Whilethesestudiesofthestructureofthecordhavebeengoingon，theingeniousandindefatigableBrown-Sequardhasbeeninvestigatingthefunctionsofitsdifferentpartswithequaldiligence。Themicroscopicanatomistshadshownthattheganglioniccorpusclesofthegraymatterofthecordareconnectedwitheachotherbytheirprocesses，aswellaswiththenerve-roots。M。Brown-Sequardhasprovedbynumerousexperimentsthatthegraysubstancetransmitssensitiveimpressionsandmuscularstimulation。Theobliqueascendinganddescendingfibresfromtheposteriornerve-roots，joiningthe“longitudinalcolumnsofthecornua，“accountfortheresultsofBrown-Sequard’ssectionsoftheposteriorcolumns。Thephysiologicalexperimenterhasalsomadeitevidentthatthedecussationoftheconductorsofsensitiveimpressionshasitsseatinthespinalcore，andnotintheencephalon，ashadbeensupposed。
Notlessremarkablethantheseresultsarethefacts，whichIwithothersofmyaudiencehavehadtheopportunityofobserving，asshownbyM。Brown-S6quard，oftheartificialproductionofepilepsyinanimalsbyinjuringthespinalcord，andtheinductionoftheparoxysmbypinchingacertainportionoftheskin。Iwouldalsocallthestudent’sattentiontohisaccountoftherelationsofthenervouscentrestonutritionandsecretion，thelastofwhichrelationshasbeenmadethesubjectofanextendedessaybyourfellowcountryman，Dr。H。F。CampbellofGeorgia。
ThephysiologyofthespinalcordseemsasimplematterasyoustudyitinLonget。TheexperimentsofBrown-Sequardhaveshowntheproblemtobeacomplexone，andraisedalmostasmanydoubtsastheyhavesolvedquestions；atanyrate，Ibelievealllecturersonphysiologyagreethatthereisnopartoftheirtasktheydreadsomuchastheanalysisoftheevidencerelatingtothespecialofficesofthedifferentportionsofthemedullaspinalis。Inthebrainwearesurethatwedonotknowhowtolocalizefunctions；inthespinalcord，wethinkwedoknowsomething；buttherearesomanyanomalies，andseemingcontradictions，andsourcesoffallacy，thatbeyondthefactsofcrossedparalysisofsensation，andtheconductingagencyofthegraysubstance，IamafraidweretainnocardinalprinciplesdiscoveredsincethedevelopmentofthereflexfunctiontookitsplacebySirCharlesBell’sgreatdiscovery。
BythemannerinwhichIspokeofthebrain，youwillseethatIamobligedtoleavephrenologysubJove，——outinthecold，——asnotoneofthehouseholdofscience。Iamnotoneofitshaters；onthecontrary，Iamgratefulfortheincidentalgoodithasdone。IlovetoamusemyselfinitsplasterGolgothas，andlistentotheglibprofessor，ashediscoversbyhismanipulations“Allthatdisgracedmybettersmetinme。“
Ilovedofoldtoseesquare-headed，heavy-jawedSpurzheimmakeabrainfloweroutintoacorollaofmarrowyfilaments，asVieussenshaddonebeforehim，andtohearthedry-fibredbuthuman-heartedGeorgeCombeteachgoodsenseunderthedisguiseofhisequivocalsystem。Butthepseudo-sciences，phrenologyandtherest，seemtomeonlyappealstoweakmindsandtheweakpointsofstrongones。Thereisapicaorfalseappetiteinmanyintelligences；theytaketooddfanciesinplaceofwholesometruth，asgirlsgnawatchalkandcharcoal。Phrenologyjuggleswithnature。Itissoadjustedastosoakupallevidencethathelpsit，andshedallthatharmsit。Itcrawlsforwardinallweathers，likeRichardEdgeworth’shygrometer。
Itdoesnotstandattheboundaryofourignorance，itseemstome，butisoneofthewill-o’-the-wispsofitsundisputedcentraldomainofbogandquicksand。YetIshouldnothavedevotedsomanywordstoit，didInotrecognizethelightithasthrownonhumanactionsbyitsstudyofcongenitalorganictendencies。Itsmapsofthe。
surfaceoftheheadare，Ifeelsure，foundedonadelusion，butitsstudiesofindividualcharacterarealwaysinterestingandinstructive。
The“snapping-turtle“strikesafteritsnaturalfashionwhenitfirstcomesoutoftheegg。Childrenbetraytheirtendenciesintheirwayofdealingwiththebreaststhatnourishthem；nay，leanventuretoaffirm，thatlongbeforetheyareborntheyteachtheirmotherssomethingoftheirturbulentorquiettempers。
“Castorgaudetequis，ovoproanatuseodemPugnis。“
Strikeoutthefalsepretensionsofphrenology；callitanthropology；
letitstudymantheindividualindistinctionfrommantheabstraction，themetaphysicalortheologicallay-figure；anditbecomes“theproperstudyofmankind，“oneofthenoblestandmostinterestingofpursuits。
