thesesimpleformulaebywhichwecondensetheobservationsofagenerationinasingleaxiom；theselogicalanalysesbywhichwefenceouttheignorancewecannotreclaim，andfixthelimitsofourknowledge，——allleadusuptotheinspirationoftheAlmighty，whichgivesunderstandingtotheworld’sgreatteachers。Tofearscienceorknowledge，lestitdisturbouroldbeliefs，istofeartheinfluxoftheDivinewisdomintothesoulsofourfellow-men；forwhatissciencebutthepiecemealrevelation，——uncovering，——oftheplanofcreation，bytheagencyofthosechosenprophetsofnaturewhomGodhasilluminatedfromthecentrallightoftruthforthatsinglepurpose？
　　Thestudieswhichwehaveglancedatarepreliminaryinyoureducationtothepracticalartswhichmakeuseofthem，——theartsofhealing，——surgeryandmedicine。Themoreyouexaminethestructureoftheorgansandthelawsoflife，themoreyouwillfindhowresolutelyeachofthecell-republicswhichmakeuptheEpluribusunumofthebodymaintainsitsindependence。Guardit，feedit，airit，warmit，exerciseorrestitproperly，andtheworkingelementswilldotheirbesttokeepwellortogetwell。Whatdowedowithailingvegetables？Dr。Warren，myhonoredpredecessorinthischair，boughtacountry-place，includinghalfofanoldorchard。AfewyearsafterwardsIsawthetreesonhissideofthefencelookingingoodhealth，whilethoseontheothersidewerescraggyandmiserable。Howdoyousupposethischangewasbroughtabout？BywateringthemwithFowler’ssolution？Bydiggingincalomelfreelyabouttheirroots？Notatall；butbylooseningthesoilroundthem，andsupplyingthemwiththerightkindoffoodinfittingquantities。
　　Nowamanisnotaplant，or，atleast，heisaverycuriousone，forhecarrieshissoilinhisstomach，whichisakind——ofportableflower-pot，andhegrowsroundit，insteadofoutofit。Hehas，besides，asingularlycomplexnutritiveapparatusandanervoussystem。ButrecollectthedoctrinealreadyenunciatedinthelanguageofVirchow，thatananimal，likeatree，isasumofvitalunities，ofwhichthecellistheultimateelement。Everyhealthycell，whetherinavegetableorananimal，necessarilyperformsitsfunctionproperlysolongasitissuppliedwithitspropermaterialsandstimuli。Acellmay，itistrue，becongenitallydefective，inwhichcasediseaseis，sotospeak，itsnormalstate。Butiforiginallysoundandsubsequentlydiseased，therehascertainlybeensomeexcess，deficiency，orwrongqualityinthematerialsorstimuliappliedtoit。Youremovethisinjuriousinfluenceandsubstituteanormalone；removethebakedcoal-ashes，forinstance，fromtherootsofatree，andreplacethemwithloam；takeawaythesaltmeatfromthepatient’stable，andreplaceitwithfreshmeatandvegetables，andthecellsofthetreeorthemanreturntotheirduty。
　　Idonotknowthatweeverapplytoaplantanyelementwhichisnotanaturalconstituentofthevegetablestructure，exceptperhapsexternally，fortheaccidentalpurposeofkillingparasites。Thewholeartofcultivationconsistsinlearningtheproperfoodandconditionsofplants，andsupplyingthem。Wegivethemwater，earths，saltsofvariouskindssuchastheyaremadeof，withachancetohelpthemselvestoairandlight。Thefarmerwouldbelaughedatwhoundertooktomanurehisfieldsorhistreeswithasaltofleadorofarsenic。Theseelementsarenotconstituentsofhealthyplants。Thegardenerusesthewasteofthearsenicfurnacestokilltheweedsinhiswalks。
　　Ifthelawoftheanimalcell，andoftheanimalorganism，whichisbuiltupofsuchcells，islikethatofthevegetable，wemightexpectthatweshouldtreatallmorbidconditionsofanyofthevitalunitiesbelongingtoananimalinthesameway，byincreasing，diminishing，orchangingitsnaturalfoodorstimuli。
