the circulation of the blood-第4节

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thought　much　about　the　matter；　that　it　was　this　discovery　of　the　valves
of　the　veins　which　led　Harvey　to　imagine　the　course　of　the　circulation
of　the　blood。　　Now　it　did　not　lead　Harvey　to　imagine　anything　of　the
kind。　　He　had　heard　all　about　it　from　his　master；　Fabricius；　who　made　a
great　point　of　these　valves　in　the　veins；　and　he　had　heard　the　theories
which　Fabricius　entertained　upon　the　subject；　whose　impression　as　to
the　use　of　the　valves　was　simply　thisthat　they　tended　to　take　off　any
excess　of　pressure　of　the　blood　in　passing　from　the　heart　to　the
extremities；　for　Fabricius　believed；　with　the　rest　of　the　world；　that
the　blood　in　the　veins　flowed　from　the　heart　towards　the　extremities。
This；　under　the　circumstances；　was　as　good　a　theory　as　any　other；
because　the　action　of　the　valves　depends　altogether　upon　the　form　and
nature　of　the　walls　of　the　structures　in　which　they　are　attached；　and
without　accurate　experiment；　it　was　impossible　to　say　whether　the
theory　of　Fabricius　was　right　or　wrong。　　But　we　not　only　have　the
evidence　of　the　facts　themselves　that　these　could　tell　Harvey　nothing
about　the　circulation；　but　we　have　his　own　distinct　declaration　as　to
the　considerations　which　led　him　to　the　true　theory　of　the　circulation
of　the　blood；　and　amongst　these　the　valves　of　the　veins　are　not
mentioned。

Fig。　4。The　circulation　of　the　blood　as　demonstrated　by　Harvey　（A。D。
1628）。

Now　then　we　may　come　to　Harvey　himself。　　When　you　read　Harvey's
treatise；　which　is　one　of　the　most　remarkable　scientific　monographs
with　which　I　am　acquaintedit　occupies　between　50　and　60　pages　of　a
small　quarto　in　Latin；　and　is　as　terse　and　concise　as　it　possibly　can
bewhen　you　come　to　look　at　Harvey's　work；　you　will　find　that　he　had
long　struggled　with　the　difficulties　of　the　accepted　doctrine　of　the
circulation。　　He　had　received　from　Fabricius；　and　from　all　the　great
authorities　of　the　day；　the　current　view　of　the　circulation　of　the
blood。　　But　he　was　a　man　with　that　rarest　of　all
qualitiesintellectual　honesty；　and　by　dint　of　cultivating　that　great
faculty；　which　is　more　moral　than　intellectual；　it　had　become　impossible
for　him　to　say　he　believed　anything　which　he　did　not　clearly　believe。
This　is　a　most　uncomfortable　peculiarityfor　it　gets　you　into　all
sorts　of　difficulties　with　all　sorts　of　peoplebut；　for　scientific
purposes；　it　is　absolutely　invaluable。　　Harvey　possessed　this
peculiarity　in　the　highest　degree；　and　so　it　was　impossible　for　him　to
accept　what　all　the　authorities　told　him；　and　he　looked　into　the　matter
for　himself。　　But　he　was　not　hasty。　　He　worked　at　his　new　views；　and　he
lectured　about　them　at　the　College　of　Physicians　for　nine　years；　he　did
not　print　them　until　he　was　a　man　of　fifty　years　of　age；　and　when　he
did　print　them　he　accompanied　them　with　a　demonstration　which　has　never
been　shaken；　and　which　will　stand　till　the　end　of　time。　　What　Harvey
proved；　in　short；　was　this　（see　Fig。　4）that　everybody　had　made　a
mistake；　for　want　of　sufficiently　accurate　experimentation　as　to　the
actual　existence　of　the　fact　which　everybody　assumed。　　To　anybody　who
looks　at　the　blood…vessels　with　an　unprejudiced　eye　it　seems　so　natural
that　the　blood　should　all　come　out　of　the　liver；　and　be　distributed　by
the　veins　to　the　different　parts　of　the　body；　that　nothing　can　seem
simpler　or　more　plain；　and　consequently　no　one　could　make　up　his　mind
to　dispute　this　apparently　obvious　assumption。　　But　Harvey　did　dispute
it；　and　when　he　came　to　investigate　the　matter　he　discovered　that　it　was
a　profound　mistake；　and　that；　all　this　time；　the　blood　had　been　moving
in　just　the　opposite　direction；　namely；　from　the　small　ramifications　of
the　veins　towards　the　right　side　of　the　heart。　　Harvey　further　found
that；　in　the　arteries；　the　blood；　as　had　previously　been　known；　was
travelling　from　the　greater　trunks　towards　the　ramifications。　Moreover；
referring　to　the　ideas　of　Columbus　and　of　Galen　（for　he　was　a　great
student　of　literature；　and　did　justice　to　all　his　predecessors）；　Harvey
accepts　and　strengthens　their　view　of　the　course　of　the　blood　through
the　lungs；　and　he　shows　how　it　fitted　into　his　general　scheme。　　If　you
will　follow　the　course　of　the　arrows　in　Fig。　4　you　will　see　at　once
thatin　accordance　with　the　views　of　Columbusthe　blood　passes　from
the　right　side　of　the　heart；　through　the　lungs；　to　the　left　side。　　Then；
adds　Harvey；　with　abundant　proof；　it　passes　through　the　arteries　to　all
parts　of　the　body；　and　then；　at　the　extremities　of　their　branches　in
the　different　parts　of　the　body；　it　passes　（in　what　way　he　could　not
tell；　for　his　means　of　investigation　did　not　allow　him　to　say）　into　the
roots　of　the　ventsthen　from　the　roots　of　the　veins　it　goes　into　the
trunk　and　veinsthen　to　the　right　side　of　the　heartand　then　to　the
lungs；　and　so　on。