Thewholephysiologyofthenervoussystem，fromthesimplestmanifestationofitspowerinaninsectuptothesupremeactofthehumanintelligenceworkingthroughthebrain，isfullofthemostdifficultyetprofoundlyinterestingquestions。Thesingularrelationsbetweenelectricityandnerve-force，relationswhichithasbeenattemptedtointerpretasmeaningidentity，inthefaceofpalpabledifferences，requirestillmoreextendedstudies。YoumaybeinterestedbyProfessorFaraday’sstatementofhisopiniononthematter。“ThoughIamnotsatisfiedthatthenervousfluidisonlyelectricity，stillIthinkthattheagentinthenervoussystemmaybeaninorganicforce；andiftherebereasonforsupposingthatmagnetismisahigherrelationofforcethanelectricity，soitmaywellbeimaginedthatthenervouspowermaybeofastillmoreexaltedcharacter，andyetwithinthereachofexperiment。“
Inconnectionwiththisstatement，itisinterestingtorefertotheexperimentsofHelmholtzontherapidityoftransmissionofthenervousactions。TherateisgivendifferentlyinValentin’sreportoftheseexperimentsandinthatfoundinthe“ScientificAnnual“for1858。Onehundredandeightytothreehundredfeetpersecondistherateofmovementassignedforsensation，butallsuchresultsmustbeveryvaguelyapproximative。Boxers，fencers，playersattheItaliangameofmorn，“prestidigitators，“andallwhodependfortheirsuccessonrapidityofmotion，knowwhatdifferencesthereareinthepersonalequationofmovement。
Reflexaction，themechanicalsympathy，ifImaysocallit，ofdistantparts；Instinct，whichiscrystallizedintelligence，——anabsolutelawwithitsinvariableplanesandanglesintroducedintothesphereofconsciousness，asraphidesareinclosedinthelivingcellsofplants；Intellect，——theoperationofthethinkingprinciplethroughmaterialorgans，withanappreciablewasteoftissueineveryactofthought，sothatourclergymen’sbloodhasmorephosphatestogetridofonMondaythanonanyotherdayoftheweek；Will，——
theoreticallytheabsolutedeterminingpower，practicallylimitedindifferentdegreesbythevaryingorganizationofracesandindividuals，annulledorpervertedbydifferentill-understoodorganicchanges；onallthesesubjectsourknowledgeisinitsinfancy，andfromthestudyofsomeofthemtheinterdictoftheVaticanishardlyyetremoved。
Imustalludetooneortwopointsinthehistologyandphysiologyoftheorgansofsense。Theanteriorcontinuationoftheretinabeyondtheoraserratahasbeenasubjectofmuchdiscussion。IfH。MullerandKollikercanbereliedupon，thisquestionissettledbyrecognizingthatalayerofcells，continuedfromtheretina，passesoverthesurfaceofthezonulaZinnii，butthatnopropernervouselementissoprolongedforward。
IobservethatKollikercallsthetruenervouselementsoftheretina“thelayerofgraycerebralsubstance。“Infact，theganglioniccorpusclesofeacheyemaybeconsideredasconstitutingalittlebrain，connectedwiththemassesbehindbythecommissure，commonlycalledtheopticnerve。Weareprepared，therefore，tofindthesetwolittlebrainsinthemostintimaterelationswitheachother，aswefindthecerebralhemispheres。Weknowthattheyaredirectlyconnectedbyfibresthatarchroundthroughthechiasma。
Imentiontheseanatomicalfactstointroduceaphysiologicalobservationofmyown，firstannouncedinoneofthelecturesbeforetheMedicalClass，subsequentlycommunicatedtotheAmericanAcademyofArtsandSciences，andprintedinits“Transactions“forFebruary14，1860。Irefertotheapparenttransferofimpressionsfromoneretinatotheother，towhichIhavegiventhenamereflexvision。
Theideawassuggestedtomeinconsequenceofcertaineffectsnoticedinemployingthestereoscope。ProfessorWilliamB。RodgershassincecalledtheattentionoftheAmericanScientificAssociationtosomefactsbearingonthesubject，andtoaverycuriousexperimentofLeonardodaVinci’s，whichenablestheobservertolookthroughthepalmofhishandorseemto，asifithadaholeboredthroughit。Asheandothershesitatedtoacceptmyexplanation，I
wasnotsorrytofindrecentlythefollowingwordsinthe“ObservationsonMan“ofthatacuteobserverandthinker，DavidHartley。“Animpressionmadeontherighteyealonebyasingleobjectmaypropagateitselfintotheleft，andthereraiseupanimagealmostequalinvividnesstoitself；andconsequentlywhenweseewithoneeyeonly，wemay，however，havepicturesinbotheyes。“
