a history of science-4-第16章

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BICHAT　AND　THE　BODILY　TISSUES

Much　the　same　thing　may　be　said　of　another　generalization　regarding　the　animal　body；　which　the　brilliant　young　French　physician　Marie　Francois　Bichat　made　in　calling　attention　to　the　fact　that　each　vertebrate　organism；　including　man；　has　really　two　quite　different　sets　of　organsone　set　under　volitional　control；　and　serving　the　end　of　locomotion；　the　other　removed　from　volitional　control；　and　serving　the　ends　of　the　〃vital　processes〃　of　digestion；　assimilation；　and　the　like。　He　called　these　sets　of　organs　the　animal　system　and　the　organic　system；　respectively。　　The　division　thus　pointed　out　was　not　quite　new；　for　Grimaud；　professor　of　physiology　in　the　University　of　Montpellier；　had　earlier　made　what　was　substantially　the　same　classification　of　the　functions　into　〃internal　or　digestive　and　external　or　locomotive〃；　but　it　was　Bichat's　exposition　that　gave　currency　to　the　idea。

Far　more　important；　however；　was　another　classification　which　Bichat　put　forward　in　his　work　on　anatomy；　published　just　at　the　beginning　of　the　last　century。　　This　was　the　division　of　all　animal　structures　into　what　Bichat　called　tissues；　and　the　pointing　out　that　there　are　really　only　a　few　kinds　of　these　in　the　body；　making　up　all　the　diverse　organs。　Thus　muscular　organs　form　one　system；　membranous　organs　another；　glandular　organs　a　third；　the　vascular　mechanism　a　fourth；　and　so　on。　　The　distinction　is　so　obvious　that　it　seems　rather　difficult　to　conceive　that　it　could　have　been　overlooked　by　the　earliest　anatomists；　but；　in　point　of　fact；　it　is　only　obvious　because　now　it　has　been　familiarly　taught　for　almost　a　century。　It　had　never　been　given　explicit　expression　before　the　time　of　Bichat；　though　it　is　said　that　Bichat　himself　was　somewhat　indebted　for　it　to　his　master；　Desault；　and　to　the　famous　alienist　Pinel。

However　that　may　be；　it　is　certain　that　all　subsequent　anatomists　have　found　Bichat's　classification　of　the　tissues　of　the　utmost　value　in　their　studies　of　the　animal　functions。　Subsequent　advances　were　to　show　that　the　distinction　between　the　various　tissues　is　not　really　so　fundamental　as　Bichat　supposed；　but　that　takes　nothing　from　the　practical　value　of　the　famous　classification。

It　was　but　a　step　from　this　scientific　classification　of　tissues　to　a　similar　classification　of　the　diseases　affecting　them；　and　this　was　one　of　the　greatest　steps　towards　placing　medicine　on　the　plane　of　an　exact　science。　This　subject　of　these　branches　completely　fascinated　Bichat；　and　he　exclaimed；　enthusiastically：　　〃Take　away　some　fevers　and　nervous　trouble；　and　all　else　belongs　to　the　kingdom　of　pathological　anatomy。〃　But　out　of　this　enthusiasm　came　great　results。　　Bichat　practised　as　he　preached；　and；　believing　that　it　was　only　possible　to　understand　disease　by　observing　the　symptoms　carefully　at　the　bedside；　and；　if　the　disease　terminated　fatally；　by　post…mortem　examination；　he　was　so　arduous　in　his　pursuit　of　knowledge　that　within　a　period　of　less　than　six　months　he　had　made　over　six　hundred　autopsiesa　record　that　has　seldom；　if　ever；　been　equalled。　Nor　were　his　efforts　fruitless；　as　a　single　example　will　suffice　to　show。　By　his　examinations　he　was　able　to　prove　that　diseases　of　the　chest；　which　had　formerly　been　classed　under　the　indefinite　name　〃peripneumonia；〃　might　involve　three　different　structures；　the　pleural　sac　covering　the　lungs；　the　lung　itself；　and　the　bronchial　tubes；　the　diseases　affecting　these　organs　being　known　respectively　as　pleuritis；　pneumonia；　and　bronchitis；　each　one　differing　from　the　others　as　to　prognosis　and　treatment。　The　advantage　of　such　an　exact　classification　needs　no　demonstration。


