Columbia itotoetaitp mtljeCitpoflrtugork College of $jjpgictang anb iburfleong JLibvavv Digitized by the Internet Archive in 2011 with funding from Open Knowledge Commons http://www.archive.org/details/inauguraldissertOOpost A N INAUGURAL DISSERTATION, TO DISPROVE THE EXISTENCE OF MUSCULAR FIBRES IN. THE VESSELS. SUBMITTED TO THE PUBLIC EXAMINATION OF THE FACULTY OF PHYSIC, UNDER THE AUTHORITY OF THE TRUSTEES OF COLUMBIA COLLEGE IN THE STATE OF NEW-YORK: WILLIAM SAMUEL JOHNSON, LL.D. Prefident; FOR THE DEGREE OF DOCTOR OF PH.rSICi ON THE THIRTIETH DAY OF APRIL, 1 793" By JO TH AM POST, A. B. Citizen of the State of New-York. CRIMINOSA EST CELERITAS IN JUDICANDO. NEW-YORK: Printed by T. and J. Swords, Printers to the Faculty of Phyfic of Columbia College. • — 1793.— ■ *Vd G&'&B imprimatur, Samuel L* MitchilL RICHARD BAYLEY, Profeflbr of Anatomy, AND WRIGHT POST, ProfeiTor of Surgery, IN COLUMBIA COLLEGE: Grateful Teflimony for their Care and Attention to him, in his Medical Studies, THIS DISSERTATION IS ADDRESSED, By their Pupil, The AUTHOR, A N INAUGURAL DISSERTATION, &c. O I N C E the difcovery of the circulation of the blood, the attention of Phyfiologifts has been excited to afcertain the manner in which it is carried on. The heart is univerfally allowed to be the principal moving power; but many fuppofing it incapable, of itfelf, of propelling the blood through the fyftem, have conjectured means, by which its aclion might be affiHed, and the routine of the circulation facili- tated. They have fuppofed the vefTels of the fan- guiferous fyftem to be encircled by mufcular fibres, which have an alternate contraction and dilatation, by which an additional power is obtained for keep- ing up and carrying on the circulation. An examination of this fubjed is of more import- ance than might at firft be imagined ; for upon a fup- pofition of the exigence of mufcular fibres in the ar* teries, has been founded an opinion, which is now becoming very general, of the proximate caufe of B many C 6 ) many important diieafes.* It is true, fuch an opinion^ at firft. view, exhibits fome degree of plaufibility ; but upon more accurate invertigation, it appears to be rather the creature of imagination, than the refult of impartial obfervatiph and deliberate reafoning. Many eminent characters have made experiments to afcertain the projectile force of the heart-f , fome cf which have made it almoft, inconceivably great, while others have confined it to a fmaller compafs. But however they may differ, it is ftill proved be- yond a doubt, that its rtrengthi is confiderable, and to thofe who are willing to be unbiased by pre- pofleiTed opinions, furTicient to propel the blood through every minute ramification of the arteries, and veins, independent of their mufcular power, ad- mitting fuch. Why then mould we fly to the aid of a caufe, the affiftance of which is not at all requifite ? The opinion, that mufcular fibres encircling the veffels are necerTary for the circulation, moft pro- bably muft have originated from conjecture. But conjecture, * Among thefe, fevers and inflammations hold no inconsiderable rank. See Cullen's Firft Lines, volume firft, fabjecT: pyrexia;. See Bell and .Cullen on the proximate caufe of inflammation. ■f See Kales's Hsemaftaticks. See Keil's Anatomy, and Calculations on the Force of the Heart, &c. X By the words strength and power, which are uled throughout: this Treatife, I would not wifli to be underftood to mean any great cxcr- tica. The terms are ufed fcr want- of moreexpreliive ones. ( 7 ) conjecture, though fometimes of ufe to the ingeni- ous in the difcovery of truth, unlefs well fupported by fact, fhould never be miftaken for demonftration. The learned Hailer,* who has applied much care, and attention to the investigation of phyfiologicai fubjects, fuppofed the exiftence of mufcular fibres in the vefTels as requifite to affift in carrying on the cir- culation, yet exprefsly declares that he never could detect any mufcular fibres, nor perceive any con- traction, in the arteries, though he had ufed micro- fcopic inftruments for that purpofe. This is a fingu- lar inftance of prejudice, to affert the efientiality, and believe the exiftence of mufcular fibres in the vefTels, as requiflte for carrying on the circulation, though unsupported, and in a manner contradicted by his ov/n experiments. But what may we not expect from refearches made to Support a favourite hypo- thefts ! If, from the prefence of mufcular fibres on the aortaf near its origin from the heart, we infer their exiftence throughout the fyftem of circulation, we may commit