medical essays-第34章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！




＇This　Lecture　appears　as　it　would　have　been　delivered　had　the　time　allowed　been　less　strictly；　limited。　　Passages　necessarily　omitted　have　been　restored；　and　points　briefly　touched　have　been　more　fully　considered。　　A　few　notes　have　been　added　for　the　benefit　of　that　limited　class　of　students　who　care　to　track　an　author　through　the　highways　and　by…ways　of　his　reading。　　I　owe　my　thanks　to　several　of　my　professional　brethren　who　have　communicated　with　me　on　subjects　with　which　they　are　familiar；　especially　to　Dr。　John　Dean；　for　the　opportunity　of　profiting　by　his　unpublished　labors；　and　to　Dr。　Hasket　Derby；　for　information　and　references　to　recent　authorities　relating　to　the　anatomy　and　physiology　of　the　eye。＇


The　entrance　upon　a　new　course　of　Lectures　is　always　a　period　of　interest　to　instructors　and　pupils。　　As　the　birth　of　a　child　to　a　parent；　so　is　the　advent　of　a　new　class　to　a　teacher。　　As　the　light　of　the　untried　world　to　the　infant；　so　is　the　dawning　of　the　light　resting　over　the　unexplored　realms　of　science　to　the　student。　　In　the　name　of　the　Faculty　I　welcome　you；　Gentlemen　of　the　Medical　Class；　new…born　babes　of　science；　or　lustier　nurslings；　to　this　morning　of　your　medical　life；　and　to　the　arms　and　the　bosom　of　this　ancient　University。　　Fourteen　years　ago　I　stood　in　this　place　for　the　first　time　to　address　those　who　occupied　these　benches。　　As　I　recall　these　past　seasons　of　our　joint　labors；　I　feel　that　they　have　been　on　the　whole　prosperous；　and　not　undeserving　of　their　prosperity。

For　it　has　been　my　privilege　to　be　associated　with　a　body　of　true　and　faithful　workers；　I　cannot　praise　them　freely　to　their　faces；　or　I　should　be　proud　to　discourse　of　the　harmonious　diligence　and　the　noble　spirit　in　which　they　have　toiled　together；　not　merely　to　teach　their　several　branches；　but　to　elevate　the　whole　standard　of　teaching。

I　may　speak　with　less　restraint　of　those　gentlemen　who　have　aided　me　in　the　most　laborious　part　of　my　daily　duties；　the　Demonstrators；　to　whom　the　successive　classes　have　owed　so　much　of　their　instruction。　They　rise　before　me；　the　dead　and　the　living；　in　the　midst　of　the　most　grateful　recollections。　　The　fair；　manly　face　and　stately　figure　of　my　friend；　Dr。　Samuel　Parkman；　himself　fit　for　the　highest　offices　of　teaching；　yet　willing　to　be　my　faithful　assistant　in　the　time　of　need；　come　back　to　me　with　the　long　sigh　of　regret　for　his　early　loss　to　our　earthly　companionship。　　Every　year　I　speak　the　eulogy　of　Dr。　Ainsworth's　patient　toil　as　I　show　his　elaborate　preparations：　When　I　take　down　my　〃American　Cyclopaedia〃　and　borrow　instruction　from　the　learned　articles　of　Dr。　Kneeland；　I　cease　to　regret　that　his　indefatigable　and　intelligent　industry　was　turned　into　a　broader　channel。　　And　what　can　I　say　too　cordial　of　my　long　associated　companion　and　friend；　Dr。　Hodges；　whose　admirable　skill；　working　through　the　swiftest　and　surest　fingers　that　ever　held　a　scalpel　among　us；　has　delighted　class　after　class；　and　filled　our　Museum　with　monuments　which　will　convey　his　name　to　unborn　generations？

This　day　belongs；　however；　not　to　myself　and　my　recollections；　but　to　all　of　us　who　teach　and　all　of　you　who　listen；　whether　experts　in　our　specialties　or　aliens　to　their　mysteries；　or　timid　neophytes　just　entering　the　portals　of　the　hall　of　science。　　Look　in　with　me；　then；　while　I　attempt　to　throw　some　rays　into　its　interior；　which　shall　illuminate　a　few　of　its　pillars　and　cornices；　and　show　at　the　same　time　how　many　niches　and　alcoves　remain　in　darkness。


SCIENCE　is　the　topography　of　ignorance。　　From　a　few　elevated　points　we　triangulate　vast　spaces；　inclosing　infinite　unknown　details。　　We　cast　the　lead；　and　draw　up　a　little　sand　from　abysses　we　may　never　reach　with　our　dredges。

