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                 A K

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. Prefidenty

            FOR THE DEGREE OF

   DOCTOR  OF  PHTSIC;
      ON THE THIRTIETH DAY OF APRIL, 1793.


    By  JOTHAM POST, A. B.
          Citiien of the State of New-York.
     CRIMINOSA, EST CELERITAS, IN JUDICANDO.



            N E W--Y 6 R K:
Printed by T. and J. Swords, Printers to the Faculty of Phvfic of
              Columbia College,
               — 1793.—. 
Imprimatur,
Samuel L. MitchilL 
T 0
RICHARD   BAYLEY,
           Profeflbr of Anatomy,
                   AND

   WRIGHT    POST,
           Profeflbr of Surgery,

    IN  COLUMBIA COLLEGE:
Grateful Teftimony for their Care and Attention to him, in his
                  Medical Studies,
DISSERTATION
         IS ADDRESSED,
               By their Pupil,

                       The  AUTHOR. 
 
A N
INAUGURAL DISSERTATION,  &c.
 OIN C E the difcovery  of the circulation of the
 blood, the attention of Phyfiologifts has been excited
 tq 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 action might
 be aflifted, and  the routine of the circulation facili-
 tated.   They have fuppofed the veffels 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 fubject is of more import-
 ance than might at firft be imagined; for upon a fup-
 pofition of the exiftence 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 
                     (   6  )
many important difeafes.* It is true, fuch an opinion,
at firft view, exhibits fome degree of plaufibility; but
upon mere accurate investigation, it appears to be
rather the creature of imagination, than the refult of
impartial obfervation and deliberate reafoning.

   Many eminent characters have made experiments
to afcertain the projectile force  of the  heart-f, fome
of 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 ftrengthj is confiderable, and
to  thofe who are willing to be unbiaffed  by pre-
poftefted opinions, fufficient to propel the  blood
through every minute ramification of the arteries,
and veins, independent of their mufcular power, ad-
mitting fuch.   Why then ihould we fly to the aid of
a caufe, the afiiftance of which is not at all requifite ?

   The opinion,  that mufcular fibres  encircling the
 veftels  are  neceftary for the circulation, moft pro-
 bably muft have  originated from conjecture.   But
                                         conjecture,
   * Among thefe, fevers and irvflammations hold no ineonfiderable rank.
  See Cullen's Firft Lines, volume firft, fubgeft pyrexiae.  See  Bell and
  Cullen on the proximate caufe of inflammation.
   + See Hales's Hsemaftaticks.  See Keil's Anatomy, and Calculations
  on the Force of the Heart, &c.
   X By  the words strength and power, which  are ufed throughout
  this Treatife, 1 would not wilh to be understood to mean any great exer-
  tion. The terms are ufed for war.t of more expreflive ones. 
                     (  7  )    .
conjecture, though fometimes of ufe to the ingeni-
ous in the difcovery of truth, unlefe well fupported
by fact, fhould never be miftaken for demonftration.

   The learned Haller,* who has applied much care,
and  attention to the inveftigation of  phyfiological
fubjects, fuppofed the exiftence of mufcular fibres in
the vefTels as requifite to aflift 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 Angu-
lar inftance of prejudice, to afTert the eflentiality, and
believe the exiftence of mufcular fibres  in the vefTels,
as requifite for carrying on the circulation, though
unfupported, and in a manner contradicted  by his
own experiments.  But what  may we not expect
from refearches made to fupport a favourite hypo-
 thefis!