an error; for whenever we meet with them there, which, in fact, is but a rare occurrence, they * Vide e*p*r:rrv;nta de irritabiiitate, feci. 2d. -j- Becanfe in fame inftances they have been fctn on the aor'o, the cr- jftence of mufcular fibres by analogy has bten inferred throughout ye pf the circulating fyftem, ( 8 ) they are moft probably the confequence of forne morbid affection. I am confirmed in this opinion from the following circumftance. There is in the Anatomical Mufeum of Columbia College, a prepa- ration of an aorta, with an incurvated fpine. The aorta, juft below its curvature, has become fo much enlarged as to form a complete aneurifmal fac. Round this fac, and the parts adjacent to it, there was a num- bur of mufcular fibres plainly vifible to the naked eye. But inftead of forming the middle coat of the aorta, as is generally imagined and aflerted, they were external to the common loofe cellular coat of the artery, and had very little connection with each other. Neither did thofe which were on the aorta wholly embrace it. The part moft remote from the difeafe, had not the leaft appearance of them. From this, and from fimilar cafes, as well as from the fad, that, in fubjects really found, thefe fibres are not to be difcovered, we may conclude, that they only exift as the confequence of difeafe. For no Phyfiologirl: will deny, that mufcular fibres, or at lead what appear to be fuch, may arife from the morbid affection of membranous parts. I have repeatedly examined the aortas of oxen, fneep, and other animals, as well as of human fub- jects •, but have never, while in a found rtate, been able to difcover the leaft veftrge of mufcular fibres in them. Upon ( 9 3 Upon the fuppofition of the exiflence of mufcular fibres in the veffels, as efTential to the circulation, and anincreafe of their influence as they recede from the heart, I fuppofed they might be found in the iliac arteries, but when I examined thefe, not the fmalleft appearance could be obferved to juflify the opinion. However, fuppofmg I was not far enough diftant from the heart, I imagined they might be- come more evident in the tibial and fmaller arteries, which could be eaflly feen \ for, according to the ad- vocates for mufcular power in the veffels, thefe are iefs under the influence of the heart, and of courfe, the prefence and action of this power become more requifite: but here again, upon examination, not the leaft appearance of mufcular fibres could be dis- covered. Unwilling, however, to relinquifh the idea, from its being fo very generally believed, that there was a fyftole and diaftok in the arteries, becaufe I could not difcover the prefence of mufcular fibres in them with the naked eye, I fuppofed they might be fo fmall as to elude the fight, and that their contraction and dila- tation would become evident by their effects. I ac- cordingly attended to the flowing of blood from the carotid arteries of animals ; but could not obferve any fenfible alteration in the ftream as it ifTued from their mouths, any farther than that it came forth ( io ) forth with an increafed or diminifhed velocity, as the heart contracted or dilated. The diameter of the ftream apparently remained the fame while the vefTels were in a ftate of distention -, nor did the fides of the vefTels approach each other. This coincides with Doctor Kirkland's* obfervation, that " fo far are the larger arteries from becoming wider or narrower al- ternately, that their rides have not the leafb motion of this kind, whether the blood flows freely through them., or whether it is interrupted at the extremity of the divided vefTel ; which experiment we made to prevent our being miftaken, by any alteration that might take place from the refinance to the blood be- ing entirely removed; but the fides of the vefTels w r ere greatly diftended, yet they were perfectly ftill and quiet." Inftead, therefore, of concluding that the vefTels of the fanguiferous fyftem are encircled with mufcular fibres to afTift in the circulation, we are induced to adopt a contrary belief If the arteries have mufcular fibres, and are of courfe irritable, they would, before life itfelf becomes extinct, fliew fome figns of it, when put to the teft of experiment. But this, however, did not appear; for, having taken a carotid artery from an ex imme- diately after his throat was cut, I threw into it fome water, * See Kirk! and'5 Medlca-Chirurgical Treatife* volume the £rl, pa^e 309, ( II ) water, about the temperature of the blood, but could not obferve the leaft contraction in it, urdefs when diftended \ and then, by means of the