the auditory nerve is not fpread upon the tympanum, but upon the viflibu- lum, and cochlea, and femicircular canal of the ear ; while, between the tympanum and the expaniion of the auditory nerve, the cavity is laid, by Dr. Cotunnus and Dr. Meckel, to be filled with water ; as they had frequently obferved by freezing the heads of dead animals before they di fleeted them; and wa- ter being a more denfe fluid than air, is much better adapted to the propagation of vibrations. We may add, that even the external opening of the ear is not abfolutely neceflary for the perception of found : for fome people who, from thefe defeats, would have been completely deaf, have diftinguiflied acute or grave founds bv the tremours of a flick held between their teeth, propagated along the bones of the head. (Haller. Phyf. T.V. p.295.) Hence it appears, that the immediate organ ot hearing is not affedted by the particles of the air themfelves, but is ftimuiated into animal motion by the vibrations of them. And it is pro- bable, from the loofe bones which are found in the heads of fome fifties, that the vibrations of water are fenfibie to the in- habiants of that element by a fimilar organ. The motions of the atmofphere, which we become acquaint- ed with by the fenfe of touch, are combined with its folidity, weight, Sect. XIV. 5. PRODUCTION OF IDEAS. 8,5 weight, or vis inertias; whereas thofe that are perceived by this organ depend alone on its elafticity. But though the vi- brati jn of the air is the immediate objedt of the fenfe of hear- ing, yet the ideas we receive by this fenfe, like thole received from light, are only as a language, which, by acquired aiToci- ations, acquaints us with thofe motions of tangible bodies which depend on their elafticity, and which we had before {earned by our fenfe of touch. V, Of Smell and of Tafe. The objedfs of fmell are diiTolved in the fluid atmofphere, and thofe of tafte in the faliva, or other aqueous fluid, for the better defuflng them on their refpedtive organs, which feem to be ftimulated into animal motion, perhaps by the chemical af- finities of thefe particles, which conftitute the fapidity and odorofiiy of bodies with the nerves of fenfe, which perceive them. Mr. Volta has lately obferved a curious circumftance rela- tive to our fenfe of tafte. If a bit of clean lead and a bit of clean lilver be feparately applied to the tongue and palate, no tafte is perceived ; but by applying them in contadf, in refpedt to the parts out of the mouth, and nearly fo in refpedt to the parts which are immediately applied to the tongue and palate, a faline or acidulous tafte is perceived, as of a fluid like a itream of eledtricity palling from one of them to the other. This new application of the fenfe of tafte deferves further inveftiga- tion, as it may acquaint us with new properties of matter. From the experiments above mentioned of Galvani, Volta, Fowler, and others, it appears, that a plate of zinc and a plate of lilver have a greater eftedt than lead and lilver. If one edge of a plate of lilver, about the lize of half a crown piece, be placed upon the tongue, and one edge of a plate of zinc, about the fame lize, beneath the tongue, and if their oppofite edges are then brought into contadf before the point of the tongue, a tafte is perceived at the moment of their coming into contadf : fecondly, if one of the above plates be put between the upper lip and the gum of the fore-teeth, and the other be placed under the tongue, and their exterior edges be then brought into con- tadf in a darkifh room, a flalh of light is perceived in the eyes. Thefe etfedfs, I imagine, only Ihew the fenfibility of our nerves of fenfe, to very fmall quantities of the eledfric fluid, as it pafles through them ; for I fuppofe thele fenfations are oc- cafioned by flight eledfric Ihocks, produced in the following manner. By the experiments publiflied by Mr. Benner, with his ingenious doubler of eledtricity, which is the greatelf dif- covery 86 PRODUCTION OF IDEAS. Sect. XIV 6. coverv made in that fcience fmce the coated jar, and the educ- tion of lightning from the (kies, it appears that zinc was always found minus, and filver was always found plus, when both of them were in their feparate ftate. Hence, when they are placed in the manner above defcribed, as foon as their exterior edges come nearly into contact, fo near as to have an extreme- ly thin plate of air between them, that plate of air becomes charged in the fame manner as a plate of coated glafs; and is, at the fame inftant, difcharged through the nerves of tafte or of fight, and gives the fenfations, as above defcribed, of light or of faporocity ; and only Ihews the great fenfibility