p　to　the　supreme　act　of　the　human　intelligence　working　through　the　brain；　is　full　of　the　most　difficult　yet　profoundly　interesting　questions。　　The　singular　relations　between　electricity　and　nerve…force；　relations　which　it　has　been　attempted　to　interpret　as　meaning　identity；　in　the　face　of　palpable　differences；　require　still　more　extended　studies。　　You　may　be　interested　by　Professor　Faraday's　statement　of　his　opinion　on　the　matter。　　〃Though　I　am　not　satisfied　that　the　nervous　fluid　is　only　electricity；　still　I　think　that　the　agent　in　the　nervous　system　maybe　an　inorganic　force；　and　if　there　be　reason　for　supposing　that　magnetism　is　a　higher　relation　of　force　than　electricity；　so　it　may　well　be　imagined　that　the　nervous　power　may　be　of　a　still　more　exalted　character；　and　yet　within　the　reach　of　experiment。〃
  In　connection　with　this　statement；　it　is　interesting　to　refer　to　the　experiments　of　Helmholtz　on　the　rapidity　of　transmission　of　the　nervous　actions。　　The　rate　is　given　differently　in　Valentin's　report　of　these　experiments　and　in　that　found　in　the　〃Scientific　Annual〃　for　1858。　　One　hundred　and　eighty　to　three　hundred　feet　per　second　is　the　rate　of　movement　assigned　for　sensation；　but　all　such　results　must　be　very　vaguely　approximative。　　Boxers；　fencers；　players　at　the　Italian　game　of　morn；　〃prestidigitators；〃　and　all　who　depend　for　their　success　on　rapidity　of　motion；　know　what　differences　there　are　in　the　personal　equation　of　movement。
  Reflex　action；　the　mechanical　sympathy；　if　I　may　so　call　it；　of　distant　parts；　Instinct；　which　is　crystallized　intelligence；an　absolute　law　with　its　invariable　planes　and　angles　introduced　into　the　sphere　of　consciousness；　as　raphides　are　inclosed　in　the　living　cells　of　plants；　Intellect；the　operation　of　the　thinking　principle　through　material　organs；　with　an　appreciable　waste　of　tissue　in　every　act　of　thought；　so　that　our　clergymen's　blood　has　more　phosphates　to　get　rid　of　on　Monday　than　on　any　other　day　of　the　week；　Will；　theoretically　the　absolute　determining　power；　practically　limited　in　different　degrees　by　the　varying　organization　of　races　and　individuals；　annulled　or　perverted　by　different　ill…understood　organic　changes；　on　all　these　subjects　our　knowledge　is　in　its　infancy；　and　from　the　study　of　some　of　them　the　interdict　of　the　Vatican　is　hardly　yet　removed。
  I　must　allude　to　one　or　two　points　in　the　histology　and　physiology　of　the　organs　of　sense。　　The　anterior　continuation　of　the　retina　beyond　the　ora　serrata　has　been　a　subject　of　much　discussion。　　If　H。　Muller　and　Kolliker　can　be　relied　upon；　this　question　is　settled　by　recognizing　that　a　layer　of　cells；　continued　from　the　retina；　passes　over　the　surface　of　the　zonula　Zinnii；　but　that　no　proper　nervous　element　is　so　prolonged　forward。
  I　observe　that　Kolliker　calls　the　true　nervous　elements　of　the　retina　〃the　layer　of　gray　cerebral　substance。〃　　In　fact；　the　ganglionic　corpuscles　of　each　eye　may　be　considered　as　constituting　a　little　brain；　connected　with　the　masses　behind　by　the　commissure；　commonly　called　the　optic　nerve。　　We　are　prepared；　therefore；　to　find　these　two　little　brains　in　the　most　intimate　relations　with　each　other；　as　we　find　the　cerebral　hemispheres。　　We　know　that　they　are　directly　connected　by　fibres　that　arch　round　through　the　chiasma。
  I　mention　these　anatomical　facts　to　introduce　a　physiological　observation　of　my　own；　first　announced　in　one　of　the　lectures　before　the　Medical　Class；　subsequently　communicated　to　the　American　Academy　of　Arts　and　Sciences；　and　printed　in　its　〃Transactions〃　for　February　14；　1860。　　I　refer　to　the　apparent　transfer　of　impressions　from　one　retina　to　the　other；　to　which　I　have　given　the　name　reflex　vision。　The　idea　was　suggested　to　me　in　consequence　of　certain　effects　noticed　in　employing　the　stereoscope。　　Professor　William　B。　Rodgers　has　since　called　the　attention　of　the　American　Scientific　Association　to　some　facts　bearing　on　the　subject；　and　to　a　very　curious　experiment　of　Leonardo　da　Vinci's；　which　enables　the　observer　to　look　through　the　palm　of　his　hand　（or　seem　to）；　as　if　it　had　a　hole　bored　through　it。　　As　he　and　others　hesitated　to　accept　my　explanation；　I　was　not　sorry　to　find　recently　the　following　words　in　the　〃Observations　on　Man〃　of　that　acute　observer　and　thinker；　David　Hartley。　　〃An　impression　made　on　the　right　eye　alone　by　a　single　object　may　propagate　itself　into　the　left；　and　there　raise　up　an　image　almost　equal　in　vividness　to　itself；　and　consequently　when　we　see　with　one　eye　only；　we　may；　however；　have　pictures　in　both　eyes。〃　Hartley；　in　1784；　had　anticipated　many　of　the　doctrines　which　have　since　been　systematized　into　the　theory　of　reflex　actions；　and　with　which　I　have　attempted　to　associate　this　act　of　reflex　vision。　　My　sixth　experiment；　however；　in　the　communication　referred　to；　appears　to　me　to　be　a　crucial　one；　proving　the　correctness　of　my　explanation；　and　I　am　not　aware　that　it　has　been　before　instituted。
