Dowegainanythingbyattemptingtogetridoftheideaofaspecialvitalforcebecausewefindcertainmutuallyconvertiblerelationsbetweenforcesinthebodyandoutofit？Ithinknot，anymorethanweshouldgainbygettingridoftheideaandexpressionMagnetismbecauseofitscorrelationwithelectricity。Wemayconcedetheunityofallformsofforce，butwecannotoverlookthefixeddifferencesofitsmanifestationsaccordingtotheconditionsunderwhichitacts。Itisamistake，however，tothinkthemysteryisgreaterinanorganizedbodythaninanyother。Weseeastonefalloracrystalform，andthereisnothingstrangerlefttowonderat，forwehaveseentheInfiniteinaction。
　　Justsofaraswecanrecognizetheordinarymodesofoperationofthecommonforcesofnature，——gravity，cohesion，elasticity，transudation，chemicalaction，andtherest，——weseetheso-calledvitalactsinthelightofalargerrangeofknownfactsandfamiliaranalogies。Matteuecci’swell-rememberedlecturescontainmanyandstrikingexamplesoftheworkingofphysicalforcesinphysiologicalprocesses。Whereverrigidexperimentcarriesus，wearesafeinfollowingthislead；butthemomentwebegintotheorizebeyondourstrictobservation，weareindangeroffallingintothosemechanicalfollieswhichtruesciencehaslongoutgrown。
　　Recognizingthefact，then，thatwehavelearnednothingbutthemachineryoflife，andarenonearertoitsessence，whatisitthatwehavegainedbythisgreatdiscoveryofthecellformationandfunction？
　　ItwouldhavebeenrewardenoughtolearnthemethodNaturepursuesforitsownsake。IfthesovereignArtificerletsusintohisownlaboratoriesandworkshops，weneednotaskmorethantheprivilegeoflookingonathiswork。Wedonotknowwherewenowstandinthehierarchyofcreatedintelligences。Weweremadealittlelowerthantheangels。Ispeakitnotirreverently；astheloweranimalssurpassmaninsomeoftheirattributes，soitmaybethatnoteveryangel’seyecanseeasbroadlyandasdeeplyintothematerialworksofGodasmanhimself，lookingatthefirmamentthroughanequatorialoffifteeninches’aperture，andsearchingintothetissueswithatwelfthofaninchobjective。
　　Butthereareotherpositivegainsofamorepracticalcharacter。
　　Thuswearenolongerpermittedtoplacetheseatofthelivingactionsintheextremevessels，whichareonlythecarriersfromwhicheachparttakeswhatitwantsbythedivinerightoftheomnipotentnucleatedcell。Theorganismhasbecome，inthewordsalreadyborrowedfromVirchow，“asumofvitalunities。“Thestrictumandlaxum，theincreasedanddiminishedactionofthevessels，outofwhichmedicaltheoriesandmethodsoftreatmenthavegrownup，haveyieldedtothedoctrineoflocalcell-communities，belongingtothisorthatvasculardistrict，fromwhichtheyhelpthemselves，ascontractorsarewonttodofromthenationaltreasury。
　　Icannotpromisetodomorethantoselectafewofthepointsofcontactbetweenourignoranceandourknowledgewhichpresentparticularinterestintheexistingstateofourphysiologicalacquisitions。SomeoftheminvolvethemicroscopicdiscoveriesofwhichIhavebeenspeaking，somebelongtothedomainofchemistry，andsomehaverelationswithotherdepartmentsofphysicalscience。
　　Ifweshouldbeginwiththedigestivefunction，weshouldfindthatthelong-agitatedquestionofthenatureoftheacidofthegastricjuiceisbecomingsettledinfavorofthelactic。Butthewholesolventagencyofthedigestivefluidentersintothecategoryofthatexceptionalmodeofactionalreadyfamiliartousinchemistryascatalysis。Itisthereforedoublydifficultofexplanation；
　　first，asbeing，likeallreactions，afactnottobeaccountedforexceptbytheimaginativeappealto“affinity，“andsecondly，asbeingoneofthosepeculiarreactionsprovokedbyanelementwhichstandsoutsideandlooksonwithoutcompromisingitself。
