The economy of the animal kingdom, considered anatomically, physically, and philosophically

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cation, r What is more agreeable than the society of the Muses When they prosper Our endeavors,) clearly to elucidato the sortiis Of the respective actions of the body ns determinod by tho influxos the nerves n. 473).509. Let the causes be given then, and we may rendi ly COH- clude What are the effecis produced in the muscies, What is theextension of their motion, What iis duration, What iis degree, What iis celeri ty, What iis determination Dom One potui tonnother; for these particulars floW nil as determinate conSequents according to the acting causes. Is they floW DOm auinternat cause, or Dom the brain, then in this case, I. Such asis the extent of the portion os cortical substance that animates particularly, Such is the extent of the action resulting upon thenerves and Voluntary muscies dependent upon them. Whencethe disposition os the cortical tori, and the connection Os the fascicles proceeding Dom them, exhibit the most ingenious arra gement. It is for this reason, moreOVer, that motion can bepersormed more quickly Or StoWly, and more Strongly or feebly, Or Within a more extended or more confined Space, according totho mill of tho determining poWer. 2. Is they floW Dom an externat cause Or froin the body, then in proportion as thenervous fissue is extended, vibrated, irritated, or affected in any Other manner Suit te to it, in the fame proportion are thequantity and quality of the action Whicli sollows. 3. All othorphenomena produced by externat causes are regulaten accordirigio tho disposition, determination and condition of the fibres; as, sor instance, according to those of the nervous fibres, thos also of the white motive si bres, and those of the Sanguineous Orfleshy motivo fibres; for thus it is that the muscie, Whicli is a compound of iis OWΠ sibres, is excited, disposed, and determinedio action. Τhe phen Omena are regulated also according to thesiluation and form os the motive fibres in relation to their ten- dotis Or extremities, and of these to the cartilages, bones ormoveable potnis, the action of Whicli is intended as the last determined action; they are regulated also according to the dependence of One muscle upon another. All of Which boingmost Wondersul determinations Os nature acting, and these determinations being also mechanical, sor fibres of every Orderrepresent 1 Orces and poWerS, RS in machines,) cannot be explained

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in a seW WOrds, hecause there is noWhere throughout the body a Single nervous fibre, a single motive fibre or muscie, Whicli actS, floWs, and is determined in a mauuer similar to an Other. HeneeeVen to assign the generat laWs of motion is a lassi os immense

labor; to potnt out, there re, iis various particular laWs must beto dissert separalely upon ali the acting potnis in the body, notonly in the human, but in that of every individual animal; consequently it Would be to assign as many ratios as are to he found in the whole compass Os arithmetic, geometry, mechanicS, Phy- Sies, and the algebraical calculus; and yet notWithstanding allthis, there is not a single laW Which may nos be Dund Whenthe causes and effecis are given and their intermediates dulyinvestigated. Ou the subject of the causes Os muscular motion, thallearned and experienced anatomist Winstos has the followingobservations : The particular mechanism and immediate cause of muscular action has much pugZled the Wits of numerous physiologisis. The extreme delicaoy of the texture of a movingsibre, and a great number of phenomena, Some of them Very obvious, Which have not been attended to, have hitherio pre- vented the discovery of the mystery. Severat hypotheses have been formed respecting the structure of this fibre, Whicli . . . haS been Supposed Spongy, VRScular, Vesicular, contorted, elaStic, c., and various ideas have prevallest With respect to the concurretice of disserent fluids With the supposed structure of thesbre. And systems have even beeu founded Wholly on thespring or elasticity of the solid or firm paris of Whicli a muscleis composed. But On considering attentively the phenomena Riready mentioned, ... est these different systems sali to thoground. For hitherio no instance can be Dund, either in natureor Rrt, of any explosion, fermentation, ebullition, injection, insation, imbibition, vibration, elasticity, kc., by Which We cauregulate and determine to a gi ven degree the Space, Velocity, and duration of any artificiat motion, or by Which We caii begiuand put an end to suci, motions in au instant of time at Our pleasure. It is there re to no purpOSe to amuse Ourselves With What has been suid upon this subjeci: another method must befollowed, Whicli consisis in collecting and examining est the facts avd phenomena that can fali under our observation. Τill some

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such luchy discovery is made, What cari hitherio With tho groatost certainty be gathered from the Structure, conformation and action of the muscies, is, that their strengili deponds on thonumber of their fleshy sibres, and the quantity and extent of thoir motion, On the tength of these fibres. For Wherever

Wo snd tho fibres multiplied in proportion, and the space theyocciapy is skilfully economiged by the oblique disposition os themiaready mentioned. In like manner Whereuer there is greater

conveyed doWΠWards, sumped upWardS, and 8O circulated, paSSeS for the most part through the periostea into the vaginat tunic offlio spinal marroW, and thetice into each periosteum os thecranium, namely, the internat Or dura mater, and the externat. 5II. We should also add, that Whilo the animation of thebrains coincides With the motion of the heari, as in the foetus besore birili, no muscular motion can be produced in the bodyexcepi that of the heari, arteries and vetiis. In these there isno Other species of motion thau the most common and universat,

that is to say, no Other than the animation of the brains, With Whicli at that timo tho motion of tho hoari coincides. For this reason ali the nervous fibres at this period aci alternately Withthe blood, so that Whon a fibro opens the pores of a muscle, theblood flows tuto them, and vice versa; againSt thi8 generat cur-