elaftic membranes of which it was formed, part of the water would pafs out. I am informed, that an experiment of this kind has been confidered abfolutely conclu- five of the exiftence of mufcular fibres in the fangui- ferous fyftem as efTential to the circulation of the blood. The conclufion, however, muft have been haftily made ; for any perfon, who has impartially and carefully attended to the experiment, might have been convinced, that the arteries were elaftic tubes, and of confequence, if put upon the flretch, mud necefTarily contract, and force out the fluid from within, as if by a mufcular contraction ; and the ve- locity of the fluid ruining out would be nearly pro- portionate to the diftention made. In order farther to illuflrate the truth of the opi- nion, that the aid of mufcular fibres encircling the vefTels of the fanguiferous fyftem is in no wife requi- fite, or efTential to the circulation, I laid bare the carotid artery of an ox immediately after his throat was cut, and tied it in two feparate places, that be- tween the ligatures the artery might be filled with blood. I then punctured it with a lancet, when the blood, inftead of being forced out by a contractile and dilating power, as it rnuft have done if mufcular agency ( 12 ) agency had been the caufe, regularly trickled down the fides of the vefiel. The artery, however, was not much diftended -, otherwife, from the re-action of the elaftic power, I fuppofe the blood would at fir ft have iffued out in a flream. At the Anatomical Theatre of Columbia College I have (cm Profefibr Bayley lay bare the carotid ar- tery of a dog, nearly three inches in length, in order to afcertain whether it would contract or not. We examined it with clofe attention, but could not per- ceive any motion in it, either of contraction or dila- tation.* This, too, perfectly agrees with what Hal- ler himfelf obferves •, " for upon examining the cir- culation in animals with a microfcope, I have never obferved any contraction in the arteries. I have viewed the circulation for whole hours in Mies and frogs, and during the whole time the rides of the vefTels remained as quiet as thofe of the tube with which I examined them." Doctor Kirkland's ex- periments on the fame fubject coincide with thofe of Haller.f So far experiments feem directly conclusive, that the arteries and veins, excepting their elafticity, are paffive conductors to their contained fluids. Obser- vation * The pulfe, however, was plainly felt at every contra&ion of the heart, f See Kkkland's Medico-Chirurgkal Enquiry, volume firft, page 310. ( i3 ) vation and reafon may afford us many more argu- ments to confirm the opinion, From the ftrudture of the heart, we may draw very forcible reafons, to induce us to believe, that the arteries and veins afford no other affiflance in the circulation, than that which ariies from their elas- ticity. The right ventricle, compared with the left, has but very little Strength. It has not to fend the blood fo great a diftance, nor through fo complicat- ed a courfe, and therefore fo much ftrength is not neceffary. But the left ventricle, which has to pro- pel the blood through the moil diftant parts of the body, as well as thofe which are lefs remote, has its power proportionably greater. Does not this great -disproportion in the ftrength of the ventricles afford us a ftriking argument in favour of the opi- .nion, that Nature has placed in the heart the Sepa- rate power of carrying on the circulation ? If the arteries and veins are endowed with a power for carrying forward their own contents, why the neceftity of a heart endowed with fo much mufcular force ? or, indeed, why the neceftity of a heart at all? Let the blood be but placed in the arteries and veins, and they of themfelves would be capa- citated to keep up the circulation. C Had ( 14 ) Had the arteries been originally derlgned to have had a contractile and dilating power from the influ- ence of mufcular fibres encircling them, fome more convenient method might have been taken to bring them into action. We cannot fuppofe that Nature, ever regular and fimple, would perform her func- tions by indirect, and complicated means in man, her favourite, efpecially where complication appears entirely unnecefTary. But this would evidently ap- pear to have been the cafe, mould we allow the ex- igence of mufcular fibres in the veilels \ for between the coat which is faid to be mufcular, and the blood Vv r hich is to excite it into action, is interpofed a firm denfe membrane.