The　best　part　of　our　knowledge　is　that　which　teaches　us　where　knowledge　leaves　off　and　ignorance　begins。　　Nothing　more　clearly　separates　a　vulgar　from　a　superior　mind；　than　the　confusion　in　the　first　between　the　little　that　it　truly　knows；　on　the　one　hand；　and　what　it　half　knows　and　what　it　thinks　it　knows　on　the　other。

That　which　is　true　of　every　subject　is　especially　true　of　the　branch　of　knowledge　which　deals　with　living　beings。　　Their　existence　is　a　perpetual　death　and　reanimation。　　Their　identity　is　only　an　idea；　for　we　put　off　our　bodies　many　times　during　our　lives；　and　dress　in　new　suits　of　bones　and　muscles。

　　　　　　　　　　　　　　　〃Thou　art　not　thyself；　　　　　　For　thou　exist'st　on　many　a　thousand　grains　　　　　　That　issue　out　of　dust。〃

If　it　is　true　that　we　understand　ourselves　but　imperfectly　in　health；　this　truth　is　more　signally　manifested　in　disease；　where　natural　actions　imperfectly　understood；　disturbed　in　an　obscure　way　by　half…　seen　causes；　are　creeping　and　winding　along　in　the　dark　toward　their　destined　issue；　sometimes　using　our　remedies　as　safe　stepping…stones；　occasionally；　it　may　be；　stumbling　over　them　as　obstacles。

I　propose　in　this　lecture　to　show　you　some　points　of　contact　between　our　ignorance　and　our　knowledge　in　several　of　the　branches　upon　the　study　of　which　you　are　entering。　　I　may　teach　you　a　very　little　directly；　but　I　hope　much　more　from　the　trains　of　thought　I　shall　suggest。　　Do　not　expect　too　much　ground　to　be　covered　in　this　rapid　survey。　　Our　task　is　only　that　of　sending　out　a　few　pickets　under　the　starry　flag　of　science　to　the　edge　of　that　dark　domain　where　the　ensigns　of　the　obstinate　rebel；　Ignorance；　are　flying　undisputed。　　We　are　not　making　a　reconnoissance　in　force；　still　less　advancing　with　the　main　column。　　But　here　are　a　few　roads　along　which　we　have　to　march　together；　and　we　wish　to　see　clearly　how　far　our　lines　extend；　and　where　the　enemy's　outposts　begin。

Before　touching　the　branches　of　knowledge　that　deal　with　organization　and　vital　functions；　let　us　glance　at　that　science　which　meets　you　at　the　threshold　of　your　study；　and　prepares　you　in　some　measure　to　deal　with　the　more　complex　problems　of　the　living　laboratory。


CHEMISTRY。　　includes　the　art　of　separating　and　combining　the　elements　of　matter；　and　the　study　of　the　changes　produced　by　these　operations。　We　can　hardly　say　too　much　of　what　it　has　contributed　to　our　knowledge　of　the　universe　and　our　power　of　dealing　with　its　materials。　　It　has　given　us　a　catalogue　raisonne　of　the　substances　found　upon　our　planet；　and　shown　how　everything　living　and　dead　is　put　together　from　them。　　It　is　accomplishing　wonders　before　us　every　day；　such　as　Arabian　story…tellers　used　to　string　together　in　their　fables。　　It　spreads　the；　sensitive　film　on　the　artificial　retina　which　looks　upon　us　through　the　optician's　lens　for　a　few　seconds；　and　fixes　an　image　that　will　outlive　its　original。　　It　questions　the　light　of　the　sun；　and　detects　the　vaporized　metals　floating　around　the　great　luminary；iron；　sodium；　lithium；　and　the　rest；as　if　the　chemist　of　our　remote　planet　could　fill　his　bell…glasses　from　its　fiery　atmosphere。　　It　lends　the　power　which　flashes　our　messages　in　thrills　that　leave　the　lazy　chariot　of　day　behind　them。　　It　seals　up　a　few　dark　grains　in　iron　vases；　and　lo！　at　the　touch　of　a　single　spark；　rises　in　smoke　and　flame　a　mighty　Afrit　with　a　voice　like　thunder　and　an　arm　that　shatters　like　an　earthquake。　　The　dreams　of　Oriental　fancy　have　become　the　sober　facts　of　our　every…day　life；　and　the　chemist　is　the　magician　to　whom　we　owe　them。

