the circulation of the blood-第2章

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What　Erasistratus　made　out　was　that；　at　the　roots　of　the　aorta　and　the
pulmonary　artery　（Fig。　　1）　there　were　valves；　which　opened　in　the
direction　indicated　by　the　arrows；　and；　on　the　other　hand；　that　at　the
junction　of　what　he　called　the　veins　with　the　heart　there　were　other
valves；　which　also　opened　again　in　the　direction　indicated　by　the
arrows。　　This　was　a　very　capital　discovery；　because　it　proved　that　if
the　heart　was　full　of　fluid；　and　if　there　were　any　means　of　causing
that　fluid　in　the　ventricles　to　move；　then　the　fluid　could　move　only　in
one　direction；　for　you　will　observe　that；　as　soon　as　the　fluid　is
compressed；　the　two　valves　between　the　ventricles　and　the　veins　will　be
shut；　and　the　fluid　will　be　obliged　to　move　into　the　arteries；　and；　if
it　tries　to　get　back　from　them　into　the　heart；　it　is　prevented　from
doing　so　by　the　valves　at　the　origin　of　the　arteries；　which　we　now　call
the　semilunar　valves　（half…moon　shaped　valves）；　so　that　it　is
impossible；　if　the　fluid　move　at　all；　that　it　should　move　in　any　other
way　than　from　the　great　veins　into　the　arteries。　　Now　that　was　a　very
remarkable　and　striking　discovery。

But　it　is　not　given　to　any　man　to　be　altogether　right　（that　is　a
reflection　which　it　is　very　desirable　for　every　man　who　has　had　the
good　luck　to　be　nearly　right　once；　always　to　bear　in　mind）；　and
Erasistratus；　while　he　made　this　capital　and　important　discovery；　made　a
very　capital　and　important　error　in　another　direction；　although　it　was
a　very　natural　error。　　If；　in　any　animal　which　is　recently　killed；　you
open　one　of　those　pulsating　trunks　which　I　referred　to　a　short　time
ago；　you　will　find；　as　a　general　rule；　that　it　either　contains　no　blood
at　all　or　next　to　none；　but　that；　on　the　contrary；　it　is　full　of　air。
Very　naturally；　therefore；　Erasistratus　came　to　the　conclusion　that
this　was　the　normal　and　natural　state　of　the　arteries；　and　that　they
contained　air。　　We　are　apt　to　think　this　a　very　gross　blunder；　but；　to
anybody　who　is　acquainted　with　the　facts　of　the　case；　it　is；　at　first
sight；　an　exceedingly　natural　conclusion。　Not　only　so；　but　Erasistratus
might　have　very　justly　imagined　that　he　had　seen　his　way　to　the　meaning
of　the　connection　of　the　left　side　of　the　heart　with　the　lungs；　for　we
find　that　what　we　now　call　the　pulmonary　vein　is　connected　with　the
lungs；　and　branches　out　in　them　（Fig。　1）。　Finding　that　the　greater　part
of　this　system　of　vessels　was　filled　with　air　after　death；　this　ancient
thinker　very　shrewdly　concluded　that　its　real　business　was　to　receive
air　from　the　lungs；　and　to　distribute　that　air　all　through　the　body；　so
as　to　get　rid　of　the　grosser　humours　and　purify　the　blood。　　That　was　a
very　natural　and　very　obvious　suggestion；　and　a　highly　ingenious　one；
though　it　happened　to　be　a　great　error。　　You　will　observe　that　the　only
way　of　correcting　it　was　to　experiment　upon　living　animals；　for　there
is　no　other　way　in　which　this　point　could　be　settled。