   If, from the prefence of  mufcular  fibres  on the
aorta-j- 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,
                                              thev
                                                 j
          * Vide experlmenta  de irritabilitate, feet. 2d.
   •J- Becaufe in fome inftances they  have been ken on  the aorta, the ex-
 iftence of mufcular fibres by analogy Has been inferred throughout veiiels
 of the circulating fyftem. 
                    (   8   )
 they  are  moft probably the confequence of fome
 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 th& middle coat of the
 aorta, as  is generally imagined and afierted,  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 fact, 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
 Phyfiologift will deny, that mufcular fibres, or at
 leaft 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 ftate, been able
 fo difcover the leaft veftige of mufcular fibres in them.
                                          Upon 
                    (   9   )
   Upon the fuppofition of the exiftence of mufcular
 fibres in the vefTels, as efiential to the circulation,
 and an increafe 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 juftify the
 opinion.  However, fuppofing 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 eafily feen; for, according to the ad-
 vocates for mufcular power in the vefTels, thefe are
 lefs 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 relinquilh the idea, from
 its being fo very generally believed, that there was a
fyjiole and diaftole 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  iffued
 from their mouths, any  farther than that it came
                                            forth 
                    C   10   )
forth with an increafed or diminifhed velocity, as the
heart contracted or dilated.   The diameter of  the
ftream apparently remained the fame while the veflels
were in a ftate of diftention;  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 fides have not the leaft motion of
this kind, whether the  blood flows freely through
them, or whether it is interrupted at the extremity
of the divided veffel; which experiment we made to
prevent our being miftaken,  by any alteration that
might take place from the refiftance to the blood be-
ing entirely  removed;  but the  fides  of the veflels
were 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  aflift 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, fhew 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 ox imme-
diately after his throat was cut, I threw into it fome
                                           water,

 * See-Khkland's Medico-Chirurgical Treatife, volume the firft, pa»e 309. 
                   (   II   )
water, about  the  temperature of the blood,  but
could not obferve the leaft contraction  in it, unlefs
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 considered abfolutely conclu-
five of the exiftence of mufcular fibres in the fangui-
ferous fyftem as effential  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 ftretch,  muft
necefTarily contract,  and  force out the fluid  from
within, as if by a mufcular contraction;  and the ve-
locity of the fluid rufhing out would be nearly pro-
portionate to the diftention made.
   In order farther to illuftrate 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 effential 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 muft have done if mufcular
                                          agency 
                    (   i2   )
 agency had been the caufe, regularly trickled dowri
 the fides of the veffel.   The artery, however,  was
 not  much diftended; otherwife, from the re-action
 of the elaftic power, I fuppofe  the  blood would at
 firft have ifliied out in a  ftream.

   At the Anatomical Theatre of Columbia College
 I have  ken Profeffor Bayley lay bare the carotid ar-
 tery of a dog, nearly three inches in length, in order
 to afcertain whether it v/ould 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 fifhes and
frogs,  and during the whole time the fides 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 Ha!ler.-f-

   So far experiments feem directly conclufive, that
the arteries and veins, excepting their elafticity, are
pafiive conductors to their contained fluids. Obfer-
                                           vation
 * The pulfe, however, was plainly felt at every contraction of the heart.
 f See Kirkland's Medico-Chirurgical Enquiry, volume firft, page 310. 
                    (   13   )
ration arid reafon may afford us many more argu-
ments to confirm the opinion.

   From the ftructure  of the heart, we  may draw
very forcible  reafons, to  induce us  to believe, that
the arteries and veins  afford no other afliftance in
the circulation, than that which arifes from their elas-
ticity.  The right ventricle, compared with the left,
has but very little ftrength.  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 moft diftant parts of the
body,  as well as thofe which are lefs remote, has
its power  proportionably greater.   Does  not  this
great difproportion 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 fepa-
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
neceffity of a heart endowed with fo much mufcular
force ?  or, indeed, why  the neceffity 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
tiad 
                    C  14   )
   Had the arteries been originally designed 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 adtion.    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 unneceflary.  But this would evidently ap-
pear to have been the cafe, fhould we allow the ex-
iftence of mufcular fibres in the vefTels; for between
the coat which is find to  be mufcular, and the blood
which is to excite it into action,  is interpofed a firm
denfe membrane.*   Membranes, in  a  found ftate,
are infenfible:-f- 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 affift-
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
affiftance  was  requifite,  why were not the vefTels
made into hollow mufcles ?