LISTER　AND　THE　PERFECTED　MICROSCOPE

At　the　same　time　when　these　broad　macroscopical　distinctions　were　being　drawn　there　were　other　workers　who　were　striving　to　go　even　deeper　into　the　intricacies　of　the　animal　mechanism　with　the　aid　of　the　microscope。　　This　undertaking；　however；　was　beset　with　very　great　optical　difficulties；　and　for　a　long　time　little　advance　was　made　upon　the　work　of　preceding　generations。　Two　great　optical　barriers；　known　technically　as　spherical　and　chromatic　aberrationthe　one　due　to　a　failure　of　the　rays　of　light　to　fall　all　in　one　plane　when　focalized　through　a　lens；　the　other　due　to　the　dispersive　action　of　the　lens　in　breaking　the　white　light　into　prismatic　colorsconfronted　the　makers　of　microscopic　lenses；　and　seemed　all　but　insuperable。　The　making　of　achromatic　lenses　for　telescopes　had　been　accomplished；　it　is　true；　by　Dolland　in　the　previous　century；　by　the　union　of　lenses　of　crown　glass　with　those　of　flint　glass；　these　two　materials　having　different　indices　of　refraction　and　dispersion。　But；　aside　from　the　mechanical　difficulties　which　arise　when　the　lens　is　of　the　minute　dimensions　required　for　use　with　the　microscope；　other　perplexities　are　introduced　by　the　fact　that　the　use　of　a　wide　pencil　of　light　is　a　desideratum；　in　order　to　gain　sufficient　illumination　when　large　magnification　is　to　be　secured。

In　the　attempt　to　overcome　those　difficulties；　the　foremost　physical　philosophers　of　the　time　came　to　the　aid　of　the　best　opticians。　Very　early　in　the　century；　Dr。　（afterwards　Sir　David）　Brewster；　the　renowned　Scotch　physicist；　suggested　that　certain　advantages　might　accrue　from　the　use　of　such　gems　as　have　high　refractive　and　low　dispersive　indices；　in　place　of　lenses　made　of　glass。　Accordingly　lenses　were　made　of　diamond；　of　sapphire；　and　so　on；　and　with　some　measure　of　success。　　But　in　1812　a　much　more　important　innovation　was　introduced　by　Dr。　William　Hyde　Wollaston；　one　of　the　greatest　and　most　versatile；　and；　since　the　death　of　Cavendish；　by　far　the　most　eccentric　of　English　natural　philosophers。　This　was　the　suggestion　to　use　two　plano…convex　lenses；　placed　at　a　prescribed　distance　apart；　in　lieu　of　the　single　double…convex　lens　generally　used。　　This　combination　largely　overcame　the　spherical　aberration；　and　it　gained　immediate　fame　as　the　〃Wollaston　doublet。〃

To　obviate　loss　of　light　in　such　a　doublet　from　increase　of　reflecting　surfaces；　Dr。　Brewster　suggested　filling　the　interspace　between　the　two　lenses　with　a　cement　having　the　same　index　of　refraction　as　the　lenses　themselvesan　improvement　of　manifest　advantage。　An　improvement　yet　more　important　was　made　by　Dr。　Wollaston　himself　in　the　introduction　of　the　diaphragm　to　limit　the　field　of　vision　between　the　lenses；　instead　of　in　front　of　the　anterior　lens。　　A　pair　of　lenses　thus　equipped　Dr。　Wollaston　called　the　periscopic　microscope。　Dr。　Brewster　suggested　that　in　such　a　lens　the　same　object　might　be　attained　with　greater　ease　by　grinding　an　equatorial　groove　about　a　thick　or　globular　lens　and　filling　the　groove　with　an　opaque　cement。　This　arrangement　found　much　favor；　and　came　subsequently　to　be　known　as　a　Coddington　lens；　though　Mr。　Coddington　laid　no　claim　to　being　its　inventor。

Sir　John　Herschel；　another　of　the　very　great　physicists　of　the　time；　also　gave　attention　to　the　problem　of　improving　the　microscope；　and　in　1821　he　introduced　what　was　called　an　aplanatic　combination　of　lenses；　in　which；　as　the　name　implies；　the　spherical　aberration　was　largely　done　away　with。　It　was　thought　that　the　use　of　this　Herschel　aplanatic　combination　as　an　eyepiece；　combined　with　the　Wollaston　doublet　for　the　objective；　came　as　near　perfection　as　the　compound　microscope　was　likely　soon　to　come。　But　in　reality　the　instrument　thus　constructed；　though　doubtless　superior　to　any　predecessor；　was　so　defective　that　for　practical　purposes　the　simple　microscope；　such　as　the　doublet　or　the　Coddington；　was　preferable　to　the　more　complicated　one。