* Membranes, in a found ftate, fire infenfible:-}- Therefore, if the arteries have muf- cular fibres feparated by this infenfible body from the blood which is to act upon them, they cannot be brought into action by any direct means ; and to fup- pofe that Nature ever defigned much farther aflift- ance in the circulation, than that which arifes from the heart, connected with the elafticity of the vef- fels, is detracting from her perfections. If farther afliftance was requifite, why were not the veffels made into hollow mufcles ? Nature * See Haller's Firft Lines, feftlon 3 1 . See Falconar's Synopfis, page 1 6. •f Noted from Profeflbr Bayley's le&ureon membranes, and membra- nous parts. ( *S ) Nature is invariably the fame in her different Se- cies of creation ; and hence, if mufcular fibres have been {qqr in the veffels of one animal in a natural ftate, it is prefumable that they would be demon - Arable in another of the fame fpecies, which is con- tradictory to experience, On peruflng fome notes taken from Doctor Wil- liam Hunter's lectures in 1771, I rind that he does not admit of any other afliftance from the veffels of the fanguiferous fyftem, excepting their elafiicity, than as they ferve to conduct the blood to the vari- ous places to which it is deftined. He fuppofes the heart to be an agent in the circulation, and that in general it exercifes but little of its ftrength. However, he fuppofes what he calls nervous energy to have much influence, and that the circulation in ordi- nary cafes is almoft wholly carried on by it. The authority of fo great a man, in difcarding the idea of the exiitence of mufcular fibres in the veffels to affirt the circulation, mould have great weight ; for he never would have inculcated mch a doctrine, had he not been confirmed in it by actual obfervation and reafoning. Doctor Whytt,* who has written fo learnedly on the vital and involuntary motions, when fpeaking of the * See his Obfervations on the Vital and Involuntary Motions, fubjeft, fyftole and tfiaftole of the arteries. ( i6 ) the fyftole and diaftole of the arteries, attributes their contraction principally to their eiafticity. He appears to have adopted the notion of the prefence of mufcular fibres in them, only becaufe it had been fo generally believed,* without really enquiring into the merits or demerits of the hypothecs. Mr. Winflow, when fpeaking of the circulation of the blood through the liver, appears to have adopted the notion of the paffage of the blood through the vefTels without the aid of mufcular fibres ; for he obferves, that thofe " three kinds of venal blood-f meet in the trunk of the vena portse ventral is, where they are mixed together, and from thence they enter the tranfverfe finus or trunk of the vena porta? hepatica. In this finus they are ftill more intimately mixed, as . in a kind of lake, and become one uniform mafs of blood, which being forced into the branches of the vena portae hepatica only by the fupervening blood from the other vena portas, and by the lateral puhations of the ramifica- tions of the hepatic artery, its courfe mull be very fIow."j The * This is often the cafe, that becaufe an opinion is generally prevalent we readily fubfcribe to it, whether right or wrong. -j- The blood from the fpieen, pancreas, and inte>ftines, % The flownefs of the circulation here, however more probably, arifes frcm the greater capacity of the veins compared to the arteries, W ^ C H •carry blood to the abdominal vifcera. ( f* ) The manner in which the blood pafTes from the ventricles, and is received by the auricles, will alfo favour the idea, that the heart is the fimple engine for carrying on the circulation. Both ventricles con- tract, and both auricles dilate at the fame inftant^ and fo much blood as is fent from the former, is re- ceived by the latter. The reafon of this may ap- pear evident, when we confider that the arteries and. veins are in direct continuation, and considered as one continued tube, filled with a fluid which keeps them in a ftate of distention ; and therefore, what- ever caufe mould propel this fluid from the heart in the courfe of the arteries, will of neceflity caufe fo much as is propelled to pafs out of the veins. -J- Now, the ventricles propel - 3 and as much as triey propel, fo much the auricles receive. This procefs mufl continue, independent of mufcular afliftance from fibres furrounding the veflels to aid the cir- culation, as long as the heart is capable of continu- ing its action. J Since, * Utriufquc auricui* contf actio eodem tempore perficetur, relaxato tunc utroque ventriculo, et hi rurfus eodem tempore fe contrahunt auriculis iimul relaxatis. Vide Confpeft. Medicin. Theoret. audlore