of thefe organs of fenfe to the ftimulus of the eiecftric fluid in fuddenly palling through them. VI. Of the Safe of Heat. There are many experiments in chemical writers, that evince the exiftence of heat as a fluid element, which covers and per- vades all bodies, and is attracted by the folutions of fome of them, and is detruded from the combination of others. Thus, from the combinations of metals with acids, and from thefe combinations of animal fluids, which are termed fecretions, this fluid matter of heat is given out amongft the neighbour- ing bodies ; and in the folutions of falts in water, or of water in air, it is abforbed by the bodies that furround them; whilft, in its facility in paffing through metallic bodies, and its difficulty in pervading refins and glals, it refembles .the properties of the define aura ; and is like that excited by friction, and feems like that to gravitate amongft other bodies in its uncombined ftate, and to find its equilibrium. There is no circumftance of more confcquence in the ani- mal economy, than a due proportion of this fluid of heat; for the digeftion of our nutriment in the ftomach and bowels, and the proper qualities of all our fecreted fluids, as they are pro- duced or prepared, partly by animal, and partly by chemical proceffes, depend much on the quantity of. heat, the excels of which, or its deficiency, alike gives us pain, and induces r^-to avoid the circumftances that occalion them. And in this the perception of heat effentially differs from the perceptions of tire fenfe of touch, as we receive pain from too great preffure of folid bodies, but none from the abfence of it. It is hence pro- bable, that nature has provided us with a let of nerves ror the perception of this fluid, which anatomilts have not yet attend- ed to. There may be fome difficulty in the proof of this aflertion : if we look at a hot lire-, we experience no pain of the optic - 7- nerve, Sect. XIV. 7- PRODUCTION OF IDEAS. 87 nerve, though the heat along with the light muff be concen- trated upon it. Nor does warm water or warm oil poured into the ear give pain to the organ of hearing ; and hence, as thefe organs of fenfe do not perceive fmall exceffes or deficien- cies of heat, and as heat has no greater analogy to the folidity or to the figures of bodies, than it has tp their colours or vi- brations, there feems no fufficient reafon for our afcribing the perception of heat and cold to the fenfe of touch, to which it has been generally attributed, either becaufe its is diffufed be- neath the whole lkiii like the fenfe of touch, or owing to the inaccuaracy of our obfervations, or the defecSi of our lan- guages. There is another circumftance which would induce us to believe that the perceptions of heat and cold do not belong to the organ of touch ; fince the teeth, which are the lead adapted For the perceptions of folidity or figure, are the molt fenfible to heat or cold ; whence we are forewarned from fwallowing thofe materials, whofe degree of coldnefs or of heat would in- jure our ftomachs. The following is an extract from a letter of Dr. R. W. Darwin, of Shrewfbury, when he was a ftudent at Edinburgh. “ I made an experiment yefterday in ourhofpital, which much •favours your opinion, that the fenfation of heat and of touch depend on different fets of nerves. A man who had lately re- covered from a fever, and was Hill weak, was ieized with vi- olent cramps in his legs and feet, which were removed by opi- ates, except that one of his feet remained infehfibie. Mr. Ew- art pricked him with a pin in five or fix places, and the pa- tient declared he did not feel it in the leaft, nor was he fenfi- ble of a very (mart pinch. I then held a red hot poker at lome diftance, and brought it gradually nearer, till it came within three inches, when he afferted that he felt it quite dif- tindlly. I fuppofe fome violent irritation on the nerves of touch had earned the cramps, and had left them paralytic ; while die nerves of heat, having fuffered no increafe of fti- rnuius, retained their irritability.” VII. Of the Senfe of Extenfion. The organ of touch is properly the fenfe of preffure, but the mufcular "fibres themfelves conftitute the organ of fenfe, ihat feels extenfion. The fenfe of preffure is always attend- ed with, tire ideas of the figure and folidity of the objedf, nei- ther of which accompany cur perception of extenfion. The whole fet of muicles, whether they are hollow ones, as the heart, arteries, and inteftines,' or longitudinal ones attached to bones, 83 PRODUCTION OF IDEAS. Sect. XIV. 7. bones, contract themfelves, ' whenever they are flimulatedby forcible elongation ; and it is ohfervable, that the white