　　“Thatisanalimentwhichnourishes；whateverwefindintheorganism，asaconstantandintegralelement，eitherformingpartofitsstructure，oroneoftheconditionsofvitalprocesses，thatandthatonlydeservesthenameofaliment。““Iseenoreason，therefore，whyiron，phosphateoflime，sulphur，shouldnotbeconsideredfoodforman，asmuchasguanoorpoudretteforvegetables。Whetheroneoranotherofthemisbestinanygivencase，——whethertheyshallbetakenaloneorincombination，inlargeorsmallquantities，areseparatequestions。Buttheyareelementsbelongingtothebody，andeveninmoderateexcesswillproducelittledisturbance。Thereisnopresumptionagainstanyofthisclassofsubstances，anymorethanagainstwaterorsalt，providedtheyareusedinfittingcombinations，proportions，andforms。
　　Butwhenitcomestosubstancesalientothehealthysystem，whichneverbelongtoitasnormalconstituents，thecaseisverydifferent。Thereisapresumptionagainstputtingleadorarsenicintothehumanbody，asagainstputtingthemintoplants，becausetheydonotbelongthere，anymorethanpoundedglass，which，itissaid，usedtobegivenasapoison。Thesamethingistrueofmercuryandsilver。Whatbecomesofthesealiensubstancesaftertheygetintothesystemwecannotalwaystell。Butinthecaseofsilver，fromtheaccidentofitschangingcolorundertheinfluenceoflight，wedoknowwhathappens。Itisthrownout，inpartatleast，undertheepidermis，andthereitremainstothepatient’sdyingday。Thisisastrikingillustrationofthedifficultywhichthesystemfindsindealingwithnon-assimilableelements，andjustifiesinsomemeasurethevulgarprejudiceagainstmineralpoisons。“
　　Itrusttheyoungeststudentonthesebencheswillnotcommitthechildisherrorofconfoundingapresumptionagainstaparticularclassofagentswithacondemnationofthem。Mercury，forinstance，isalientothesystem，andeminentlydisturbinginitsinfluence。
　　Yetitsefficacyincertainformsofspecificdiseaseisacknowledgedbyallbutthemostscepticaltheorists。EventheespritmoqueurofRicord，theVoltaireofpelvicliterature，submitstothetime-
　　honoredconstitutionalauthorityofthisgreatpanaceaintheclassofcasestowhichhehasdevotedhisbrilliantintelligence。Still，thereisnotellingwhatevilshavearisenfromtheabuseofthismineral。Dr。Armstronglongagopointedoutsomeofthem，andtheyhavebecomemattersofcommonnotoriety。Iampleased，therefore，whenIfindsoableandexperiencedapractitionerasDr。Williamsofthiscityprovingthatiritisisbesttreatedwithoutmercury，andDr。Vanderpoelshowingthesamethingtobetrueforpericarditis。
　　Whateverelementsnaturedoesnotintroduceintovegetables，thenaturalfoodofallanimallife，——directlyofherbivorous，indirectlyofcarnivorousanimals，——aretoberegardedwithsuspicion。Arsenic-
　　eatingmayseemtoimprovetheconditionofhorsesforatime，——andevenofhumanbeings，ifTschudi’sstoriescanbetrusted，——butitsoonappearsthatitsalienqualitiesareatwarwiththeanimalorganization。Soofcopper，antimony，andothernon-alimentarysimplesubstances；everyoneofthemisanintruderinthelivingsystem，asmuchasaconstablewouldbe，quarteredinourhousehold。
　　Thisdoesnotmeanthattheymaynot，anyofthem，becalledinforaspecialneed，aswesendfortheconstablewhenwehavegoodreasontothinkwehaveathiefunderourroof；butaman’sbodyishiscastle，aswellashishouse，andthepresumptionisthatwearetokeepouralimentarydoorsboltedagainsttheseperturbingagents。
　　Nowthefeelingisveryapttobejustcontrarytothis。Thehabithasbeenverygeneralwithwell-taughtpractitioners，tohaverecoursetotheintroductionofthesealienelementsintothesystemontheoccasionofanyslightdisturbance。Thetonguewasalittlecoated，andmercurymustbegiven；theskinwasalittledry，andthepatientmusttakeantimony。Itwaslikesendingfortheconstableandthepossecomitatuswhenthereisonlyacarpettoshakeorarefuse-barreltoempty。[Dr。JamesJohnsonadvisespersonsnotailingtotake，fivegrainsofbluepillwithoneortwoofaloestwiceaweekforthreeorfourmonthsintheyear，withhalfapintofcompounddecoctionofsarsaparillaeverydayforthesameperiod，topreservehealthandprolonglife。