To　return　to　the　colder　scientific　aspect　of　chemistry。　　It　has　shown　us　how　bodies　stand　affected　to　each　other　through　an　almost　boundless　range　of　combinations。　　It　has　given　us　a　most　ingenious　theory　to　account　for　certain　fixed　relations　in　these　combinations。　It　has　successfully　eliminated　a　great　number　of　proximate　compounds；　more　or　less　stable；　from　organic　structures。　　It　has　invented　others　which　form　the　basis　of　long　series　of　well…known　composite　substances。　　In　fact；　we　are　perhaps　becoming　overburdened　with　our　list　of　proximate　principles；　demonstrated　and　hypothetical。

How　much　nearer　have　we　come　to　the　secret　of　force　than　Lully　and　Geber　and　the　whole　crew　of　juggling　alchemists？　　We　have　learned　a　great　deal　about　the　how；　what　have　we　learned　about　the　why？

Why　does　iron　rust；　while　gold　remains　untarnished；　and　gold　amalgamate；　while　iron　refuses　the　alliance　of　mercury？

The　alchemists　called　gold　Sol；　the　sun；　and　iron　Mars；　and　pleased　themselves　with　fancied　relations　between　these　substances　and　the　heavenly　bodies；　by　which　they　pretended　to　explain　the　facts　they　observed。　　Some　of　their　superstitions　have　lingered　in　practical　medicine　to　the　present　day；　but　chemistry　has　grown　wise　enough　to　confess　the　fact　of　absolute　ignorance。

What　is　it　that　makes　common　salt　crystallize　in　the　form　of　cubes；　and　saltpetre　in　the　shape　of　six…sided　prisms？　　We　see　no　reason　why　it　should　not　have　been　just　the　other　way；　salt　in　prisms　and　saltpetre　in　cubes；　or　why　either　should　take　an　exact　geometrical　outline；　any　more　than　coagulating　albumen。

But　although　we　had　given　up　attempting　to　explain　the　essential　nature　of　affinities　and　of　crystalline　types；　we　might　have　supposed　that　we　had　at　least　fixed　the　identity　of　the　substances　with　which　we　deal；　and　determined　the　laws　of　their　combination。　　All　at　once　we　find　that　a　simple　substance　changes　face；　puts　off　its　characteristic　qualities　and　resumes　them　at　will；not　merely　when　we　liquefy　or　vaporize　a　solid；　or　reverse　the　process；　but　that　a　solid　is　literally　transformed　into　another　solid　under　our　own　eyes。　We　thought　we　knew　phosphorus。　　We　warm　a　portion　of　it　sealed　in　an　empty　tube；　for　about　a　week。　　It　has　become　a　brown　infusible　substance；　which　does　not　shine　in　the　dark　nor　oxidate　in　the　air。　We　heat　it　to　500　F。；　and　it　becomes　common　phosphorus　again。　　We　transmute　sulphur　in　the　same　singular　way。　　Nature；　you　know；　gives　us　carbon　in　the　shape　of　coal　and　in　that　of　the　diamond。　　It　is　easy　to　call　these　changes　by　the　name　allotropism；　but　not　the　less　do　they　confound　our　hasty　generalizations。

These　facts　of　allotropism　have　some　corollaries　connected　with　them　rather　startling　to　us　of　the　nineteenth　century。　　There　may　be　other　transmutations　possible　besides　those　of　phosphorus　and　sulphur。　When　Dr。　Prout；　in　1840；　talked　about　azote　and　carbon　being　〃formed〃　in　the　living　system；　it　was　looked　upon　as　one　of　those　freaks　of　fancy　to　which　philosophers；　like　other　men；　are　subject。　　But　when　Professor　Faraday；　in　1851；　says；　at　a　meeting　of　the　British　Association；　that　〃his　hopes　are　in　the　direction　of　proving　that　bodies　called　simple　were　really　compounds；　and　may　be　formed　artificially　as　soon　as　we　are　masters　of　the　laws　influencing　their　combinations；〃when　he　comes　forward　and　says　that　he　has　tried　experiments　at　transmutation；　and　means；　if　his　life　is　spared；　to　try　them　again；how　can　we　be　surprised　at　the　popular　story　of　1861；　that　Louis　Napoleon　has　established　a　gold…factory　and　is　glutting　the　mints　of　Europe　with　bullion　of　his　own　making？

And　so　with　reference　to　the　law　of　combinations。　　The　old　maxim　was；　Corpora　non　agunt　nisi　soluta。　　If　two　substances；　a　and　b；　are　inclosed　in　a　glass　vessel；　c；　we　do　not　expect　the　glass　to　change　them；　unless　a　or　b　or　the　compound　a　b　has　the　power　of　dissolving　the　glass。　　But　if　for　a　I　take　oxygen；　for　b　hydrogen；　and　for