                                           Nature
   * See Haller's Firft Lines, fedYion 51. See Filconar's Synopfis, page 16.
   f Noted from ProfefTor Bayley's le&ureon membranes, and membra-
 nous parts. 
                    (  *5  )
   Nature is invariably the fame in her different fpe-
cies of creation; and hence, if mufcular fibres  have
been (etn in the vefTels of one animal in a natural
ftate,  it is prefumable that they would be demon-
jftrable in another of the fame fpecies, which is con-
tradictory to experience,
   On perufing fome notes taken from Doctor Wil-
liam Hunter's lectures in 1771,  I find that he does
not admit of any other affiftance from the veffels of
the fanguiferous fyftem,  excepting their elafticity,
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 exiftence of mufcular fibres in the vefTels to
affift the circulation, fhould have great weight;  for
he never would have inculcated fuch 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 Obfervatioju on the Vital and Involuntary Motions, fubjecl,
 fyftole and diaftolc of the  arteries. 
                     (   16   )
 the  fyftole and  diaftole of the arteries, attributes
 their contraction principally to  their elafticity.   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 hypothefis.

   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  veffels 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
 ventralis,  where they are mixed together, and from
 thence they enter the tranfverfe finus or trunk of the
 vena portae 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
portae,  and by the lateral pulfations of the ramifica-
tions of the hepatic artery, its courfe muft be  very
 flow."J

                                              The
  * This is often the cafe, that becaufe an opinion is generally prevalent
 we readily fubfcribe to it, whether right or wrong.
  •f- The blood from the fpleen, pancreas, and inteftines.
  % The flownefs of the circulation here, however more probably, arifes
 from  the greater capacity of the veins compired to. the arteries,  which;
 carry bipod to the abdominal vifcera. 
                     C   17   )
   The manner in which the  blood paffes 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 reT
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 confidered as
one continued tube, filled with  a fluid which keeps
them in a ftate of diftention; and therefore,  what-
ever caufe fhould  propel this fluid from the heart in
the courfe of the arteries, will of neceffity caufe fb
much as is propelled to pafs out of the veins.-j-
Now, the ventricles propel;  and as much as they
propel,  fo much the auricles receive.  This procefs
muft  continue,  independent of  mufcular  affiftance
from fibres furrounding  the vefTels to aid the cir-
culation, as long as the  heart is capable of continu-
ing its action.!
                                              Since,
  * Utriufque Aumcur.* contradlio eodem tempore perficetur, relaxato
tunc utroque ventriculo, et hi rurfus eodem tempore fe contrahunt
auriculis fimul  relaxatis.  Vide  Confpeft. Medicin. Theoret.  auftore
Jacobo Gregory, fection 419.
  f Hence we may fee, why in aneurifms there is an interrupted pulfe.
  t We may hence fee why, after blood has  been drawn from the body,
when there has been a great plethora, the pulfe becomes fo much more
full,  free,  and eafy, as the heart  has a better opportunity of perforiniag
)ts office. 
                    C   18   )
   Since, according to the mufcular hypothefis, fome
other power is wanting befides the heart; and fincc
an increafe of that power becomes  more  requifite
in thofe parts which are more diftant from the cen-
ter of the circulation,  the arteries, which are called
capillary,  mould be  furnifhed with mufcular fibres,
which, did they exift, would be eafily demonftrable,
and the veins, from an external view, would reprefent
nothing but mere flefhy cylinders.   This, however*
is contradicted by experience; for the coats of the
capillary, or extreme arteries, are fb thin and delicate
as to become perfectly tranfparent, and the veins, to
appearance, are entirely deftitute of thQ leaft 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  progfeffive 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 inftantaneoufly fhorten
themfelves, and fpontaneoufly return again to their
natural ftate, when the irritating caufe ceafes to act."*
                                           They
  * See Kirkland's Medico-Chirurgical Enquiry, fubjeft, inflammation
in general, page z6o. 
                    C   *9   )
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 timej for at every attempt made by the heart
to fend forward the  blood, the refiftance would be
proportionably increafed,  becaufe the veflels would
become more full, and of courfe jncreafe the action
of their mufcular fibres by its ftimulus;  and fo, in-
ftead of allowing the veflels to dilate, and the blood
to be tranfmitted. with  greater eafe,  they  would \ef-
fen 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 fup-
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 
                      t  20   )
for Bayley laid bare the carotid artery of the above
mentioned  dog,  as well as  in  other inftarices,  but
did not fucceed.