Pract。TreatiseonDis。ofLiver，etc。p。272。]Theconstitutionbearsslowpoisoningagreatdealbetterthanmightbeexpected；yetthemostintelligentmenintheprofessionhavegraduallygotoutofthehabitofprescribingthesepowerfulaliensubstancesintheoldroutineway。Mr。Metcalfwilltellyouhowmuchmoresparinglytheyaregivenbyourpractitionersatthepresenttime，thanwhenhefirstinauguratedtheneweraofpharmacyamongus。Still，thepresumptioninfavorofpoisoningouteveryspontaneousreactionofoutragednatureisnotextinctinthosewhoaretrustedwiththelivesoftheirfellow-
　　citizens。“Onexaminingthefileofprescriptionsatthehospital，I
　　discoveredthattheywererudelywritten，andindicatedatreatment，astheyconsistedchieflyoftartaremetic，ipecacuanha，andepsomsalts，hardlyfavorabletothecureoftheprevailingdiarrhoeaanddysenteries。“Inareportofapoisoningcasenowontrial，wherewearetoldthatarsenicenoughwasfoundinthestomachtoproducedeathintwenty-fourhours，thepatientissaidtohavebeentreatedbyarsenic，phosphorus，bryonia，aconite，nuxvomica，andmuriaticacid，——byapractitionerofwhatschoolitmaybeimagined。
　　Thetraditionalideaofalwayspoisoningoutdisease，aswesmokeoutvermin，isnowseekingitslastrefugebehindthewoodencannonandpaintedport-holesofthatunblushingsystemoffalsescientificpretenceswhichIdonotcaretonameinadiscourseaddressedtoanaudiencedevotedtothestudyofthelawsofnatureinthelightofthelawsofevidence。Itisextraordinarytoobservethatthesystemwhich，byitsreducingmedicinetoanameandafarce，hasaccustomedallwhohavesenseenoughtoseethroughitsthinartificestotheideathatdiseasesgetwellwithoutbeing“cured，“shouldnowbethemainsupportofthetotteringpoison-curedoctrine。Ithasunquestionablyhelpedtoteachwisepeoplethatnaturehealsmostdiseaseswithouthelpfrompharmaceuticart，butitcontinuestopersuadefoolsthatartcanarrestthemallwithitsspecifics。
　　Itisworsethanuselesstoattemptinanywaytocheckthefreestexpressionofopinionastotheefficacyofanyorallofthe“heroic“meansoftreatmentemployedbypractitionersofdifferentschoolsandperiods。Medicalexperienceisagreatthing，butwemustnotforgetthatthereisahigherexperience，whichtriesitsresultsinacourtofastilllargerjurisdiction；that，namely，inwhichthelawsofhumanbeliefaresummonedtothewitness-box，andobligedtotestifytothesourcesoferrorwhichbesetthemedicalpractitioner。Theverdictisasoldasthefatherofmedicine，whoannouncesitinthewords，“judgmentisdifficult。“Physiciansdifferedsoinhistime，thatsomedeniedthattherewasanysuchthingasanartofmedicine。
　　Oneman’sbestremedieswereheldasmischievousbyanother。Theartofhealingwaslikesoothsaying，sothecommonpeoplesaid；thesamebirdwasluckyorunlucky，accordingasheflewtotherightorleft。“
　　Thepracticeofmedicinehasundergonegreatchangeswithintheperiodofmyownobservation。Venesection，forinstance，hassofargoneoutoffashion，that，asIamtoldbyresidentsoftheNewYorkBellevueandtheMassachusettsGeneralHospitals，itisalmostobsoleteintheseinstitutions，atleastinmedicalpractice。TheoldBrunonianstimulatingtreatmenthascomeintovogueagaininthepracticeofDr。Toddandhisfollowers。Thecompoundsofmercuryhaveyieldedtheirplaceasdrugsofallwork，andspecificsforthatveryfrequentsubjectivecomplaint，nescioquidfaciam，——tocompoundsofiodine。[SirAstleyCooperhastheboldness，——orhonesty，——tospeakofmedicineswhich“aregivenasmuchtoassistthemedicalmanashispatient。“LecturesLondon，1832，p。14。]Opiumisbelievedin，andquinine，and“rum，“usingthatexpressivemonosyllabletomeanallalcoholiccordials。IfMolierewerewritingnow，insteadofsaignare，purgare，andtheother，hewouldbemoreliketosay，Stimulare，opiumdareetpotassio-iodizare。