Jacobo Gregory, feclion 419. f Hence we may fee, why in aneurifms there Is an interrupted pulfe. X Wc may hence fee why, after blood has been drawn from the body, when there has been a great plethora, the pulfe becomes {0 much more full, free, and eafy, as the heart has a better opportunity of performing its office. C i8- ) Since, according to the mufcular hypothecs, fome other power is wanting befides the heart ; and fince an increafe of that power becomes more requifite in thofe parts which are more diftairt from the cen- ter of the circulation, the arteries, which are called capillary, mould be furnimed with mufcular fibres, which, did they exift, would be eafily demonftrable, and the veins, from an external view, would reprefent nothing but mere fiefhy cylinders. This, however, is contradicted by experience; for the coats of the capillary, or extreme arteries, are fo thin and delicate as to become perfectly tranfparent, and the veins, to appearance, are entirely deftitute of the leait veftige of mufcular fibres ; neither has demonftration ever proved the exiftence of mufcular fibres in them. If we admit the exiftence of mufcular fibres in the fanguiferous fyftem as requifite for the circula- tion, it cannot be readily conceived how the blood retains its progrefiive motion; nor can it be con ? ceived how mufcular fibres produce this effecT: : for if they are " actuated to their office by a ftimulus, they are incapable of being fuddenly lengthened by it, and being irritated, they inftantaneouily fhorten themfelves, and fpontaneoufiy return again to their natural ftate, when the irritating caufe ceafes to act."* They * See Kirkland's Medico-Chirurgical Enquiry, fubjedt, inflammation in general, pagez6o. ( i9 1 They are then as likely to repel, as to propel the blood. This moft probably would be the cafe, if the fibres contracted throughout the fyftem at the fame time •, for at every attempt made by the heart to fend forward the blood, the refinance would be proportionably increafed, becaufe the vefTels would become more full, and of courfe increafe the action of their mufcular fibres by its ftimulus ; and fo, in- ftead of allowing the vefTels to dilate, and the blood to be tranfmitted with greater eafe, they would lef- {en their diameters, and have a tendency to impede the circulation altogether. Neither can we fuppofe, that, if mufcular fibres are prefent, they perform their office by an undulatory or periftaltic motion, which, in fact, would be fomewhat the moft plaufible fiip- pofition, if we are allowed to reafon from analogy. Thus-the inteftinal tube, which has to convey its contents for different purpofes, is particularly notic- ed for its periftaltic motion, which may be eafily de- monftrated. But it has never yet appeared in the arteries > neither could it exift in them, unlefs the velocity of its motion was equal to that of the blood itfelf. But fuch a fuppofition is vague and hypo- thetical. I prefume, admitting its exiftence as a fact, fuch a motion might be difcovered by taking an ar- tery between the thumb and finger. I endeavoured to afcertain this by the experiment in which Profef- for C io ) ibr Bayley laid bare the carotid artery of the above mentioned dog, as well as in other instances, but did not fucceed. If mufcular fibres do really exift in the arteries toaffift m the circulation, their contraction and di- latation would ceafe when the nervous influence, which capacitated them for action, is taken away. It will be difficult then to conceive how the circula- tion is continued in paralytic cafes, particularly in the more general affections ; for in thefe, nervous energy is deftroyed almort throughout the body, and mufcular motion of courfe interrupted. It may be afked, then, why the heart continues its action ? why does it not partake of the general morbid af- fection ? The reafon is evident -, becaufe moft of its nerves arife directly from the brain; and therefore, while the brain is in any degree capable of perform- ing its function, the heart will continue its action.* Hence we may account for the almoft total tempo- rary fufpenfion of the vital powers in fyncope.