muf- cles, which conftitute the arterial fyftem, feem to be excited into contradlion from no other kinds of ftimulus, according to the experiments of Haller. And hence the violent pain in fome inflammations, as in the paronychia, obtains immediate relief by cutting the membrane, that was ftretched by the tu- mour of the fubjacent parts. Hence the whole rnufcular fyftem maybe confidered as one organ of fenfe, and the various attitudes of the body, as ideas belonging to this organ ; of many of which we are hourly con- scious, while many r others, like the irritative ideas of the other fenfes, are performed without our attention. When the mufcles of the heart ceafe to adl, the refluent blood again diftends or elongates them; and thus irritated, they contract as before. The fame happens to the arterial fyftem, and I fuppofe to the capillaries, inteftines, and yarious glands of the body. When the quantity of urine, or of excrement, diftends the bladder, or redtum, thofe parts contract, and exclude their contents, and many other mufcles, by aflbeiation, adt along with them ; but if thefe evacuations are not loon complied with, pain is produced by a little further extenfion of the mufcular fibres: a fimilar pain is caufed in the mufcles, when a limb is much extended for the redudtion of diflocated bones ; and in the punifhment of the rack, and in the painful cramps of the calf of the leg, or of other mufcles ; for a greater degree of con- tradtion of a mufcle, than the movement of the two bones to which its ends are afExed will admit of, muft give fimilar pain to that which is produced bv extending it beyond its due length. And the pain from pundtures or inciiions arifes from the dif- tention of the fibres, as the knife pafles through them ; for it nearly ceafes as foon as the divifion is completed. All thefe motions of the mufcles, that are thus naturally ex- cited by the ftimulus of diftending bodies, are alfo liable to be called into ftrong adtion, by their catenation with the irrita- tions or fenfations produced by the momentum of the progref- live particles of blood in the arteries, as in inflammatory' fe- vers ; or by acrid fubftances on other fenfiblc organs, as in the ftrangury, or tenefmus, or cholera. We fliall conclude this account of the fenfe of extenfion by obferving, that the want of its objedt is attended with a difa- greeable ienfation, as well as the excels of it. In thofe hollow mufcles which have been accuftomed to it, this difagreeable fenfation is called faintnefs, emptinefs, and finking ; and, when Sect. XIV. 8. PRODUCTION OF IDEAS. 89 itarifes to a certain degree, is attended with fyncope, or a total quiefcence of all motions but the internal irritative ones, as happens from fudden lofs of blood, or in the operation of tap- ping in the dropfy. VIII. Of the Appetites of Hunger, Thirji, Heat, Extenfon, the \vant of frejh Air, animal Love , and the fuck ling of Children. , Hunger is mod probably perceived by thofe numerous rami- fications of nerves that are feen about the upper opening of the ftomach ; and thirft, by the nerves about the fauces, and the top of the gula. The ideas of thefe fenles are few in the generality of mankind, but are more numerous in thofe who, by difeafe or indulgence, defire particular kinds of foods or liquids. A fenfe of heat has already been fpoken of, which may with propriety be called an appetite, as we painfully defire it, when it is deficient in quantity. A fenfe of extenfion may be ranked amongft thefe appetites, fince the deficiency of its object gives difagreeable fenfation : when this happens in the arterial fyfiem, it is called faintnefs, and feems to bear fome analogy to hunger and to cold ; which, like it, are attended with emptinefs of a part of the vafcular fyfiem. The fenfe of want of frefli air has not been attended to, but is as diftindt as the others, and thefirft perhaps that we ex- perience after our nativity : from the want of the objedt of this fenfe many difeafes are produced, as the jail-fever, plague, and other epidemic maladies. Animal love is another appe- tite, which occurs later in life ; and the females of ladtiferous animals have another natural inlet of pleafure or pain from the fuckling their offspring. The want of which, either owing to the death of their progeny, or to the fafhion of their country, has been fatal to many of the fex. The males have alfo pec - toral glands, which are frequently turgid with a thin milk at their nativity, and are furnifhed with nipples, which eredt on titillation like thofe of the female ; but which feem now to be of no further ufe, owing perhaps to fome change which thefe ani- mals have undergone in the gradual progreffion of the