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Theyrisebeforeme，thedeadandtheliving，inthemidstofthemostgratefulrecollections。Thefair，manlyfaceandstatelyfigureofmyfriend，Dr。SamuelParkman，himselffitforthehighestofficesofteaching，yetwillingtobemyfaithfulassistantinthetimeofneed，comebacktomewiththelongsighofregretforhisearlylosstoourearthlycompanionship。EveryyearIspeaktheeulogyofDr。
Ainsworth’spatienttoilasIshowhiselaboratepreparations：WhenI
takedownmy“AmericanCyclopaedia“andborrowinstructionfromthelearnedarticlesofDr。Kneeland，Iceasetoregretthathisindefatigableandintelligentindustrywasturnedintoabroaderchannel。AndwhatcanIsaytoocordialofmylongassociatedcompanionandfriend，Dr。Hodges，whoseadmirableskill，workingthroughtheswiftestandsurestfingersthateverheldascalpelamongus，hasdelightedclassafterclass，andfilledourMuseumwithmonumentswhichwillconveyhisnametounborngenerations？
Thisdaybelongs，however，nottomyselfandmyrecollections，buttoallofuswhoteachandallofyouwholisten，whetherexpertsinourspecialtiesoralienstotheirmysteries，ortimidneophytesjustenteringtheportalsofthehallofscience。Lookinwithme，then，whileIattempttothrowsomeraysintoitsinterior，whichshallilluminateafewofitspillarsandcornices，andshowatthesametimehowmanynichesandalcovesremainindarkness。
SCIENCEisthetopographyofignorance。Fromafewelevatedpointswetriangulatevastspaces，inclosinginfiniteunknowndetails。Wecastthelead，anddrawupalittlesandfromabysseswemayneverreachwithourdredges。
Thebestpartofourknowledgeisthatwhichteachesuswhereknowledgeleavesoffandignorancebegins。Nothingmoreclearlyseparatesavulgarfromasuperiormind，thantheconfusioninthefirstbetweenthelittlethatittrulyknows，ontheonehand，andwhatithalfknowsandwhatitthinksitknowsontheother。
Thatwhichistrueofeverysubjectisespeciallytrueofthebranchofknowledgewhichdealswithlivingbeings。Theirexistenceisaperpetualdeathandreanimation。Theiridentityisonlyanidea，forweputoffourbodiesmanytimesduringourlives，anddressinnewsuitsofbonesandmuscles。
“Thouartnotthyself；
Forthouexist’stonmanyathousandgrainsThatissueoutofdust。“
Ifitistruethatweunderstandourselvesbutimperfectlyinhealth，thistruthismoresignallymanifestedindisease，wherenaturalactionsimperfectlyunderstood，disturbedinanobscurewaybyhalf-
seencauses，arecreepingandwindingalonginthedarktowardtheirdestinedissue，sometimesusingourremediesassafestepping-stones，occasionally，itmaybe，stumblingoverthemasobstacles。
Iproposeinthislecturetoshowyousomepointsofcontactbetweenourignoranceandourknowledgeinseveralofthebranchesuponthestudyofwhichyouareentering。Imayteachyouaverylittledirectly，butIhopemuchmorefromthetrainsofthoughtIshallsuggest。Donotexpecttoomuchgroundtobecoveredinthisrapidsurvey。Ourtaskisonlythatofsendingoutafewpicketsunderthestarryflagofsciencetotheedgeofthatdarkdomainwheretheensignsoftheobstinaterebel，Ignorance，areflyingundisputed。Wearenotmakingareconnoissanceinforce，stilllessadvancingwiththemaincolumn。Buthereareafewroadsalongwhichwehavetomarchtogether，andwewishtoseeclearlyhowfarourlinesextend，andwheretheenemy’soutpostsbegin。
Beforetouchingthebranchesofknowledgethatdealwithorganizationandvitalfunctions，letusglanceatthatsciencewhichmeetsyouatthethresholdofyourstudy，andpreparesyouinsomemeasuretodealwiththemorecomplexproblemsofthelivinglaboratory。
CHEMISTRY。includestheartofseparatingandcombiningtheelementsofmatter，andthestudyofthechangesproducedbytheseoperations。
Wecanhardlysaytoomuchofwhatithascontributedtoourknowledgeoftheuniverseandourpowerofdealingwithitsmaterials。Ithasgivenusacatalogueraisonneofthesubstancesfounduponourplanet，andshownhoweverythinglivinganddeadisputtogetherfromthem。Itisaccomplishingwondersbeforeuseveryday，suchasArabianstory-tellersusedtostringtogetherintheirfables。Itspreadsthe，sensitivefilmontheartificialretinawhichlooksuponusthroughtheoptician’slensforafewseconds，andfixesanimagethatwilloutliveitsoriginal。Itquestion
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