-|- There * This vis infita of Haller may alfo have an aiding power. ■j I have been favoured with the following cafe, which will hereafter ■he publifhed more at large, and will have confiderable effect in confuting the idea of the prefence and action of mufcular fibres to aid the circula- tion. There is a man now living in this city, who fell head-foremoft from a load of hay, by which the weight of his body was loft on the bafis of the flcull. The fpinal marrow was concuffed j in confequence of which a very general paralyfls followed, attended with a difordered ftate of feveral of the fundVions. But notwithstanding this general affection la/led for fe- veral weeks* the circulation of the blood continued undifturbed. The ( 21 ) There is a wide difference between the ftructure of the heart and that of the blood-veffels ; and what brings the former into action cannot have the fame effect upon the latter. That the properties of the heart and arteries are different from each other, both before and after death, rauft be plainly vifible to any one who has attended to their appearances ; for the heart, like other mufcles of the body, when life be- comes extinct, remains foft and flaccid, while the arteries continue to retain their elasticity. They yield on the application of a diftending caufe, and refume their former ftate upon its removal. That the arteries alfo differ from the heart in a living ftate muft be evident, becaufe they appear not to be affect- ed by the fame caufes which affect other mufcles of the body. What foundation then can there be in the fuppofition, that the heart and arteries, fo dis- cordant in their nature, were deftined to perform fimilar offices ? Some fuppofe the coats of the arteries to be muf- cular, becaufe of their ftrength and thicknefs. This, however, molt probably arifes from the continued pulfation of the blood againft their fides, becaufe, in D infancy pulfe was as free and eafy as before the injury} and blood drawn from a Vein, flowed with its ufual celerity. In what manner could the circula- tion in this cafe have been aided by the acYion of mufcular fibres, which receive their influence from the nerves? The nerves were incapacitated for aclion,— Innumerable inftances of this kind could be given. ( 22 } infancy the coats of the arterial and venal fyftems are nearly of an equal thicknefs. But if mufcular fibres w the vefTels are really efTential to the circulation, the veins require them more than the arteries, fince they. are lefs under the influence of the heart ; and there- fore they mould have been thicker, which is con- trary to experience. When a degree of inanition is produced in the Pern, the arteries, from their elafticity, will con- trad: considerably, though they do not embrace the blood fo ftrongly as before. The circulation, how- ever, continues, which cannot be attributed to the action of mufcular fibres, even admitting their ex- igence in the veiTels •, for it is difficult to conceive how they poilefs the property of performing their office equally in one ftate of the arteries as in another. Yet fuch is the belief of fome who cannot relinquiirt a former opinion, too deeply rooted by prejudice, for one which is more plain, more characteristic of the fimplicity of nature. But it is the difpolition of man too often to grafp at things beyond the reach of comprehenfion, and to neglect thofe which might be plain and evident to his fenfes. We may be farther convinced, that the heart is the organ for carrying on the circulation, from the pulfe, which is always affected by thefmalleft altera- tion ( n ) tion produced in the action of the heart. Thus, if the pulfe be ftrong, we judge that the action of the heart is flrong : If the action of the heart be weak, the pulfe is weak ; if irregular, it is indicated by the pulfe ; and fhould its action ceafe altogether, the pulfe is no more. Further, although the action of the heart continues, mould there be a froppage made to the courfe of the blood in an artery, the pulfe is inftantaneoufly deftroyed. Thus, if prefiiire be made on the inguinal artery fufficient to flop the paflage of the blood ; at the inftant that it is {topped, the pulfe below is immediately deftroyed, and inflantly returns again when the prefTure is removed. Nov/, if there were mufcular fibres encircling the veffels, and having a command over them, we cannot ration- ally fuppofe that the flate of the pulfe would fo in- variably be regulated by the action of the heart. The phenomena which appear in a regular and un- interrupted circulation of the blood, may be imitat- ed by a hydraulic machine. Thus the common pump, for inftance, may reprefent the heart, and tubes leading from it, the arteries ; in which may be felt a pulfe, when the pump is in action, fimilar to that produced by the action of the heart itfelf. From the fact, that the arteries and veins are mere paflive conductors to their contained fluids, abftracting from their elafticity, we can eafily ex- plain, ( 24 J plain, why, when an animal dies from having its throat cut, and