forma- tion of the earth, and of all that it inhabit. Thefe feven laft mentioned fenfes may properly be termed appetites, as they differ from thofe of touch, fight, hearing, tafte, and fmell, in this refpedt ; that they are affected with pain, as well by the defect of their objects, as by the excefs of them, which is not fo in the latter. Thus cold and hunger give us pain, as well as an excefs of heat or fatiety : but it is not fo with darknefs and filence. IX, Before we conclude this Section on the organs of fenfe, we 9 ® CLASSES OF IDEAS. Sect. XV. i. we mu ft obferve, that, as far as we know, there are many more fenfes than have been here mentioned, as every gland feems to be influenced to feparate from the biood, or to abforb from the cavities of the body, or from the atmofphere, its appropriated Laid, by the ftimulus of that fluid on the living gland; and not by mechanical capillary abforption, nor by chemical affinity. H ence it appears, that each of thefe glands mufthave a pecu- liar organ to perceive thefe irritations ; but, as thefe irritations are not lucceeded by fenfation, they have not acquired the names of fenfes. However, when thefe glands arc excited into motions ftrong- c-r than ufual, either by the acrimony of their fluids, or by their own irritability being much increafed, then the fenfation of pain is produced in them as in all the other fenfes of the bodv ; mid thefe pains are all of different kinds ; and hence the glands at this time really become each a different organ of fenfe, though thefe different kinds of pain have received no names. Thus, a great excefs of light does not give die idea of light, but of pain ; as in forcibly opening the eye when it is much inflamed. The great excefs of'preiTure or diftention, as w hen the point of a pin is preffed upon our fkin. produces pain, (and when this pain of the fenfe of touch is {lighter, it is term- , cd itching or tickling) without any idea of fchdity or of figure : an excels of heat produces fmarting, of cold another kind of pain: it is probable by this fenfe of heat the pain produced by cauftic bodies is perceived, and of electricity, as all theie are flu- ids, that permeate, diftend, or decompofe the parts that feel them. SECT. XV. OF THE CLASSES OF IDEAS. I. I. Ideas received hi tribes. 2. IVe combine them fur- ther, cr abflrad from theje tribes. 3. Complex ideas. 4. Compounded ideas. 5. Simple ideas, modes, JubJien- ccs , relations ; general ideas. 6. Ideas oj reflexion. J. Aleatory and imagination imp cr fell ly dejined. 1 acal pre- fence. Alemorandum-mngs. II. I. Irritative ideas; perception. 2. Senfitive ideas ; imagination. 3. F dun- tar v ideas ; recollect ion. 4. Affoctuted ideas ; figgejiion. III. 1. Definitions of perception; memory. 2 . Reef oil- ing, judgment, doubting, dfiingm fling, comparing. 3. Invention. 4 - Confcioufncfs. 5 - Identity. 6. L.apje of time. 7. I rse-vdil. I. AS the conftituen? elements of the material world are Oii'v perceptible to our organs of fenie in a ftate of combine- Sect. XV. i. CLASSES OF IDEAS, 9 1 rion ; it follows, that the ideas or fenfual motions excited by them, are never received fingly, but ever with a greater or lefs degree of combination. So the colours of bodies, or their hard- neffies, occur with their fingers : every fmeli and tafte has its degree of pungency, as well as its peculiar flavour : and each note in mulic is combined with the tone of fome inftrument. It appears from hence, that we can be fenftble of a number of ideas at the fame time, fuch as the whitenefs, hardnefs, and coldnefs of a fnow-ball, and can experience, at the fame time, many irritative ideas of furrounding bodies, which we do not attend to, as mentioned in Sedf. VII. 3. 2. But thofe ideas which belong to the fame fenfe, feem to be more eafily com- bined into fynchronous tribes, than thofe which were not re- ceived by the fame fenfe, as we can more eafily think of the whitenefs and figure of a lump of fugar at the fame time, than the whitenefs and fweetnefs of it. 2. As thefe ideas, or fenfual motions, are thus excited with greater or lefs degrees of combination, fo we have a power, when we repeat them either by our volition orfenfation, to in- creafe or diminifh this degree of combination ; that is, to form compounded ideas from thofe which were more Ample, and abftrad! ones from thofe which were more complex, when they were firft excited; that is, we can repeat a part, or the whole of thofe fenfual motions which did conftitute our ideas of perception ; and the repetition of which now conftitutes our ideas of recolledfion, or of imagination. 