Fig。2；The　Course　of　the　Blood　according　to　Galen　（A。D。　170）。

And　hence　we　are　indebted；　for　the　correction　of　the　error　of
Erasistratus；　to　one　of　the　greatest　experimenters　of　ancient　or　modern
times；　Claudius　Galenus；　who　lived　in　the　second　century　after　Christ。
I　say　it　was　to　this　man　more　than　any　one　else；　because　he　knew　that
the　only　way　of　solving　physiological　problems　was　to　examine　into　the
facts　in　the　living　animal。　And　because　Galen　was　a　skilful　anatomist；
and　a　skilful　experimenter；　he　was　able　to　show　in　what　particulars
Erasistratus　had　erred；　and　to　build　up　a　system　of　thought　upon　this
subject　which　was　not　improved　upon　for　fully　1；300　years。　　I　have
endeavoured；　in　Fig。　2；　to　make　clear　to　you　exactly　what　it　was　he
tried　to　establish。　　You　will　observe　that　this　diagram　is　practically
the　same　as　that　given　in　Fig。　1；　only　simplified。　　The　same　facts　may
be　looked　upon　by　different　people　from　different　points　of　view。　Galen
looked　upon　these　facts　from　a　very　different　point　of　view　from　that
which　we　ourselves　occupy；　but；　so　far　as　the　facts　are　concerned；　they
were　the　same　for　him　as　for　us。　　Well　then；　the　first　thing　that　Galen
did　was　to　make　out　experimentally　that；　during　life；　the　arteries　are
not　full　of　air；　but　that　they　are　full　of　blood。　　And　he　describes　a
great　variety　of　experiments　which　he　made　upon　living　animals　with　the
view　of　proving　this　point；　which　he　did　prove　effectually　and　for　all
time；　and　that　you　will　observe　was　the　only　way　of　settling　the
matter。　　Furthermore；　he　demonstrated　that　the　cavities　of　the　left
side　of　the　heartwhat　we　now　call　the　left　auricle　and　the　left
ventricleare；　like　the　arteries；　full　of　blood　during　life；　and　that
that　blood　was　of　the　scarlet　kindarterialised；　or　as　he　called　it
〃pneumatised；〃　blood。　　It　was　known　before；　that　the　pulmonary　artery；
the　right　ventricle；　and　the　veins；　contain　the　darker　kind　of　blood；
which　was　thence　called　venous。　　Having　proved　that　the　whole　of　the
left　side　of　the　heart；　during　life；　is　full　of　scarlet　arterial　blood；
Galen's　next　point　was　to　inquire　into　the　mode　of　communication
between　the　arteries　and　veins。　　It　was　known　before　his　time　that　both
arteries　and　veins　branched　out。　　Galen　maintained；　though　he　could　not
prove　the　fact；　that　the　ultimate　branches　of　the　arteries　and　veins
communicated　together　somehow　or　other；　by　what　he　called
'anastomoses'；　and　that　these　'anastomoses'　existed　not　only　in　the　body
in　general　but　also　in　the　lungs。　　In　the　next　place；　Galen　maintained
that　all　the　veins　of　the　body　arise　from　the　liver；　that　they　draw　the
blood　thence　and　distribute　it　over　the　body。　　People　laugh　at　that
notion　now…a…days；　but　if　anybody　will　look　at　the　facts　he　will　see
that　it　is　a　very　probable　supposition。　　There　is　a　great　vein　（hepatic
veinFig。　1）　which　rises　out　of　the　liver；　and　that　vein　goes　straight
into　the　'vena　cava'　（Fig。　1）　which　passes　to　the　heart；　being　there
joined　by　the　other　veins　of　the　body。　　The　liver　itself　is　fed　by　a
very　large　vein　（portal　veinFig。　1）；　which　comes　from　the　alimentary
canal。　　The　way　the　ancients　looked　at　this　matter　was；　that　the　food；
after　being　received　into　the　alimentary　canal；　was　then　taken　up　by　the
branches　of　this　great　vein；　which　are　called　the　'vena　portae'；　just
as　the　roots　of　a　plant　suck　up　nourishment　from　the　soil　in　which　it
lives；　that　then　it　was　carried　to　the　liver；　there　to　be　what　was
called　〃concocted；〃　which　was　their　phrase　for　its　conversion　into
substances　more　fitted　for　nutrition　than　previously　existed　in　it。
They　then　supposed　that　the　next　thing　to　be　done　was　to　distribute
this　fluid　through　the　body；　and　Galen　like　his　predecessors；　imagined
that　the　〃concocted〃　blood；　having　entered　the　great　'vena　cava'；　was
distributed　by　its　ramifications　all　over　the　body。　　So　that；　in　his
view　（Fig。　2）；　the　course　of　the　blood　was　from　the　intestine　to　the
liver；　and　from　the　liver　into　the　great　'vena　cava'；　including　what　we
now　call　the　right　auricle　of　the　heart；　whence　it　was　distributed　by
the　branches　of　the　veins。　　But　the　whole　of　the　blood　was　not　thus
disposed　of。　　Part　of　the　blood；　it　was　supposed；　went　through　what　we
now　call　the　pulmonary　arteries　（Fig。　1）；　and；　branching　out　there；　gave
exit　to　certain　〃fuliginous〃　products；　and　at　the　same　time　took　in
from　the　air　a　something　which　Galen　calls　the　'pneuma'。　　He　does　not
know　anything　about　what　we　call　oxygen；　but　it　is　astonishing　how　very
easy　it　would　be　to　turn　his　language　into　the　equivalent　of　modern
chemical　theory。　　The　old　philosopher　had　so　just　a　suspicion　of　the
real　state　of　affairs　that　you　could　make　use　of　his　language　in　many
cases；　if　you　substituted　the　word　〃oxygen；〃　which　we　now…a…days　use；
for　the　word　'pneuma'。　　Then　he　imagined　that　the　blood；　further
concocted　or　altered　by　contact　with　the　'pneuma'；　passed　to　a　certain
extent　to　the　left　side　of　the　heart。　　So　that　Galen　believed　that
there　was　such　a　thing　as　what　is　now　called　the　pulmonary
circulation。　　He　believed；　as　much　as　we　do；　that　the　blood　passed
through　the　right　side　of　the　heart；　through　the　artery　which　goes　to
the　lungs；　through　the　lungs　themselves；　and　back　by　what　we　call　the
pulmonary　veins　to　the　left　side　of　the　heart。　　But　he　thought　it　was
only　a　very　small　portion　of　the　blood　which　passes　to　the　right　side　of
the　heart　in　this　way；　the　rest　of　the　blood；　he　thought；　passed
through　the　partition　which　separates　the　two　ventricles　of　the　heart。
He　describes　a　number　of　small　pits；　which　really　exist　there；　as
holes；　and　he　supposed　that　the　greater　part　of　the　blood　passed
through　these　holes　from　the　right　to　the　left　ventricle　（Fig　2）。