   If mufcular fibres do really  exift  in  the arteries
to aflift  in 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  almoft throughout the  body,
and mufcular motion of courfe  interrupted.   It may
be afked, then, why  the heart  continues its action r
why does it not partake of the general morbid af-
fection ?  The reafbn 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 fyheope.-f-
                                               There
       *  This vis infita of Haller may alfo have an aiding power.
   f I have been favoured with the following cafe, which wilt hereafter
 be pubjifhed 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 fkull.  The fpinal marrow was concufTed ; in confequence of which a
 very general paralyfis followed, attended with a difordered ftate of feveral
 of the functions. But notwithstanding this general affection lafled for fe-
 veral weeks, the circulation of the blood continued unUifturbed.  The 
                     C  2*  )
   There is a wide difference between the Structure
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, muft 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  elafticity.  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
iimilar offices ?

   Some fuppofe the coats of the arteries to be muf-
cular, becaufe of their ftrength and thicknefs.  This,
however, moft 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 action of mufcular fibres, which
receive their influence from the nerves ? The nerves were incapacitated
for action.—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
 in the VefTels are really effential 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 fhould have been thicker, which  is con-
 trary to experience.

   When a degree of inanition  is produced in the
 fyftem, the arteries,  from their elasticity, will con-
 tract considerably, though they  do not embrace the
 blood fo Strongly as before.  The circulation, how-
 ever, continues, which cannot be attributed  to the
 action of mufcular fibres,  even  admitting their ex-
iftence in the  veffels; for  it is difficult to conceive
 how they poffefs the  property of performing their
 office equally in one ftate oS the arteries as in another.
 Yet fuch is the belief of fome who cannot relinquifh
 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 difpofition of
 man too often to grafp at things  beyond the reach of
 comprehension, 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 the fmalleft altera-
                                             tion 
                   (   23   J
tion produced in the action of the heart.   Thus, if
the pulfe be Strong, we judge that the action of the
heart is Strong:  If the action of the heart be weak,
th^ 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, fhould there be a Stoppage made
to the  courSe of the blood in an  artery, the pulfe is
inftantaneoufly deftroyed.  Thus, if preffure be made
on the inguinal  artery Sufficient  to Stop the paflage
of the blood; at the  inftant that it is Stopped, the
pulfe below is immediately deftroyed, and inftantly
returns again when the preffure  is removed.   Now,
if there were mufcular fibres encircling the veffels,
and having a command over them, we cannot ration-
ally SuppoSe that the ftate of the pulfe would fo in-
variably be regulated by the action of  the  heart.
The phaenomena 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 instance,  may reprefent the  heart, and
tubes leading from it, the arteries; in which may be
felt a pulfe,  when the pump is in action,  Similar to
that produced by the action of the heart itfelf,
   From the fact, that the arteries and veins  are
mere  paffive conductors  to  their contained  fluids,
abstracting from  their elasticity, we can eafily ex-
                                           plain. 
                    (   24   )
plain, why, when an animal dies from having its
throat cut, and life itfelf becomes extinct, the blood
ftill continues to flow; for, from the elasticity of the
veffels,  their diameters will  be continually leffening
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 Stimulus  to the veflels, and they  are  of
courfe irritable from the mufcular fibres Surrounding
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  neceSTary  to
carry on the circulation,  they muft of neceffity 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
folium; which is well known to be contradicted 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 perfaltum, but in one  continued Stream, as
we fhould a priori have SuppoSed, from the idea that
the veffels, abstracting from their elasticity, are paf-
five conductors to their contained fluids; but when
                                              the 
                     (   25   y
the parts adjacent to the divided artery become forrie^
what emptied through the given  outlet, the blood
rufhes out per faltum, becaufe they become more full
and turgid at every fyStole of the heart.  If there was
a contraction and dilatation in the veffels, it fhould
become evident in the veins, as they are So far distant
from the influence of the heart; and, of neceffity, the
blood fhould paSs out in thefe perfaltum.  But the ap-
pearance of the blood iffuing from the orifice of a vein
in blood-letting,  entirely contradicts this opinion.*
Indeed, thefe two facts,  that the blood iffues  from
the extreme arteries at firft, and from the veins  moft
generally, in a continued Stream, might be consider-
ed  as abfolutely conclufive  of the non-exifieme of
mufcular  fibres in the fyftem  to aid the circulation;
for did they  exift, the  blood muft always be forced
out with an increafed or diminilhed velocity, accord-
ing to their contraction or dilatation.