3. Thofe ideas which we repeat without change of the quantity of that combination, with which w 7 e firft received them, are called complex ideas, as when you recoiled! Weft- minfter Abbey, or the planet Saturn ; but it muft be obferved, that thefe complex ideas, thus re-excited by volition, fenfation, or afTociation, are feldom perfed! copies of their correfpond- ent perceptions, except in our dreams, where other external ob- jedls do not detradl our attention. 4. Thofe ideas which are more complex than the natural objects that firft excited them, have been called compounded ideas, as when we think of a fphinx or griffin. 5. And thofe that are lefs complex than the correfpondent natural objedts, have been tenned abftradted ideas : thus fweet- nefs, and whitenefs, and folidity, are received at the fame time from a lump of fugar ; yet I can recoiled! any of thefe qualities without thinking of the others, that were excited along with them. When ideas are fo far abftradled as in the above example, they have been termed fimple by the writers of metaphylics, O and Classes of ideas. Sect. XV, u 9 * and feetn indeed to be more complete repetitions of the ideas or fenfual motions, originally excited by external objedts. Other claffes of thefe ideas, where the abftraction has not been fo great, have been termed, by Mr. Locke, modes, fub- ftances, and relations ; but they feem only to differ in their de- gree of abftraction from the complex ideas that were at firft excited ; for as theie complex or natural ideas are themfelves im- perfedt copies of their correfponaent perceptions ; fo thefe ab- ftradt or general ideas are only (till more imperfedt copies of the fame perceptions. Thus, when I have feen an object but once, as a rhinoceros, my abflradt idea of this animal- is the fame as my complex one. I may think more or lefs diftinctlv of a rhinoceros, but it is the very rhinoceros that I faw, or fome part or property of him which recurs to my mind. But when any clafs of complex objedts becomes the fubjedt of converfation, of which I have feen many individuals, as a caftle or an army, fome property or circumftance belonging to it is peculiarly alluded to ; and then I feel in my own mind that my abftradc idea of this complex objedt is only an idea of that part, property, or attitude of it, that employs the prefent converfation, and varies with every fentence that is fpoken con- cerning it. So, if any one fhouid fay, “ one may lit upon a horfeiafer than on a camel,” my abflradt idea of the two ani- mals includes only an outline of the level back of the one, and the gibbolity on the back of the other. What noife is that in the ftreet ? Some horfes trotting over the pavement. Here my idea of the horfes includes principally the fhape and mo- tion of their legs. So alfo the abflradt ideas of goodnefs and courage are ftill more imperfedt reprefentations of the objedts they were received from ; for here we abflradt the material parts, and recolledt only the qualities. Thus, w'e abflradt fo much from fome of our complex ideas, that at length it becomes difficult to determine of what percep- tion they partake ; and in many inflances our idea feems to be no other than of the found or letters of the word, that Hands for the colledtive tribe, of which we are faid to have an ab- flradted idea, as noun, verb, chimera, apparition. 6. Ideas have been divided into thofe of perception, and thofe of refiedtion ; but as whatever is perceived mull be external to the organ that perceives it, all our ideas mull originally be ideas of perception. 7. Others have divided our ideas into thofe ot memory, and thefe of imagination ; they have faid that a recollection of ideas, in the order they were received, conftitutes memory, and with- out that order, imagination ; but all die ideas of unagination, except Sect. XV. 2. CLASSES OF IDEAS. -93 except the few that are termed fimple ideas, are parts of trains or tribes in the order they were received; as, if I think of a fphinx, or a griffin, the fair face, bofom, wings, claws, tail, are all complex ideas in the order they were received; and it behoves the writers, who adhere to this definition, to determine how fmall the trains muft be, that fhall be called imagination, and how great thofe which fhall becalled memory. Others have thought that the ideas of memory have a greater vivacity than thofe of imagination ; but the ideas of a perfon in fleep, or in a waking reverie, where the trains connedied with fenfation are uninterrupted, are more vivid and diftindt than thofe of memory, fo that they cannot be diftinguifhed by this criterion. The very ingenious author of the Elements of Criticifm has defcribed what he conceives to be a fpecies - of memory, and calls it ideal prefence; but fire inftances he produces