　　ThedoctrineofMulder，sowidelydiffusedinpopularandscientificbelief，oftheexistenceofacommonbaseofallalbuminoussubstances，theso-calledprotein，hasnotstoodthetestofrigorousanalysis。Thedivisionoffoodintoazotizedandnon-azotizedisnodoubtimportant，buttheattempttoshowthatthefirstonlyisplasticornutritive，whilethesecondissimplycalorifacient，orheat-producing，failsentirelyinthefaceofthefactsrevealedbythestudyofmanindifferentclimates，andofnumerousexperimentsinthefeedingofanimals。Imustreturntothissubjectinconnectionwiththerespiratoryfunction。
　　Thesugar-makingfacultyoftheliverisanother“catalytic“mystery，asgreatastherestofthem，andnogreater。Liver-tissuebringssugaroutoftheblood，oroutofitsownsubstance；——why？
　　QuiaestineoVirtussaccharitiva。
　　Justwhatbecomesofthesugarbeyondthefactofitsdisappearancebeforeitcangetintothegeneralcirculationandsweetenourtempers，itishardtosay。
　　Thepancreaticfluidmakesanemulsionofthefatcontainedinourfood，butjusthowthefattyparticlesgetintothevilliwemustleaveBruckeandKollikertosettleiftheycan。
　　Noonehasshownsatisfactorilytheprocessbywhichtheblood-
　　corpusclesareformedoutofthelymph-corpuscles，norwhatbecomesofthem。Thesetwoquestionsarelikethosefamoushouseholdpuzzles，——Wheredothefliescomefrom？and，Wheredothepinsgoto？
　　Thereisaseriesoforgansinthebodywhichhaslongpuzzledphysiologists，——organsofglandularaspect，buthavingnoducts，——thespleen，thethyroidandthymusbodies，andthesuprarenalcapsules。
　　Wecallthemvascularglands，andwebelievethattheyelaboratecoloredanduncoloredblood-cells；butjustwhatchangestheyeffect，andjusthowtheyeffectthem，ithasprovedaverydifficultmattertodetermine。SoofthenotedglanduleswhichformPeyer’spatches，theirpreciseoffice，thoughseeminglylikethoseofthelymphaticglands，cannotbepositivelyassigned，sofarasIknow，atthepresenttime。Itisofobviousinteresttolearnitwithreferencetothepathologyoftyphoidfever。Itwillberemarkedthatthecoincidenceoftheirchangesinthisdiseasewithenlargementofthespleensuggeststheideaofasimilarityoffunctioninthesetwoorgans。
　　Thetheoriesoftheproductionofanimalheat，fromthetimesofBlack，Lavoisier，andCrawfordtothoseofLiebig，arefamiliartoallwhohavepaidanyattentiontophysiologicalstudies。ThesimplicityofLiebig’sviews，andthepopularforminwhichtheyhavebeenpresented，havegiventhemwidecurrency，andincorporatedtheminthecommonbeliefandlanguageofourtext-books。Directoxidationorcombustionofthecarbonandhydrogencontainedinthefood，orinthetissuesthemselves；thedivisionofalimentarysubstancesintorespiratory，ornon-azotized，andazotized，——thesedoctrinesarefamiliareventotheclassesinourhigh-schools。Butthissimplestatementisboldlyquestioned。Nothingprovesthatoxygencombinesinthesystemwithhydrogenandcarboninparticular，ratherthanwithsulphurandazote。Suchisthewell-
　　groundedstatementofRobinandVerdeil。“Itisveryprobablethatanimalheatisentirelyproducedbythechemicalactionswhichtakeplaceintheorganism，butthephenomenonistoocomplextoadmitofourcalculatingitaccordingtothequalityofoxygenconsumed。“
　　TheselastarethewordsofRegnault，ascitedbyMr。Lewes，whoseintelligentdiscussionofthisandmanyofthemostinterestingphysiologicalproblemsIstronglyrecommendtoyourattention。
　　Thissingleillustrationcoversawidergroundthanthespecialfunctiontowhichitbelongs。Wearelearningthatthechemistryofthebodymustbestudied，notsimplybyitsingestaandegesta，butthatthereisalongintermediateseriesofchangeswhichmustbeinvestigatedintheirownlight，undertheirownspecialconditions。
　　Theexpression“sumofvitalunities“appliestothechemicalactions，aswellastootheractionslocalizedinspecialparts；andwhenthedistinguishedchemistswhomIhavejustcitedentitletheirworkatreatiseontheimmediateprinciplesofthebody，theyonlyindicatethenatureofthatprofoundandsubtileanalysiswhichmusttaketheplaceofallhastygeneralizationsfoundedonacomparisonofthefoodwithresidualproducts。
　　Iwillonlycallyourattentiontothefact，thattheexceptionalphenomenonofthelaboratoryistheprevailinglawoftheorganism。