  So flrongly does common fenfe  confirm us in the
belief of  elasticity in the arteries, that in common
expreffions we  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,
brifk circulation.  It alfo happens if the vein be fituated in contact with
An artery. 
                   (   26  )
teries in fevers, obferves, that their being " elaftic,
and constantly endeavouring to contract themfelves,
they muft, on withdrawing the distending force, or,
in other words, upon a diminution of the quantity of
fluids, be in proportion contracted and diminifhed in
their Size: and it may be further obferved,  that as
each part of the  vafcular Syftem 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
Shall we complicate the works of Nature, by adding
mufcular influence, in this inftance, to the elasticity
pf the vefTels?

  Let us revert to the probable intention of Nature
in this inftance.   Can it be rationally Suppofed 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 fimplicity ? Instances are not wanting,
in which  there  could  not poffibly have been any
other cauSe to influence the circulation than the heart
alone; for the arterial fyftem has been found almoft
completely offified, So that the arteries were no more
                                            than
          * See his Firft Lines, vol. iv. feet. 1504. 
                     (   27   )
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
thoSe caSes, could have Served 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-
fential?   There are  arteries  running through the
fubftance 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
veffels whatever.

   Some, at a loSs 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 obfervations on the arteries in his twentieth letter.
  •f- There is now in the Anatomical Mufsum of Columbia College, the
remains of a preparation, in which the arteries throughout the fyftem
were oflified.   The perfon  bad lived many years, and died in an advanced
age.
     | See Martin's Philofophy, fubjedt, capillary attraction. 
                    (  *«  )
to the affiftance of the electric aura.*   That the cir-
culation cannot be affifted by capillary attraction, 1*3
evident *, if it was, there never would be a difconti-
nuanee 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 Situation as to be
positively electrified; and unlefs it is positively elec-
trified, the electric aura can have no efrect in accele-
rating the paffage of the blood through the veflels.

   From this review of the fubject, which I truft is
founded  on juft observation and  impartial reaSon-
ing, we may be induced to  deny the exiftence 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 characteristic of Nature;  and when reafon
and experience confirm the  truth,  it is improper to
be governed by mere affertion or hypothefis, how-
ever plaufible, or under whatever Sanction they may
appear.   Let us Study Nature to aScertain the man-
ner in which her works are carried on; and while we
                                       implicidy
* See Kirkland's Medico-Chirurgkal Treatife, page 295. 
                       (   29   )
implicitly follow this method; while we deduce our
obfervations from fact alone, or reafoning, founded
upon incontrovertible analogy, we may be more like-
ly to difcover the truth.   Let no one condemn me,
in thus having  endeavoured impartially  to investi-
gate a  Subject  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 cauSe rather to confirm, than
invalidate the opinion, that the arteries and veins,
excepting the power reSulting from their  elasticity,
are nothing more than paffive conductors to the blood
through the various parts of the fyftem,*
  * 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 meat 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 incrfeafed action of the veflels of a particular part. The
bounds prefcribed to this Treatife are too fmall to admit them j and fhould
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 muft fall; 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.
E 
 
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