It　is　of　great　importance　you　should　clearly　understand　these　teachings
of　Galen；　because；　as　I　said　just　now；　they　sum　up　all　that　anybody
knew　until　the　revival　of　learning；　and　they　come　to　thisthat　the
blood　having　passed　from　the　stomach　and　intestines　through　the　liver；
and　having　entered　the　great　veins；　was　by　them　distributed　to　every
part　of　the　body；　that　part　of　the　blood；　thus　distributed；　entered　the
arterial　system　by　the　'anastomoses'；　as　Galen　called　them；　in　the
lungs；　that　a　very　small　portion　of　it　entered　the　arteries　by　the
'anastomoses'　in　the　body　generally；　but　that　the　greater　part　of　it
passed　through　the　septum　of　the　heart；　and　so　entered　the　left　side
and　mingled　with　the　pneumatised　blood；　which　had　been　subjected　to　the
air　in　the　lungs；　and　was　then　distributed　by　the　arteries；　and
eventually　mixed　with　the　currents　of　blood；　coming　the　other　way；
through　the　veins。

Yet　one　other　point　about　the　views　of　Galen。　　He　thought　that　both　the
contractions　and　dilatations　of　the　heartwhat　we　call　the　'systole'
or　contraction　of　the　heart；　and　the　'diastole'　or　dilatationGalen
thought　that　these　were　both　active　movements；　that　the　heart　actively
dilated；　so　that　it　had　a　sort　of　sucking　power　upon　the　fluids　which
had　access　to　it。　　And　again；　with　respect　to　the　movements　of　the
pulse；　which　anybody　can　feel　at　the　wrist　and　elsewhere；　Galen　was　of
opinion　that　the　walls　of　the　arteries　partook　of　that　which　he
supposed　to　be　the　nature　of　the　walls　of　the　heart；　and　that　they　had
the　power　of　alternately　actively　contracting　and　actively　dilating；　so
that　he　is　careful　to　say　that　the　nature　of　the　pulse　is　comparable；
not　to　the　movement　of　a　bag；　which　we　fill　by　blowing　into　it；　and
which　we　empty　by　drawing　the　air　out　of　it；　but　to　the　action　of　a
bellows；　which　is　actively　dilated　and　actively　compressed。

Fig　3。The　course　of　the　blood　from　the　right　to　the　left　side　of　the
heart　（Realdus　Columbus；　1559）。

After　Galen's　time　came　the　collapse　of　the　Roman　Empire；　the　extinction
of　physical　knowledge；　and　the　repression　of　every　kind　of　scientific
inquiry；　by　its　powerful　and　consistent　enemy；　the　Church；　and　that
state　of　things　lasted　until　the　latter　part　of　the　Middle　Ages　saw　the
revival　of　learning。　　That　revival　of　learning；　so　far　as　anatomy　and
physiology　are　concerned；　is　due　to　the　renewed　influence　of　the
philosophers　of　ancient　Greece；　and　indeed；　of　Galen。　　Arabic
commentators　had　translated　Galen；　and　portions　of　h