  Another　point　of　great　interest　connected　with　the　physiology　of　vision；　and　involved　for　a　long　time　in　great　obscurity；　is　that　of　the　adjustment　of　the　eye　to　different　distances。　　Dr。　Clay　Wallace　of　New　York；　who　published　a　very　ingenious　little　book　on　the　eye　about　twenty　years　ago；　with　vignettes　reminding　one　of　Bewick；　was　among　the　first；　if　not　the　first；　to　describe　the　ciliary　muscle；　to　which　the　power　of　adjustment　is　generally　ascribed。　　It　is　ascertained；　by　exact　experiment　with　the　phacueidoscope；　that　accommodation　depends　on　change　of　form　of　the　crystalline　lens。　Where　the　crystalline　is　wanting；　as　Mr。　Ware　long　ago　taught；　no　power　of　accommodation　remains。　　The　ciliary　muscle　is　generally　thought　to　effect　the　change　of　form　of　the　crystalline。　　The　power　of　accommodation　is　lost　after　the　application　of　atropine；　in　consequence；　as　is　supposed；　of　the　paralysis　of　this　muscle。　　This；　I　believe；　is　the　nearest　approach　to　a　demonstration　we　have　on　this　point。
  I　have　only　time　briefly　to　refer　to　Professor　Draper's　most　ingenious　theory　as　to　the　photographic　nature　of　vision；　for　an　account　of　which　I　must　refer　to　his　original　and　interesting　Treatise　on　Physiology。
  It　were　to　be　wished　that　the　elaborate　and　very　interesting　researches　of　the　Marquis　Corti；　which　have　revealed　such　singular　complexity　of　structure　in　the　cochlea　of　the　ear；　had　done　more　to　clear　up　its　doubtful　physiology；　but　I　am　afraid　we　have　nothing　but　hypotheses　for　the　special　part　it　plays　in　the　act　of　hearing；　and　that　we　must　say　the　same　respecting　the　office　of　the　semicircular　canals。
  The　microscope　has　achieved　some　of　its　greatest　triumphs　in　teaching　us　the　changes　which　occur　in　the　development　of　the　embryo。　　No　more　interesting　discovery　stands　recorded　in　the　voluminous　literature　of　this　subject　than　the　one　originally　announced　by　Martin　Barry；　afterwards　discredited；　and　still　later　confirmed　by　Mr。　Newport　and　others；　namely　the　fact　that　the　fertilizing　filament　reaches　the　interior　of　the　ovum　in　various　animals；a　striking　parallel　to　the　action　of　the　pollen…tube　in　the　vegetable。　　But　beyond　the　mechanical　facts　all　is　mystery　in　the　movements　of　organization；　as　profound　as　in　the　fall　of　a　stone　or　the　formation　of　a　crystal。
  To　the　chemist　and　the　microscopist　the　living　body　presents　the　same　difficulties；　arising　from　the　fact　that　everything　is　in　perpetual　change　in　the　organism。　　The　fibrine　of　the　blood　puzzles　the　one　as　much　as　its　globules　puzzle　the　other。　　The　difference　between　the　branches　of　science　which　deal　with　space　only；　and　those　which　deal　with　space　and　time；　is　this：　we　have　no　glasses　that　can　magnify　time。　　The　figure　I　here　show　you　a　was　photographed　from　an　object　（pleurosigma　angulatum）　magnified　a　thousand　diameters；　or　presenting　a　million　times　its　natural　surface。　　This　other　figure　of　the　same　object；　enlarged　from　the　one　just　shown；　is　magnified　seven　thousand　diameters；　or　forty…nine　million　times　in　surface。　　When　we　can　make　the　forty…nine　millionth　of　a　second　as　long　as　its　integer；　physiology　and　chemistry　will　approach　nearer　the　completeness　of　anatomy。
  Our　reverence　becomes　more　worthy；　or；　if　you　will；　less　unworthy　of　its　Infinite　Object　in　proportion　as　our　intelligence　is　lifted　and　expanded　to　a　higher　and　broader　understanding　of　the　Divine　methods　of　action。　　If　Galen　called　his　heathen　readers　to　admire；　the　power；　the　wisdom；　the　providence；　the　goodness　of　the　Framer　of　the　animal　body；〃if　Mr。　Boyle；　the　student　of　nature；　as　Addison　and　that　friend　of　his　who　had　known　him　for　forty　years　tell　us；　never　uttered　the　name　of　the　Supreme　Being　without　making　a　distinct　pause　in　his　speech；　in　token　of　his　devout　recognition　of　its　awful　meaning；surely　we；　who　inherit　the　accumulated　wisdom　of　nearly　two　hundred　years　since　the　time　of　the　British　philosopher；　and　of　almost　two　thousand　since　the　Greek　physician；　may　well　lift　our　thoughts　from　the　works　we　study　to　their　great　Artificer。　　These　wonderful　discoveries　which　we　owe　to　that　mighty　little　instrument；　the　telescope　of　the　inner　firmament　with　all　its　included　worlds；　these　simple　formulae　by　which　we　condense　the　observations　of　a　generation　in　a　single　axiom；　these　logical　analyses　by　which　we　f