　　IhavebeeninrelationsuccessivelywiththeEnglishandAmericanevacuantandalterativepractice，inwhichcalomelandantimonyfiguredsolargelythat，asyoumayseeinDr。Jackson’slast“Letter，“Dr。Holyoke，agoodrepresentativeofsterlingold-
　　fashionedmedicalart，countedthemwithopiumandPeruvianbarkashischiefremedies；withthemoderatelyexpectantpracticeofLouis；
　　theblood-letting“coupsurcoup“ofBouillaud；thecontra-stimulantmethodofRasoriandhisfollowers；theanti-irritantsystemofBroussais，withitsleechingandgum-water；IhaveheardfromourownstudentsofthesimpleopiumpracticeoftherenownedGermanteacher，Oppolzer；andnowIfindthemedicalcommunitybroughtroundbytherevolvingcycleofopiniontothatsameoldplanoftreatmentwhichJohnBrowntaughtinEdinburghinthelastquarterofthelastcentury，andMinerandTullyfiercelyadvocatedamongourselvesintheearlyyearsofthepresent。Theworthyphysicianslastmentioned，andtheirantagonistDr。Gallup，usedstrongerlanguagethanweofthesedegeneratedayspermitourselves。“Thelancetisaweaponwhichannuallyslaysmorethanthesword，“saysDr。Tully。
　　“Itisprobablethat，forfortyyearspast，opiumanditspreparationshavedoneseventimestheinjurytheyhaverenderedbenefit，onthegreatscaleoftheworld，“saysDr。Gallup。
　　Whatisthemeaningoftheseperpetualchangesandconflictsofmedicalopinionandpractice，fromanearlyantiquitytoourowntime？Simplythis：all“methods“oftreatmentendindisappointmentofthoseextravagantexpectationswhichmenarewonttoentertainofmedicalart。Thebillsofmortalityaremoreobviouslyaffectedbydrainage，thanbythisorthatmethodofpractice。Theinsurancecompaniesdonotcommonlychargeadifferentpercentageonthelivesofthepatientsofthisorthatphysician。Inthecourseofageneration，moreorless，physiciansthemselvesareliabletogettiredofapracticewhichhassolittleeffectupontheaveragemovementofvitaldecomposition。Thentheyarereadyforachange，evenifitwerebackagaintoamethodwhichhasalreadybeentried，andfoundwanting。
　　Ourpractitioners，ormanyofthem，havegotbacktothewaysofoldDr。SamuelDanforth，who，asitiswellknown，hadstrongobjectionstotheuseofthelancet。Byandbyanewreputationwillbemadebysomediscontentedpractitioner，who，tiredofseeingpatientsdiewiththeirskinsfullofwhiskeyandtheirbrainsmuddywithopium，returnstoaboldantiphlogistictreatment，andhasthelucktoseeafewpatientsofnotegetwellunderit。Sooftheremedieswhichhavegoneoutoffashionandbeensupersededbyothers。Itcanhardlybedoubtedthattheywillcomeintovogueagain，moreorlessextensively，undertheinfluenceofthatirresistibledemandforchangejustreferredto。
　　Thenwillcometheusualtalkaboutachangeinthecharacterofdisease，whichhasaboutasmuchmeaningasthatconcerning“old-fashionedsnow-storms。““Epidemicconstitutions“ofdiseasemeansomething，nodoubt；agreatdealasappliedtomalariousaffections；butthatthewholetypeofdiseasesundergoessuchchangesthatthepracticemustbereversedfromdepletingtostimulating，andviceversa，ismuchlesslikelythanthatmethodsoftreatmentgooutoffashionandcomeinagain。Ifthereisanydiseasewhichclaimsitspercentagewithreasonableuniformity，itisphthisis。YetIrememberthatthereverendandvenerableDr。PrinceofSalemtoldmeoneCommencementday，asIwasjoggingalongtowardsCambridgewithhim，thatherecollectedthetimewhenthatdiseasewashardlyhardlyknown；andinconfirmationofhisstatementmentionedacaseinwhichitwastoldasagreatevent，thatsomebodydownon“theCape“haddiedof“aconsumption。“Thisstorydoesnotsoundprobabletomyself，asIrepeatit，yetIassureyouitistrue，anditshowshowcautiouslywemustreceiveallpopularstoriesofgreatchangesinthehabitsofdisease。