a history of science-4-第24节

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re　intense；　in　air　it　is　slower；　the　temperature　is　not　so　high；　but　it　continues　longer。

〃It　is　obvious　that　the　amount　of　heat　liberated　must　increase　or　diminish　with　the　amount　of　oxygen　introduced　in　equal　times　by　respiration。　Those　animals　which　respire　frequently；　and　consequently　consume　much　oxygen；　possess　a　higher　temperature　than　others　which；　with　a　body　of　equal　size　to　be　heated；　take　into　the　system　less　oxygen。　The　temperature　of　a　child　（102　degrees）　is　higher　than　that　of　an　adult　（99。5　degrees）。　That　of　birds　（104　to　105。4　degrees）　is　higher　than　that　of　quadrupeds　（98。5　to　100。4　degrees）；　or　than　that　of　fishes　or　amphibia；　whose　proper　temperature　is　from　3。7　to　2。6　degrees　higher　than　that　of　the　medium　in　which　they　live。　　All　animals；　strictly　speaking；　are　warm…blooded；　but　in　those　only　which　possess　lungs　is　the　temperature　of　the　body　independent　of　the　surrounding　medium。

〃The　most　trustworthy　observations　prove　that　in　all　climates；　in　the　temperate　zones　as　well　as　at　the　equator　or　the　poles；　the　temperature　of　the　body　in　man；　and　of　what　are　commonly　called　warm…blooded　animals；　is　invariably　the　same；　yet　how　different　are　the　circumstances　in　which　they　live。

〃The　animal　body　is　a　heated　mass；　which　bears　the　same　relation　to　surrounding　objects　as　any　other　heated　mass。　It　receives　heat　when　the　surrounding　objects　are　hotter；　it　loses　heat　when　they　are　colder　than　itself。　　We　know　that　the　rapidity　of　cooling　increases　with　the　difference　between　the　heated　body　and　that　of　the　surrounding　mediumthat　is；　the　colder　the　surrounding　medium　the　shorter　the　time　required　for　the　cooling　of　the　heated　body。　How　unequal；　then；　must　be　the　loss　of　heat　of　a　man　at　Palermo；　where　the　actual　temperature　is　nearly　equal　to　that　of　the　body；　and　in　the　polar　regions；　where　the　external　temperature　is　from　70　to　90　degrees　lower。

〃Yet　notwithstanding　this　extremely　unequal　loss　of　heat；　experience　has　shown　that　the　blood　of　an　inhabitant　of　the　arctic　circle　has　a　temperature　as　high　as　that　of　the　native　of　the　South；　who　lives　in　so　different　a　medium。　　This　fact；　when　its　true　significance　is　perceived；　proves　that　the　heat　given　off　to　the　surrounding　medium　is　restored　within　the　body　with　great　rapidity。　This　compensation　takes　place　more　rapidly　in　winter　than　in　summer；　at　the　pole　than　at　the　equator。

〃Now　in　different　climates　the　quantity　of　oxygen　introduced　into　the　system　of　respiration；　as　has　been　already　shown；　varies　according　to　the　temperature　of　the　external　air；　the　quantity　of　inspired　oxygen　increases　with　the　loss　of　heat　by　external　cooling；　and　the　quantity　of　carbon　or　hydrogen　necessary　to　combine　with　this　oxygen　must　be　increased　in　like　ratio。　It　is　evident　that　the　supply　of　heat　lost　by　cooling　is　effected　by　the　mutual　action　of　the　elements　of　the　food　and　the　inspired　oxygen；　which　combine　together。　　To　make　use　of　a　familiar；　but　not　on　that　account　a　less　just　illustration；　the　animal　body　acts；　in　this　respect；　as　a　furnace；　which　we　supply　with　fuel。　It　signifies　nothing　what　intermediate　forms　food　may　assume；　what　changes　it　may　undergo　in　the　body；　the　last　change　is　uniformly　the　conversion　of　carbon　into　carbonic　acid　and　of　its　hydrogen　into　water；　the　unassimilated　nitrogen　of　the　food；　along　with　the　unburned　or　unoxidized　carbon；　is　expelled　in　the　excretions。　In　order　to　keep　up　in　a　furnace　a　constant　temperature；　we　must　vary　the　supply　of　fuel　according　to　the　external　temperaturethat　is；　according　to　the　supply　of　oxygen。

〃In　the　animal　body　the　food　is　the　fuel；　with　a　proper　supply　of　oxygen　we　obtain　the　heat　given　out　during　its　oxidation　or　combustion。〃＇3＇


BLOOD　CORPUSCLES；　MUSCLES；　AND　GLANDS

Further　researches　showed　that　the　carriers　of　oxygen；　from　the　time　of　its　absorption　in　the　lungs　till　its　liberation　in　the　ultimate　tissues；　are　the　red　corpuscles；　whose　function　had　been　supposed　to　be　the　mechanical　one　of　mixing　of　the　blood。　　It　transpired　that　the　red　corpuscles　are　composed　chiefly　of　a　substance　which　Kuhne　first　isolated　in　crystalline　form　in　1865；　and　which　was　named　haemoglobina　substance　which　has　a　marvellous　affinity　for　oxygen；　seizing　on　it　eagerly　at　the　lungs　vet　giving　it　up　with　equal　readiness　when　coursing　among　the　remote　cells　of　the　body。　When　freighted　with　oxygen　it　becomes　oxyhaemoglobin　and　is　red　in　color；　when　freed　from　its　oxygen　it　takes　a　purple　hue；　hence　the　widely　different　appearance　of　arterial　and　venous　blood；　which　so　puzzled　the　early　physiologists。