　　Nutritionitselfisbutonegreatcatalyticprocess。Asthebloodtravelsitsrounds，eachpartselectsitsappropriateelementandtransformsittoitsownlikeness。Whethertheappropriatingagentbecellornucleus，orastructurelesssolidliketheintercellularsubstanceofcartilage，thefactofitspresencedeterminestheseparationofitsproperconstituentsfromthecirculatingfluid，sothatevenwhenwearewoundedboneisreplacedbybone，skinbyskin，andnervebynerve。
　　Itishardlywithoutasmilethatweresuscitatetheoldquestionofthevisinsitaofthemuscularfibre，sofamousinthediscussionsofHallerandhiscontemporaries。Speakinggenerally，IthinkwemaysaythatHaller’sdoctrineistheonenowcommonlyreceived；namely，thatthemusclescontractinvirtueoftheirowninherentendowments。
　　ItistruethatKollikersaysnoperfectlydecisivefacthasbeenbroughtforwardtoprovethatthestriatedmusclescontractwith。
　　outhavingbeenactedonbynerves。YetMr。Bowman’sobservationsonthecontractionofisolatedfibresappeardecisiveenoughunlessweconsidertheminvalidatedbyDr。LionelBeale’srecentresearches，tendingtoshowthateachelementaryfibreissuppliedwithnerves；
　　andastothesmoothmuscularfibres，wehaveVirchow’sstatementrespectingthecontractilityofthoseoftheumbilicalcord，wherethereisnotatraceofanynerves。
　　Intheinvestigationofthenervoussystem，anatomyandphysiologyhavegonehandinhand。Itisverysingularthatsoimportant，andseeminglysimple，afactastheconnectionofthenerve-tubes，attheiroriginorintheircourse，withthenerve-cells，shouldhavesolongremainedopentodoubt，asyoumayseethatitdidbyreferringtotheverycompleteworkofSharpeyandQuaineditionof1849，thehistologicalportionofwhichiscordiallyapprovedbyKollikerhimself。
　　SeveralmostinterestingpointsoftheminuteanatomyofthenervouscentreshavebeenlaboriouslyandskilfullyworkedoutbyarecentgraduateofthisMedicalSchool，inamonographworthytostandinlinewiththoseofLockhartClarke，Stilling，andSchrodervanderKolk。IhavehadtheprivilegeofexaminingandofshowingsomeofyouanumberofDr。Dean’sskilfulpreparations。Ihavenospacetogiveevenanabstractofhisconclusions。Icanonlyrefertohisproofofthefact，thatasinglecellmaysenditsprocessesintoseveraldifferentbundlesofnerve-roots，andtohisdemonstrationofthecurvedascendinganddescendingfibresfromtheposteriornerveroots，toreachwhathehascalledthelongitudinalcolumnsofthecornea。ImustalsomentionDr。Dean’sexquisitemicroscopicphotographsfromsectionsofthemedullaoblongata，whichappeartometopromiseanewdevelopment，ifnotanewepoch，inanatomicalart。
　　Ithavingbeensettledthatthenerve-tubescanverycommonlybetraceddirectlytothenerve-cells，theobjectofalltheobserversinthisdepartmentofanatomyistofollowthesetubestotheirorigin。Wehaveaninfinitesnarloftelegraphwires，andwemaybereasonablysure，that，ifwecanfollowthemup，weshallfindeachofthemendsinabatterysomewhere。Oneofthemostinterestingproblemsistofindtheganglionicoriginofthegreatnervesofthemedullaoblongata，andthisistheendtowhich，bytheaidofthemostdelicatesections，coloredsoastobringouttheirdetails，mountedsoastobeimperishable，magnifiedbythebestinstruments，andnowself-recordedinthelightofthetruth-tellingsunbeam，ourfellow-studentismakingasteadyprogressinalaborwhichIthinkbidsfairtorankwiththemostvaluablecontributionstohistologythatwehavehadfromthissideoftheAtlantic。
　　Itisinterestingtoseehowoldquestionsareincidentallysettledinthecourseofthesenewinvestigations。Thus，Mr。Clarke’sdissections，confirmedbypreparationsofMr。Dean’swhichIhavemyselfexamined，placedthefactofthedecussationofthepyramids——
　　deniedbyHaller，byMorgagni，andevenbyStilling——beyonddoubt。
　　Sothespinalcanal，theexistenceofwhich，atleastintheadult，hasbeensooftendisputed，appearsasacoarseandunequivocalanatomicalfactinmanyofthepreparationsreferredto。