life itfelf becomes extinct, the blood {till continues to flow ^ for, from the elafticity of the veflels, their diameters will be continually leflening as the blood has an opportunity of efcaping •, and of courfe, until the arteries acquire their fmalleft dia- meters, the blood will be continually and regularly flowing through the given outlet. But if the blood gives a ftimulus to the veflels, and they are of courfe irritable from the mufcular fibres furrounding them, this appearance will never take place \ for as long as they contain blood, and continue irritable, it will be forced out in a greater or lefs quantity, as the fibres contract or dilate. If mufcular fibres were abfolutely neceffary to carry on the circulation, they muft of neceflity per- form their office by alternations of contraction and dilatation. The blood then, of confequence, fhould pafs out of every veflel, both vein and artery, per falium ; which is well known to be contradidted by experience : for the very minute branches of arteries, particularly thofe in the more remote parts of the body, when divided, will not pour out their blood at firft per faltum, but in one continued ftream, as we fhould a priori have fuppofed, from the idea that the veflels, abftracting from their elafticity, are paf- five conductors to their contained fluids \ but when the ( *5 ) the parts adjacent to the divided artery become fome- what emptied through the given outlet, the blood rufhes out per faltum, becaufe they become more full and turgid at every fy ftole of the heart. If there was a contraction and dilatation in the vefTels, it ihould become evident in the veins, as they are fo far diftant from the influence of the heart-, and, of neceility, the blood ihould pafs out in thefe per faltum. But the ap^ pearance of the blood iiTuing from the orifice of a vein in blood-letting, entirely contradicts this opinion.* Indeed, thefe two facts, that the blood iflues from the extreme arteries at firrt, and from the veins moil generally, in a continued ftream, might be confider- ed as abfolutely concluiive of the non-exiftence of mufcular fibres in the fyftem to aid the circulation ; for did they exilt, the blood muft always be forced out with an increafed or diminiihed velocity, accord- ing to their contraction or dilatation. So itrongly does common {m{c confirm us in the belief of elafticity in the arteries, that in common expreilions v/e are forced to mention it to exprefs or explain our ideas. Thus, the celebrated Doctor Cullen, who has taken fo much pains to maintain the idea of a fpafmodic affection of the extreme ar- teries * There may be inftances in which the blood will pafs out of the veins as if from arteries, as is fometimes the cafe when there is a very ftrong, bride circulation. It aifo happens if the vein be fituated in contact with, in artery. C 26 ) teries in fevers, obferves, that their being " elaftic, and conftantly endeavouring to contract themfelves, they muft, on withdrawing the diftending force, or, in other words, upon a diminution of the quantity of fluids, be in proportion contracted and diminifhed in their fize : and it may be further obferved, that as each part of the vafcular fyftem communicates with every other part of it % fo every degree of diminution of the quantity of fluid in any one part, muft in proportion diminifh the bulk of the vafcular fyftem, and confequently of the whole body."* And why fhall we complicate the works of Nature, by adding mufcular influence, in this inftance, to the elafticity of the vefTels ? Let us revert to the probable intention of Nature in this inftance. Can it be rationally fuppofed that a multiplicity of co-operating caufes would have been brought in to produce an effect, which could have been equally produced by one alone ? Would the watch-maker render the machinery of a watch fo complicated, could his defigned intention be anfwer- ed by greater Simplicity ? Inftances are not wanting, in which there could not poflibly have been any other caufe to influence the circulation than the heart alone -, for the arterial fyftem has been found almoft completely oflified, fo that the arteries were no more than * See his Firft Lines, vol. iv. fefl. 1504.. ( » ) than bony tubes. Morgagni has noticed this in his celebrated work.