This　proof　of　the　vitally　important　role　played　by　the　red…blood　corpuscles　led；　naturally；　to　renewed　studies　of　these　infinitesimal　bodies。　It　was　found　that　they　may　vary　greatly　in　number　at　different　periods　in　the　life　of　the　same　individual；　proving　that　they　may　be　both　developed　and　destroyed　in　the　adult　organism。　　Indeed；　extended　observations　left　no　reason　to　doubt　that　the　process　of　corpuscle　formation　and　destruction　may　be　a　perfectly　normal　onethat；　in　short；　every　red…blood　corpuscle　runs　its　course　and　dies　like　any　more　elaborate　organism。　They　are　formed　constantly　in　the　red　marrow　of　bones；　and　are　destroyed　in　the　liver；　where　they　contribute　to　the　formation　of　the　coloring　matter　of　the　bile。　　Whether　there　are　other　seats　of　such　manufacture　and　destruction　of　the　corpuscles　is　not　yet　fully　determined。　Nor　are　histologists　agreed　as　to　whether　the　red…blood　corpuscles　themselves　are　to　be　regarded　as　true　cells；　or　merely　as　fragments　of　cells　budded　out　from　a　true　cell　for　a　special　purpose；　but　in　either　case　there　is　not　the　slightest　doubt　that　the　chief　function　of　the　red　corpuscle　is　to　carry　oxygen。

If　the　oxygen　is　taken　to　the　ultimate　cells　before　combining　with　the　combustibles　it　is　to　consume；　it　goes　without　saying　that　these　combustibles　themselves　must　be　carried　there　also。　Nor　could　it　be　in　doubt　that　the　chiefest　of　these　ultimate　tissues；　as　regards；　quantity　of　fuel　required；　are　the　muscles。　A　general　and　comprehensive　view　of　the　organism　includes；　then；　digestive　apparatus　and　lungs　as　the　channels　of　fuel…supply；　blood　and　lymph　channels　as　the　transportation　system；　and　muscle　cells；　united　into　muscle　fibres；　as　the　consumption　furnaces；　where　fuel　is　burned　and　energy　transformed　and　rendered　available　for　the　purposes　of　the　organism；　supplemented　by　a　set　of　excretory　organs；　through　which　the　waste　productsthe　ashesare　eliminated　from　the　system。

But　there　remain；　broadly　speaking；　two　other　sets　of　organs　whose　size　demonstrates　their　importance　in　the　economy　of　the　organism；　yet　whose　functions　are　not　accounted　for　in　this　synopsis。　These　are　those　glandlike　organs；　such　as　the　spleen；　which　have　no　ducts　and　produce　no　visible　secretions；　and　the　nervous　mechanism；　whose　central　organs　are　the　brain　and　spinal　cord。　　What　offices　do　these　sets　of　organs　perform　in　the　great　labor…specializing　aggregation　of　cells　which　we　call　a　living　organism？

As　regards　the　ductless　glands；　the　first　clew　to　their　function　was　given　when　the　great　Frenchman　Claude　Bernard　（the　man　of　whom　his　admirers　loved　to　say；　〃He　is　not　a　physiologist　merely；　he　is　physiology　itself〃）　discovered　what　is　spoken　of　as　the　glycogenic　function　of　the　liver。　The　liver　itself；　indeed；　is　not　a　ductless　organ；　but　the　quantity　of　its　biliary　output　seems　utterly　disproportionate　to　its　enormous　size；　particularly　when　it　is　considered　that　in　the　case　of　the　human　species　the　liver　contains　normally　about　one…fifth　of　all　the　blood　in　the　entire　body。　Bernard　discovered　that　the　blood　undergoes　a　change　of　composition　in　passing　through　the　liver。　　The　liver　cells　（the　peculiar　forms　of　which　had　been　described　by　Purkinje；　Henle；　and　Dutrochet　about　1838）　have　the　power　to　convert　certain　of　the　substances　that　come　to　them　into　a　starchlike　compound　called　glycogen；　and　to　store　this　substance　away　till　it　is　needed　by　the　organism。　　This　capacity　of　the　liver　cells　is　quite　independent　of　the　bile…making　power　of　the　same　cells；　hence　the　discovery　of　this　glycogenic　function　showed　that　an　organ　may　have　more　than　one　pronounced　and　important　specific　function。　But　its　chief　importance　was　in　giving　a　clew　to　those　intermediate　processes　between　digestion　and　final　assimilation　that　are　now　known　to　be　of　such　vital　significance　in　the　economy　of　the　organism。

In　the　forty　odd　years　that　have　elapsed　since　this　pioneer　observation　of　Bernard；　numerous　facts　have　come　to　light　showing　the　extreme　importance　of　such　intermediate　alterations　of　food…supplies　in　the　blood　as　that　performed　by　the　liver。　It　has　been　shown　that　the　pancreas；　the　spleen；　the　thyroid　gland；　the　suprarenal　capsules　are　absolutely　essential；　each　in　its　own　way；　to　the　health　of　the　organism；　through　metabolic　changes　which　they　alone　seem　capable　of　performing；　and　it　is　suspected　that　various　other　tissues；　including　even　the　muscles　themselves；　have　somewhat　similar　metabolic　capacities　in　addition　to　their　recognized　functions。　But　so　extremely　intricate　is　the　chemistry　of　the　substances　involved　that　in　no　single　case　has　the　exact　nature　of　the　metabolisms　wrought　by　these　organs　been　fully