That；　you　will　observe；　makes　a　complete　circuit；　and　it　was　precisely
here　that　the　originality　of　Harvey　lay。　　There　never　yet　has　been
produced；　and　I　do　not　believe　there　can　be　produced；　a　tittle　of
evidence　to　show　that；　before　his　time；　any　one　had　the　slightest
suspicion　that　a　single　drop　of　blood；　starting　in　the　left　ventricle
of　the　heart；　passes　through　the　whole　arterial　system；　comes　back
through　the　venous　system；　goes　through　the　lungs；　and　comes　back　to
the　place　whence　it　started。　　But　that　is　the　circulation　of　the　blood；
and　it　was　exactly　this　which　Harvey　was　the　first　man　to　suspect；　to
discover；　and　to　demonstrate。

But　this　was　by　no　means　the　only　thing　Harvey　did。　　He　was　the　first
who　discovered　and　who　demonstrated　the　true　mechanism　of　the　heart's
action。　　No　one；　before　his　time；　conceived　that　the　movement　of　the
blood　was　entirely　due　to　the　mechanical　action　of　the　heart　as　a
pump。　　There　were　all　sorts　of　speculations　about　the　matter；　but　nobody
had　formed　this　conception；　and　nobody　understood　that　the　so…called
systole　of　the　heart　is　a　state　of　active　contraction；　and　the
so…called　diastole　is　a　mere　passive　dilatation。　　Even　within　our　own
age　that　matter　had　been　discussed。　　Harvey　is　as　clear　as　possible
about　it。　　He　says　the　movement　of　the　blood　is　entirely　due　to　the
contractions　of　the　walls　of　the　heartthat　it　is　the　propelling
apparatusand　all　recent　investigation　tends　to　show　that　he　was
perfectly　right。　And　from　this　followed　the　true　theory　of　the　pulse。
Galen　said；　as　I　pointed　out　just　now；　that　the　arteries　dilate　as
bellows；　which　have　an　active　power　of　dilatation　and　contraction；　and
not　as　bags　which　are　blown　out　and　collapse。　　Harvey　said　it　was
exactly　the　contrarythe　arteries　dilate　as　bags　simply　because　the
stroke　of　the　heart　propels　the　blood　into　them；　and；　when　they　relax
again；　they　relax　as　bags　which　are　no　longer　stretched；　simply　because
the　force　of　the　blow　of　the　heart　is　spent。　　Harvey　has　been
demonstrated　to　be　absolutely　right　in　this　statement　of　his；　and　yet；
so　slow　is　the　progress　of　truth；　that；　within　my　time；　the　question　of
the　active　dilatation　of　the　arteries　has　been　discussed。

Thus　Harvey's　contributions　to　physiology　may　be　summed　up　as　follows：
In　the　first　place；　he　was　the　first　person　who　ever　imagined；　and
still　more　who　demonstrated；　the　true　course　of　the　circulation　of　the
blood　in　the　body；　in　the　second　place；　he　was　the　first　person　who
ever　understood　the　mechanism　of　the　heart；　and　comprehended　that　its
contraction　was　the　cause　of　the　motion　of　the　blood；　and　thirdly；　he
was　the　first　person　who　took　a　just　view　of　the　nature　of　the　pulse。
These　are　the　three　great　contributions　which　he　made　to　the　science　of
physiology；　and　I　shall　not　err　in　sayingI　speak　in　the　presence　of
distinguished　physiologists；　but　I　am　perfectly　certain　that　they　will
endorse　what　I　saythat　upon　that　foundation　the　whole　of　our
knowledge　of　the　human　body；　with　the　exception　of　the　motor　apparatus
and　the　sense　organs；　has　been　gradually　built　up；　and　that　upon　that
foundation　the　whole　rests。　　And　not　only　does　scientific　physiology
rest　upon　it；　but　everything　like　scientific　medicine　also　rests　upon
it。　　As　you　knowI　hope　it　is　now　a　matter　of　popular　knowledgeit　is
the　foundation　of　all　rational　speculation　about　morbid　processes；　it
is　the　only　key　to　the　rational　interpretation　of　that　commonest　of　all
indications　of　disease；　the　state　of　the　pulse；　so　that；　both
theoretically　and　practically；　this　discovery；　this　demonstration　of
Harvey's；　has　had　an　effect　which　is　absolutely　incalculable；　and　the
consequences　of　which　will　accumulate　from　age　to　age　until　they　result
in　a　complete　body　of　physiological　science。

Fig。5。The　junction　of　the　arteries　and　veins　by　capillary　tubes；
discovered　by　Malpighi　（A。D。　　1664）。

I　regret　that　I　am　unable　to　pursue　this　subject　much　further；　but　there
is　one　point　I　should　mention。　　In　Harvey's　time；　the　microscope　was
hardly　invented。　　It　is　quite　true　that　in　some　of　his　embryological
researches　he　speaks　of　having　made　use　of　a　hand　glass；　but　that　was
the　most　that　he　seems　to　have　known　anything　about；　or　that　was
accessible　to　him　at　that　day。　And　so　it　came　about；　that；　although　he
examined　the　course　of　the　blood　in　many　of　the　lower　animalswatched
the　pul