* He relates cafes which he him- felf faw, and mentions feveral authors who had ob- ferved the fame circumftance.f The arteries, in thofe cafes, could have ferved no other purpofe than that of conducting the blood through the different parts of the body. How then could the patient poffibly have lived a day, if the prefence of mufcu- lar fibres in the arterial fyftem, and their action for carrying on the circulation, had been abfolutely ef- fcntial? There are arteries running through the fubflance of bones, having their external coats clofe- ly adhering to them in their courfe, and confequent- ly incapable of contractility. In what manner then does the blood circulate through the bones, where there can be no contraction or dilatation? And furely the circulation, in fome of the fmaller bones, is as remote from the heart, as any of the capillary verTels whatever. Some, at a lofs to account for the circulation of the blood in the extreme arteries and veins, have had recourfe to the aid of capillary attraction \ J others, to * See his obfervatlons on the arteries in his twentieth letter. •f There is now in the Anatomical Mufeum of Columbia College, the remains of a preparation, in which the arteries throughout the fyftem were oflified. The perfon had lived many years, and died in an advanced age. % See Martin's Philofophy, fubjeft, capillary attraction. ( 23 ) to the affirtance of the electric aura.* That the cir- culation cannot be affifted by capillary attraction, is evident •, if it was, there never would be a difconti* nuance of the circulation while the organization of the body remained entire. The capillary influence would always have the fame effect; that of keeping up the motion of the blood, which is contradicted by fact. Neither can we rationally fuppofe the electric aura to be productive of much benefit in the circulation, as the body is but rarely in fuch a fituation as to be pofitively electrified ; and unlefs it is pofitively elec- trified, the electric aura can have no effect in accele- rating the paffage of the blood through the veffels. From this review of the fubject, which I truft is founded on jufl obfervation and impartial reafon- ing, we may be induced to deny the exirtence of mufcular fibres in the vefTels of the fanguiferous fyftem as effential to the circulation. The argu- ments here offered are founded on fimplicity, the principal characterise of Nature -, and when reafon and experience confirm the truth, it is improper to be governed by mere affertion or hypothecs, how- ever plaufible, or under whatever fanction they may appear. Let us ftudy Nature to afcertain the man- ner in which her works are carried on -, and while we implicitly * See Rirkland's Medico-Chlrurglcal Treatlfe, page 295, ( 2 9 ) implicitly follow this method ; while we deduce our obfervations from fact alone, or reafoning, founded upon incontrovertible analogy, v/e may be more like- ly to difcover the truth. Let no one condemn me, in thus having endeavoured impartially to invefti- gate a fubjedt which may be of much more im- portance than we at prefent are aware of. Let thofe who may perufe thefe few obfervations, can- didly examine the principles upon which they are founded, before they juftify or condemn them; and while calm deliberation takes the lead of hafty con- clufion, they will have caufe rather to confirm, than invalidate the opinion, that the arteries and veins, excepting the power refulting from their elafticity, are nothing more than paffive conductors to the blood through the various parts of the fyffem,* * I have purpofely avoided fpeaking any thing on the manner in which the chyle and lymph get into the blood, for the want of opportunities to inveftigate it. But as it appears to me at prefent, the mouths of the ab- forbents are to their fyftem, what the heart is to the fanguiferous. I have alfo avoided attempts to explain any of the phenomena, explicable by the fuppofition of the increafed action of the veiTels of a particular part. The bounds prefcribed to this Treatife are too fmall to admit them $ and fhouid there be any which at prefent are not explicable without a belief of mufcu- larity in the veffels, though in thefe cafes they are explained by a fuppofi- tion, it ftill does not follow that our principles mufi fali 5 for it cannot be fuppofed that man, who is an imperfect being, can be adequate to the ex-> planation of all the phenomena of Nature. FINIS, £ COLUMBIA UNIVERSITY LIBRARIES This book is due on the date indicated below, or at the expiration of a definite period after the date of borrowing, as provided by the rules of the Library or by special arrange- ment with the Librarian in charge. DATE BORROWED DATE DUE DATE BORROWED DATE DUE // •"' , . , J > ■■ ¥ C28(l14l)M100 I M-QP101 Post An inaug-j disprove th fibres in +. 05 cc m ^^QJ — i Sfji >■ j^s. (0 =*• ■* lu r\j ^ =r~> g Q ""•j*^^^ - ^ - ? 1 ■ = O ?e~ ft-QP/oi ±Q cular pf7~ L,' ', c nr