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rent, Whicli is renovated both Dom tho braitis and D m thelieari, no fibre or cortical torus can riso or elevate itself. This

be constricted by itself, or risu separately, the entire current Would resist it, Dot Only tho current in the fibros, but also that in the vesseis, for it Would bo attendod With a loss of the suc- COSSive circulation. As soon there re as this bogitis to tu heslRCO, Or RS SOOn ns the muscies attempt to aut individually, thochange Whioli arises incites tho foetus to pass Dom the WOmbinto the open uir, in Ordor that the circulation may be inverted With sufety, through the medium of the lungs. When this inversion of the circulation is accomptished, and the animation Ostho bra in is no longer synchronous With the pulsation Os thelieari, and When every particular res Weli as generat animationsonds the blood domu froni tho motivo fibres of the muscies into the vena cava, then the fibro is able to aut against the bl ood, and the bl od against the fibre, tho internat cause against theexternat, and the externat against the internat, and each viscus respectively is excited to motions corresponding in character totis acting CRUSOS.

With these principies, let us proceod lo investigate the proximate and remote causes of the motion of the heart. 512. Affer a due consideration of these subjecis, we 8haulearn, thul the proiimate cause of the heari's diastole, is the continuat pressure and action of the blood of the two venae cavoe et Onthe risthi auricle; and that the promimate cause of the hearl'S Sy8tole is the extension of the nervous sibi es: so that when the blooducis, the nervous sibi e yieliis; and when the nervous Abre acis, the

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blood yieliis. For the salie of inexperieticod reudors, I Will firstos ali givo a stiori account of the alternate motion os the auricles and ventricles; and as Boerhaave supplies us With one Whicli is very clear and succinet, it Will be sussicioni to cito his Woriis. Both the venous sinuses,V says he, are filled, turgid, and red, at one and the fame time; and so are both tho auricles. Both the auricles become flaccid at the fame instant,aud so also do both the venous sinuses. At the Very moment

tho impulse of that in the vetus, and by the contractile actionos the aloining muscular venous sinus. At the Same instant, both ventricies contraci, are empti ed Os blood, become pale, and the two great arteries aro siled and dilated. At the moment aster this constriction, euch empty ventricle is flaccid, elongated, and reddened, and iis cavi ty enlarged. Scarcely hasthis happened, When both auricles, and both muscular Venous SinuSes, contraet With a muscular motion, express the blood they contain, and propel it into the ventricles; and noW tho auricles become pale n. 460, p. 429). Thus the motion of tho auricles and ventricles is alternate; so that When the auriclesare compressed and emptied, the ventricles are silled With bloodand expanded, and vice versa. It is likeWise to be observed, that as soon as the auricles are silled and expanded, the two arteries, Vig., the pulmonary artery and the norin, are also expanded, so that the Whole sanguineous SyStem depending uponthem comes into a state os dilatation in conceri With the auricles, the ventricles alone at this time being compressed. Forthe Sine of a clearer apprehension of the subject, I Will Witti Lancisi cali the largor belly of the auricle iis caudex, Or With Boerlinave term it the venous sinus: but Where this part is contiguous to the vena cava, I Would cali it the vestibule or uppervavit, for it is hom this potnt that it enlarges into a sinus. Butthe auricle strictly is that fimbriated part that projecis beyonditio base of the heari, and Drms a fringed border, and as it Were a pectinated crest. But as these particulars belong merolyto the science of anatomy, I shali not any longer delain theroader On this part of the subjeci, but immediately procoed toelucidato the cause of this alternate constriction and expansion. 513. Τhat the sole proximate cause of the eXpansion Os the

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alaricles, is the pressuro and action os tho blood os tho vena cava in the vestibulo or first entrance into the auricular Sinus orcaudex, is abundantly proved by experimens. In the vivi section Os foWls,V says Lancisi, Wo saW a vermicular motion in the branches of the cava frequently recurring, solioWed ut tengthby a StoW contraction, or fluctuation, Os the ample right auricle

pulse in the lust auricio; and whon tho test ventricio Was laidhach, We could observe no motion in iis posterior Wali; althoughthe segments of the hoari moved When punctured With a noedle; a Sufficient proo that the occasiones cause as they say) os Spontaneous tension in the right auricle and ventricte, consisted in the poWersul pressure of the blood, Whicli vas urged tOWardsilio right chambers of the hestri by the branches of the cava peristallicatly contractingV n. 465). And Steno says : Whenthe three branches of the cava wero fled, and ali tho blood that was With in the ligature, in the cava and right auricle and Ventriclo, Was let Out through a litile opening made With a finenoedio in the bottom of the right ventricte, ali motion censed at Onee, and One Would have suid that the whole of the paris Wore dead. Diat this state os rest did not continuo long, since thesresti blood issuod Dom the vetiis of the heari, and stlotly distending the collapsed tunius, producen a fresti but stight mo