are the reveries of fenfation, and are, therefore, in truth, connec- tions of the imagination, though they are recalled in the order they were received. The ideas connected by afTociafion are, in common dif- courfe, attributed to memory, as we talk of memorandum- rings, and tie a knot on our handkerchiefs to bring fomething Into our minds at a diftance of time. And a fchool-boy, who can repeat a thoufand unmeaning lines in Lilly’s Grammar, is faid to have a good memory. But thefe have been already fhewn to belong to the clafs of affociatian, and are termed ideas of fuggeition. II. Laftly, the method already explained, of claffing ideas into thofe excited by irritation, fenfation, volition, or affocia- tron, we hope will be found more convenient, both for explain- ing the operations of the mind, and for comparing them with thofe of the body ; and for the illuftration and the cure of the difeafes of both, and which we fhall here recapitulate. 1. Irritative ideas are thofe which are preceded by irrita- tion, which is excited by objeriis external to the organs of fenfe : as the idea of that tree, which either I attend to, or which I fhun in walking near it without attention. In the former cafe, it is termed perception, in the latter, it is termed limply an ir- ritative idea. * - 2. Senfitive ideas are thofe which are preceded by the fen- fation of pleafure or pain, as the ideas which conftitute our dreams or reveries : this is called imagination. 3. Voluntary ideas are thofe w'hich are preceded by volun- tary exertion, as when I repeat the alphabet backwards : this is called recolledtion. 4 . AfTociaty CLASSES OF IDEAS. 94 Sect. XV. 3. 4. AITociate ideas are thofe which are preceded by other ideas, or mufcular motions, as when we think over or repeat the alphabet by rote in its ufual order, or fing a tone we are accuftomed to : this is called fuggeftion. IIL 1. Perceptions fignify thofe ideas which are preceded by irritation, and fucceeded by the fenfation of pleafure or pain ; for whatever excites our attention interefls us ; that is, it is accompanied with pleafure or pain, however flight may be the degree or quantity of either of them. The word memory includes two clafles of ideas, either thofe which are preceded by voluntary exertion, or thofe which are fuggefted by their aflbciations with other ideas. 2. Reafoning is that operation of the fenforium by which we excite two or more tribes of ideas, and then re-excite the ideas in which they differ, or correfpond. If we determine this difference, it is called judgment ; if we in vain endeavour to determine it, it is called doubting. If we re-excite the ideas in which they differ, it is called diftinguilhing. If we re-excite thofe in which they correfpond, it is called comparing. 3. Invention is an operation of the fenforium, by which we voluntarily continue to excite one train of ideas ; fuppofe the deflgn of raifing water by a machine ; and at the fame time attend to all other ideas which are connected with this by eve- ry kind of catenation, and combine or feparate them volunta- rily for the purpofe of obtaining fome end. For we can create nothing new, we can only combine or fe- parate tiie ideas which we have already received by our per- ceptions: thus, if I wifh to reprefent a monfter, I call to my mind the ideas of every thing difagreeable and horrible, and combine the na^linefs and gluttony of a hog, the ftupidity and obftinacy of an afs, with the fur and awkwardnefs of a bear, and call the new 7 combination Caliban. Yet fuch a monfter may exift in nature, as all his attributes are parts of nature. So, when I wifii to reprefent every thing that is excellent and ami- able; when I combine benevolence with cheerfulneis, wifdom, knowledge, tafte, wit, beauty of perfon, and elegance of man- ners, and affociate them in one lady, as a pattern to the w 7 orld, it is called invention ; yet fuch a perfon may exift, — fuch a perfon does exift ! — It is , who is as much a mon- fter as Caliban. 4. In relpedt. to ccnfcioufnefs, we are only confcious of our exiftence when we think about it; as we only perceive the lapfe of time when w T e attend to it ; when we are bulled about other objects, neither the lapfe of the time, nor thecon- fcioufnef* CLASSES OF IDEAS. Sect. XV. 3. 