Many　opticians；　indeed；　quite　despaired　of　ever　being　able　to　make　a　satisfactory　refracting　compound　microscope；　and　some　of　them　had　taken　up　anew　Sir　Isaac　Newton's　suggestion　in　reference　to　a　reflecting　microscope。　　In　particular；　Professor　Giovanni　Battista　Amici；　a　very　famous　mathematician　and　practical　optician　of　Modena；　succeeded　in　constructing　a　reflecting　microscope　which　was　said　to　be　superior　to　any　compound　microscope　of　the　time；　though　the　events　of　the　ensuing　years　were　destined　to　rob　it　of　all　but　historical　value。　For　there　were　others；　fortunately；　who　did　not　despair　of　the　possibilities　of　the　refracting　microscope；　and　their　efforts　were　destined　before　long　to　be　crowned　with　a　degree　of　success　not　even　dreamed　of　by　any　preceding　generation。

The　man　to　whom　chief　credit　is　due　for　directing　those　final　steps　that　made　the　compound　microscope　a　practical　implement　instead　of　a　scientific　toy　was　the　English　amateur　optician　Joseph　Jackson　Lister。　　Combining　mathematical　knowledge　with　mechanical　ingenuity；　and　having　the　practical　aid　of　the　celebrated　optician　Tulley；　he　devised　formulae　for　the　combination　of　lenses　of　crown　glass　with　others　of　flint　glass；　so　adjusted　that　the　refractive　errors　of　one　were　corrected　or　compensated　by　the　other；　with　the　result　of　producing　lenses　of　hitherto　unequalled　powers　of　definition；　lenses　capable　of　showing　an　image　highly　magnified；　yet　relatively　free　from　those　distortions　and　fringes　of　color　that　had　heretofore　been　so　disastrous　to　true　interpretation　of　magnified　structures。

Lister　had　begun　his　studies　of　the　lens　in　1824；　but　it　was　not　until　1830　that　he　contributed　to　the　Royal　Society　the　famous　paper　detailing　his　theories　and　experiments。　Soon　after　this　various　continental　opticians　who　had　long　been　working　along　similar　lines　took　the　matter　up；　and　their　expositions；　in　particular　that　of　Amici；　introduced　the　improved　compound　microscope　to　the　attention　of　microscopists　everywhere。　And　it　required　but　the　most　casual　trial　to　convince　the　experienced　observers　that　a　new　implement　of　scientific　research　had　been　placed　in　their　hands　which　carried　them　a　long　step　nearer　the　observation　of　the　intimate　physical　processes　which　lie　at　the　foundation　of　vital　phenomena。　　For　the　physiologist　this　perfection　of　the　compound　microscope　had　the　same　significance　that　the；　discovery　of　America　had　for　the　fifteenth…century　geographersit　promised　a　veritable　world　of　utterly　novel　revelations。　Nor　was　the　fulfilment　of　that　promise　long　delayed。

Indeed；　so　numerous　and　so　important　were　the　discoveries　now　made　in　the　realm　of　minute　anatomy　that　the　rise　of　histology　to　the　rank　of　an　independent　science　may　be　said　to　date　from　this　period。　Hitherto；　ever　since　the　discovery　of　magnifying…glasses；　there　had　been　here　and　there　a　man；　such　as　Leuwenhoek　or　Malpighi；　gifted　with　exceptional　vision；　and　perhaps　unusually　happy　in　his　conjectures；　who　made　important　contributions　to　the　knowledge　of　the　minute　structure　of　organic　tissues；　but　now　of　a　sudden　it　became　possible　for　the　veriest　tyro　to　confirm　or　refute　the　laborious　observations　of　these　pioneers；　while　the　skilled　observer　could　step　easily　beyond　the　barriers　of　vision　that　hitherto　were　quite　impassable。　And　so；　naturally　enough；　the　physiologists　of　the　fourth　decade　of　the　nineteenth　century　rushed　as　eagerly　into　the　new　realm　of　the　microscope　as；　for　example；　their　successors　of　to…day　are　exploring　the　realm　of　the　X…ray。

Lister　himself；　who　had　become　an　eager　interrogator　of　the　instrument　he　had　perfected；　made　many　imp