theleSS, When the ligatures Wore removed, and the blood couldfreely return to the hemi, the motion Os both the cava undaurietes Was restored immediatelyV n. 466 . That tho sole proximate cause of the expansion Os the auricles, is the pressureand action of tho blood of the vena cava in the vestibule or sirsten try in to the auricular sinus, hecomes stili more Clear, When We considor that the motion of the heari can be resuscitatedaster death by injecting oither blood Or Warm Water into the Venn Cavn, Or into the subclavi an or jugular vetus n. 467). Fromthese Vari Ous circumstances, Lancisi comes to the folloWing conclusion. Since it appears DOm experiment, When the ligatures ΟΠ the Vena cava are IOOsened, and the blood consequently 1lowsthrough the usual channot into the right auricle and ventricte, that the motion returus spontaneousty to the cavities of thelieari; While on the contrary, When the blood is stagnant in the

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pulmonary vein and lest auricle, in cΟΠSequence of the suspension of respiration, that the motion of the lest auriclo, unda largo part of the lest Ventricte, immediately dies; me maymost unhesitatingly conclude, that the blood is the proximato cause of the pulse of the heart. But on this fertile subject, letus come to R Ahori Statement, and content Ourselves vitii declar-ing, that tWo principat things are necessary to the natural mOtion of the hestri, namely, the action of the nerves, and theaetion of tho blood V De Motu Cordis, &c., lib. i., prop. 56.)514. The manner in Whicli the venous blood, simply by iis pressure and action, is enabled to Occasion these alternati gmotions, is purely mechanicat, the nerves producing the essectby their alternate relaxation aud constriction. Nothing is more common in mechanicia experienee, When ulternate motions areto be produced, than the employment of a single force actingwith the most perfeci constancy. Τhus in the caSe of automa-tonS, We HSe the Spring or pendulum ; in machines of othorkinds, the wheel or levor, Whether turned by Water, Wind, catile, Or any Other poWer. The motion Of this produces that of thoother paris of the machinery, and thus through the medium os pulleyS, WheelS, IeVers, ke., We cause reciprocul actions of thooriginal moving poWer. With ingenuity much greater, thesume thing is essected in the machinery of the hears, Where numerous fibres are arranged With ali the scienco and skill os nature, and receive their animation DOm the bratiis accordingto this arrangement; for the more numerous, the SOunder and the purer they are, the better and more distinet is their modoos acting, and the more Sure they are os producing the required effeci, as me find to be the case during youth; for to the endthat they may readily folloW each Other in duo mechanical Order, they are So compounded, that iapon the action os any giveri cause, every fibre, and particularly that Whicli is dopondent upon the par Vagum, SpontaneouSty rusties into such conditions as are ad ted to ensure the conservation Os the viscus, and the administration of the natural Osfices. Henee this machino is eastly brought into the discliarge Os iis alternate functions, lar We learn DOm experieuce that the contact of a Warmbody,-the breatli, the application os saliva on the fingers, os the potui os a pen, and Such like,-restore the Whole machino

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to iis motion. The ouly requisite there re to produce this alternate motion, is a pressing or acting sorde in the vestibule orthreshold of the vena cava at the auriclo, that is to SV, the Veii0us blood, Whicli attempting to soW into the nuricle, RS SOonas enough is supplied for the influx, may excito the heari to iis natural and alternate motion, and cause the diastole of the auricle, Dom Whicli the systole of the ventricles necessarily DJ

515. But be re Wo attempt to explain to the reader themode in Whicli this is dono, it Will bu necessary sor him to familiarigo himself With tho accompanying plate DOm VieuSSenS,aud to stud y it Weli upon the principies We have bo re premised reSpeeting the causes of muscular motion n. 508, 509 . AndWe are to Observe, that this plate represenis the Derves thatenter the substance of the heari; for as the author implies, theyare Seen When the anterior region of the heari is denuded of thoperi cardium and sanguiferous ducis. Seu the Ρlate, Κ.J Butilio nervos delinented by Lancisi, De Motu Cordi8, tab. i., i V., Vii., are those that more especialty Occiapy the sursace, and ensold the

scend along the ouisi de of the pulmonary artery; but thosethat are distributed over the posterior Sursaee, run at the Sideos the uortin n. 463, p. 435 . See n. 501. Let us then confine our attention to the plate Os Vieussens, in Which We are tonotice, that at the vestibule of each auricle, or at the place

Where the vena cava passes into the right auricle, and the pulmonary veiti into the lest, there are nervous ringS Or girthS represented in the plate by figures 12, 12, 12, 3, 4, stom Which