medical essays-第42部分

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t　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　c　a　piece　of　spongy　platinum；　I　find　the　first　two　combine　with　the　common　signs　of　combustion　and　form　water；　the　third　in　the　mean　time　undergoing　no　perceptible　change。　　It　has　played　the　part　of　the　unwedded　priest；　who　marries　a　pair　without　taking　a　fee　or　having　any　further　relation　with　the　parties。　　We　call　this　catalysis；　catalytic　action；　the　action　of　presence；　or　by　what　learned　name　we　choose。　　Give　what　name　to　it　we　will；　it　is　a　manifestation　of　power　which　crosses　our　established　laws　of　combination　at　a　very　open　angle　of　intersection。　　I　think　we　may　find　an　analogy　for　it　in　electrical　induction；　the　disturbance　of　the　equilibrium　of　the　electricity　of　a　body　by　the　approach　of　a　charged　body　to　it；　without　interchange　of　electrical　conditions　between　the　two　bodies。　But　an　analogy　is　not　an　explanation；　and　why　a　few　drops　of　yeast　should　change　a　saccharine　mixture　to　carbonic　acid　and　alcohol；a　little　leaven　leavening　the　whole　lump；not　by　combining　with　it；　but　by　setting　a　movement　at　work；　we　not　only　cannot　explain；　but　the　fact　is　such　an　exception　to　the　recognized　laws　of　combination　that　Liebig　is　unwilling　to　admit　the　new　force　at　all　to　which　Berzelius　had　given　the　name　so　generally　accepted。

The　phenomena　of　isomerism；　or　identity　of　composition　and　proportions　of　constituents　with　difference　of　qualities；　and　of　isomorphism；　or　identity　of　form　in　crystals　which　have　one　element　substituted　for　another；　were　equally　surprises　to　science；　and　although　the　mechanism　by　which　they　are　brought　about　can　be　to　a　certain　extent　explained　by　a　reference　to　the　hypothetical　atoms　of　which　the　elements　are　constituted；　yet　this　is　only　turning　the　difficulty　into　a　fraction　with　an　infinitesimal　denominator　and　an　infinite　numerator。

So　far　we　have　studied　the　working　of　force　and　its　seeming　anomalies　in　purely　chemical　phenomena。　　But　we　soon　find　that　chemical　force　is　developed　by　various　other　physical　agencies；by　heat；　by　light；　by　electricity；　by　magnetism；　by　mechanical　agencies；　and；　vice　versa；　that　chemical　action　develops　heat；　light；　electricity；　magnetism；　mechanical　force；　as　we　see　in　our　matches；　galvanic　batteries；　and　explosive　compounds。　　Proceeding　with　our　experiments；　we　find　that　every　kind　of　force　is　capable　of　producing　all　other　kinds；　or；　in　Mr。　Faraday's　language；　that　〃the　various　forms　under　which　the　forces　of　matter　are　made　manifest　have　a　common　origin；　or；　in　other　words；　are　so　directly　related　and　mutually　dependent　that　they　are　convertible　one　into　another。〃

Out　of　this　doctrine　naturally　springs　that　of　the　conservation　of　force；　so　ably　illustrated　by　Mr。　Grove；　Dr。　Carpenter；　and　Mr。　Faraday。　　This　idea　is　no　novelty；　though　it　seems　so　at　first　sight。　It　was　maintained　and　disputed　among　the　giants　of　philosophy。　Des　Cartes　and　Leibnitz　denied　that　any　new　motion　originated　in　nature；　or　that　any　ever　ceased　to　exist；　all　motion　being　in　a　circle；　passing　from　one　body　to　another；　one　losing　what　the　other　gained。　　Newton；　on　the　other　hand；　believed　that　new　motions　were　generated　and　existing　ones　destroyed。　　On　the　first　supposition；　there　is　a　fixed　amount　of　force　always　circulating　in　the　universe。　On　the　second；　the　total　amount　may　be　increasing　or　diminishing。　You　will　find　in　the　〃Annual　of　Scientific　Discovery〃　for　1858　a　very　interesting　lecture　by　Professor　Helmholtz　of　Bonn；　in　which　it　is　maintained　that　a　certain　portion　of　force　is　lost　in　every　natural　process；　being　converted　into　unchangeable　heat；　so　that　the　universe　will　come　to　a　stand…still　at　last；　all　force　passing　into　heat；　and　all　heat　into　a　state　of　equilibrium。

The　doctrines　of　the　convertibility　or　specific　equivalence　of　the　various　forms　of　force；　and　of　its　conservation；　which　is　its　logical　consequence；　are　very　generally　accepted；　as　I　believe；　at　the　present　time；　among　physicists。　　We　are　naturally　led　to　the　question；　What　is　the　nature　of　force？　　The　three　illustrious　philosophers　just　referred　to　agree　in　attributing　the　general　movements　of　the　universe　to　th