Hartley，in1784，hadanticipatedmanyofthedoctrineswhichhavesincebeensystematizedintothetheoryofreflexactions，andwithwhichIhaveattemptedtoassociatethisactofreflexvision。Mysixthexperiment，however，inthecommunicationreferredto，appearstometobeacrucialone，provingthecorrectnessofmyexplanation，andIamnotawarethatithasbeenbeforeinstituted。
Anotherpointofgreatinterestconnectedwiththephysiologyofvision，andinvolvedforalongtimeingreatobscurity，isthatoftheadjustmentoftheeyetodifferentdistances。Dr。ClayWallaceofNewYork，whopublishedaveryingeniouslittlebookontheeyeabouttwentyyearsago，withvignettesremindingoneofBewick，wasamongthefirst，ifnotthefirst，todescribetheciliarymuscle，towhichthepowerofadjustmentisgenerallyascribed。Itisascertained，byexactexperimentwiththephacueidoscope，thataccommodationdependsonchangeofformofthecrystallinelens。
Wherethecrystallineiswanting，asMr。Warelongagotaught，nopowerofaccommodationremains。Theciliarymuscleisgenerallythoughttoeffectthechangeofformofthecrystalline。Thepowerofaccommodationislostaftertheapplicationofatropine，inconsequence，asissupposed，oftheparalysisofthismuscle。This，Ibelieve，isthenearestapproachtoademonstrationwehaveonthispoint。
IhaveonlytimebrieflytorefertoProfessorDraper’smostingenioustheoryastothephotographicnatureofvision，foranaccountofwhichImustrefertohisoriginalandinterestingTreatiseonPhysiology。
ItweretobewishedthattheelaborateandveryinterestingresearchesoftheMarquisCorti，whichhaverevealedsuchsingularcomplexityofstructureinthecochleaoftheear，haddonemoretoclearupitsdoubtfulphysiology；butIamafraidwehavenothingbuthypothesesforthespecialpartitplaysintheactofhearing，andthatwemustsaythesamerespectingtheofficeofthesemicircularcanals。
Themicroscopehasachievedsomeofitsgreatesttriumphsinteachingusthechangeswhichoccurinthedevelopmentoftheembryo。NomoreinterestingdiscoverystandsrecordedinthevoluminousliteratureofthissubjectthantheoneoriginallyannouncedbyMartinBarry，afterwardsdiscredited，andstilllaterconfirmedbyMr。Newportandothers；namelythefactthatthefertilizingfilamentreachestheinterioroftheovuminvariousanimals；——astrikingparalleltotheactionofthepollen-tubeinthevegetable。Butbeyondthemechanicalfactsallismysteryinthemovementsoforganization，asprofoundasinthefallofastoneortheformationofacrystal。
Tothechemistandthemicroscopistthelivingbodypresentsthesamedifficulties，arisingfromthefactthateverythingisinperpetualchangeintheorganism。Thefibrineofthebloodpuzzlestheoneasmuchasitsglobulespuzzletheother。Thedifferencebetweenthebranchesofsciencewhichdealwithspaceonly，andthosewhichdealwithspaceandtime，isthis：wehavenoglassesthatcanmagnifytime。ThefigureIhereshowyouawasphotographedfromanobjectpleurosigmaangulatummagnifiedathousanddiameters，orpresentingamilliontimesitsnaturalsurface。Thisotherfigureofthesameobject，enlargedfromtheonejustshown，ismagnifiedseventhousanddiameters，orforty-ninemilliontimesinsurface。Whenwecanmaketheforty-ninemillionthofasecondaslongasitsinteger，physiologyandchemistrywillapproachnearerthecompletenessofanatomy。
Ourreverencebecomesmoreworthy，or，ifyouwill，lessunworthyofitsInfiniteObjectinproportionasourintelligenceisliftedandexpandedtoahigherandbroaderunderstandingoftheDivinemethodsofaction。IfGalencalledhisheathenreaderstoadmire，thepower，thewisdom，theprovidence，thegoodnessoftheFrameroftheanimalbody，“——ifMr。Boyle，thestudentofnature，asAddisonandthatfriendofhiswhohadknownhimforfortyyearstellus，neverutteredthenameoftheSupremeBeingwithoutmakingadistinctpauseinhisspeech，intokenofhisdevoutrecognitionofitsawfulmeaning，——surelywe，whoinherittheaccumulatedwisdomofnearlytwohundredyearssincethetimeoftheBritishphilosopher，andofalmosttwothousandsincetheGreekphysician，maywellliftourthoughtsfromtheworkswestudytotheirgreatArtificer。Thesewonderfuldiscoverieswhichweowetothatmightylittleinstrument，thetelescopeoftheinnerfirmamentwithallitsincludedworlds；