95 fcioufnefs of our own exiftence, can occupy our attention. Hence, when we think of our own exiftence, we only excite abftradted or reflex ideas (as they are termed) of our principal pleafures or pains, of our defires or avarfions, or of the figure, folidity, colour, or other properties of our bodies, and call that act of the fenforium a confcioufnefs of our exiftence. Some philofopher, I believe it is Des Cartes, has laid, “ I think, therefore I exift.” But this is not right reafoning, becaufe thinking is a mode of exiftence; and it is thence only faying, “ I exift, therefore I exift.” For there are three modes of exiftence, or in the language of grammarians, three kinds of verbs. Firft, fimply, I am, or exift. Secondly, I am acting, or exift in a flate of activity, as I move. Thirdly, I am fuf- fering, or exift in a ftate of being adted upon, as I am moved. The when, and the where, as applicable to this exiftence, de- pends on the lucceffive motions of our own or of other bodies, and on their refpedtive fttuations, asfpoken of, Se6t. XIV. 2. 5. 5. Our identity is known by our acquired habits, or catenat- ed trains of ideas and mufcular motions ; and, perhaps, when we compare infancy with old age, infthofe alone can our iden- tity be fuppofed to exift. For what elfe is there of fimilitude between the firft fpeck of living entity and the mature man ? Every dedudfion of reafoning, every fentiment or paflion, with every fibre of the corporeal part of our fyftem, has been fub- jedf almoft to annual mutation ; while fome catenations alone of our ideas and mufcular adtions, have continued in part un- changed. By the facility with which we can, in our waking hours, voluntarily produce certain fucceffive trains of ideas, we know by experience, that we have before re-produced them ; that is, we are confcious of a time of our exiftence, previous to the prefent time ; that is, of our identity now and heretofore. It is thefe habits of adtion, thefe catenations of ideas and mufcular motion, which begin with life, and only terminate with it; and which we can in fome meafure deliver to our pofterity, as ex- plained in Sea. XXXIX. 6. When the progreffive motions of external bodies make a part of our prelent catenation of ideas, we attend to the lapfe of time, which appears the longer the more frequently we thus attend to it ; as when we expea fomething at a certain how, which much interefts us, whether it be an agreeable or difagreeable event, or when we count the palling feconds on a ftop-watch, - When an idea of our own perfon, or a reflex idea of our pleafures and pains, defires and averfions, makes a part of this catenation, OF INSTINCT. Sect. XVI. .96 catenation, it is termed confcioufnefs ; and if this idea of con- 'feioufnefs make a part of a catenation, which wc excite by recolledtion. and know by the facility with which we excite it, that we have before experienced it, it is called identity, as ex- plained above. 7. In refpedl to free-will, it is certain, that we cannot will to think of a jiew train of ideas, without previoufly thinking of the hrft link of it; as I cannot will to think of a black fwan without previoufly thinking of a .black fwan. But, if I now think of a tail, I can voluntarily recollect ail animals which have tails; my will is fo tar free, that lean purfue the ideas linked to this idea at tail, as far as my knowledge of the fubjedt extends ; but to will without motive is to will without deGre or averfion, which is as abfurd as to feel without plea- sure or pain ; they are both foiefcifms in the terms. So far are we governed by the catenations of motions, which affect both the body and the mind of man, and which begin with our ir- ritability, and end with it. SECT. XVI. OF INSTINCT. Haud equidem credo, quia sitdivinitus illis Ingeuium, aut rerum fato prudentia major. Virg. Georg. L. I. 41 5. I. Inf in Clive anions defined. Of connate pajfons. II. Of the fenfations and motions of the foetus in the womb. ill. Some animals are more perfectly formed than others before nativity. Of learning to walk. IV. Of the /wal- lowing, breathing , fucking, pecking, and lapping of young animals. V. Of the fenfe of [me If and its ufes to ani- mals. Why cats do not eat their kittens. W. Of the accuracy of fght in mankind , and their fenfe of beauty. Of the fenfe of touch in elephants , monkies , beavers , men. VII. Of natural language. VIII. The origin of natural language: 1. The language of fear ; 2. of grief ; 3. of tender pie a fur c ; 4. of ferene pleafurc ; 5. of anger ; 6. cf attention. IX. Artificial language of turkies, hens, ducklings , wagtails, cuckoos, rabbits, dogs and nightin- gales. X. Of mufc\ of tooth-edge ; of a good ear; of architecture. XI. Of acquired knowledge ; of foxes, rooks, fieldfares , lapwings, dogs, cats, horfes, crows and pelicans. XII. Of birds of paffage, dormice, fnakes, bats, j wallows , quails,, ringdoves, fare, chaffinch , hoopoe, chat- terer. Sect. XVI. i. OF INSTINCT. 97 terer, hem finch, erofsbill, rails , and cranes. XIII. Of birds’ nefls ; of the cuckoo ; of f wallows’ nefs ; of the /m- lor bird. XIV. 0/~ t/ze o/