ng　their　intersection。　　By　this　their　doctors　are　guided　in　the　performance　of　acupuncture；　marking　the　safe　places　to　thrust　in　needles；　as　we　buoy　out　our　ship…channels；　and　doubtless　indicating　to　learned　eyes　the　spots　where　incautious　meddling　had　led　to　those　little　accidents　of　shipwreck　to　which　patients　are　unfortunately　liable。
  A　change　of　method；　then；　has　given　us　General　and　Regional　Anatomy。　These；　too；　have　been　worked　so　thoroughly；　that；　if　not　exhausted；　they　have　at　least　become　to　a　great　extent　fixed　and　positive　branches　of　knowledge。　　But　the　first　of　them；　General　Anatomy；　would　never；　have　reached　this　positive　condition　but　for　the　introduction　of　that；　instrument　which　I　have　mentioned　as　the　second　great　aid　to　modern　progress。
  This　instrument　is　the　achromatic　microscope。　　For　the　history　of　the　successive　steps　by　which　it　became　the　effective　scientific　implement　we　now　possess；　I　must　refer　you　to　the　work　of　Mr。　Quekett；　to　an　excellent　article　in　the　〃Penny　Cyclopaedia；〃　or　to　that　of　Sir　David　Brewster　in　the　〃Encyclopaedia　Britannica。〃　　It　is　a　most　interesting　piece　of　scientific　history；　which　shows　how　the　problem　which　Biot　in　1821　pronounced　insolvable　was　in　the　course　of　a　few　years　practically　solved；　with　a　success　equal　to　that　which　Dollond　had　long　before　obtained　with　the　telescope。　　It　is　enough　for　our　purpose　that　we　are　now　in　possession　of　an　instrument　freed　from　all　confusions　and　illusions；　which　magnifies　a　thousand　diameters；a　million　times　in　surface；without　serious　distortion　or　discoloration　of　its　object。
  A　quarter　of　a　century　ago；　or　a　little　more；　an　instructor　would　not　have　hesitated　to　put　John　Bell's　〃Anatomy〃　and　Bostock's　〃Physiology〃　into　a　student's　hands；　as　good　authority　on　their　respective　subjects。　　Let　us　not　be　unjust　to　either　of　these　authors。　　John　Bell　is　the　liveliest　medical　writer　that　I　can　remember　who　has　written　since　the　days　of　delightful　old　Ambroise　Pare。　　His　picturesque　descriptions　and　bold　figures　are　as　good　now　as　they　ever　were；　and　his　book　can　never　become　obsolete。　　But　listen　to　what　John　Bell　says　of　the　microscope　：
  〃Philosophers　of　the　last　age　had　been　at　infinite　pains　to　find　the　ultimate　fibre　of　muscles；　thinking　to　discover　its　properties　in　its　form；　but　they　saw　just　in　proportion　to　the　glasses　which　they　used；　or　to　their　practice　and　skill　in　that　art；　which　is　now　almost　forsaken。〃
  Dr。　Bostock's　work；　neglected　as　it　is；　is　one　which　I　value　very　highly　as　a　really　learned　compilation；　full　of　original　references。　But　Dr。　Bostock　says：　〃Much　as　the　naturalist　has　been　indebted　to　the　microscope；　by　bringing　into　view　many　beings　of　which　he　could　not　otherwise　have　ascertained　the　existence；　the　physiologist　has　not　yet　derived　any　great　benefit　from　the　instrument。〃
  These　are　only　specimens　of　the　manner　in　which　the　microscope　and　its　results　were　generally　regarded　by　the　generation　just　preceding　our　own。
  I　have　referred　you　to　the　proper　authorities　for　the　account　of　those　improvements　which　about　the　year　1830　rendered　the　compound　microscope　an　efficient　and　trustworthy　instrument。　　It　was　now　for　the　first　time　that　a　true　general　anatomy　became　possible。　　As　early　as　1816　Treviranus　had　attempted　to　resolve　the　tissues；　of　which　Bichat　had　admitted　no　less　than　twenty…one；　into　their　simple　microscopic　elements。　　How　could　such　an　attempt　succeed；　Henle　well　asks；　at　a　time　when　the　most　extensively　diffused　of　all　the　tissues；　the　areolar；　was　not　at　all　understood？　　All　that　method　could　do　had　been　accomplished　by　Bichat　and　his　followers。　　It　was　for　the　optician　to　take　the　next　step。　　The　future　of　anatomy　and　physiology；　as　an　enthusiastic　micrologist　of　the　time　said；　was　in　the　hands　of　Messrs。　　Schieck　and　Pistor；　famous　opticians　of　Berlin。
  In　those　earlier　days　of　which　I　am　speaking；　all　the　points　of　minute　anatomy　were　involved　in　obscurity。　　Some　found　globules　everywhere；　some　fibres。　　Students　disputed　whether　the　conjunctiva　extended　over　the　cornea　or　not；　and　worried　themselves　over　Gaultier　de　Claubry's　stratified　layers　of　the　skin；　or　Breschet's　blennogenous　and　chromatogenous　organs。　　The　dartos　was　a　puzzle；　the　central　spinal　canal　a　myth；　the　decidua　clothed　in　fable　as　much　as　the　golden　fleece。　　The　structure　of　bone；　now　so　beautifully　made　out；even　that　of　the　teeth；　in　which　old　Leeuwenhoek；　peeping　with　his　octogenarian　eyes　through　the　minute　lenses　wrought　with　his　own　hands；　had　long　ago　seen　the　〃pipes；〃　as　he　called　them；was　hardly　known　at　all。　　The　minute　structure　of　the　viscera　lay　in　the　mists　of　an　uncertain　microscopic　vision。　　The　intimate　recesses　of　the　animal　system　were　to　the　students　of　anatomy　what　the　anterior　of　Africa　long　was　to　geographers；　and　the　stories　of　microscopic　explorers　were　as　much　sneered　at　as　those　of　Bruce　or　Du　Chailly；　and　with　better　reason。
  Now　what　have　we　come　to　in　our　own　day？　　In　the　first　place；　the　minute　structure　of　all　the　organs　has　been　made　out　in　the　most　satisfactory　way。　　The　special　arrangements　of　the　vessels　and　the　ducts　of　all　the　glands；　of　the　air…tubes　and　vesicles　of　the　lungs；　of　the　parts　which　make　up　the　skin　and　other　membranes；　all　the　details　of　those　complex　parenchymatous　organs　which　had　confounded　investigation　so　long；　have　been　lifted　out　of　the　invisible　into　the　sight　of　all　observers。　　It　is　fair　to　mention　here；　that　we　owe　a　great　deal　to　the　art　of　minute　injection；　by　which　we　are　enabled　to　trace　the　smallest　vessels　in　the　midst　of　the　tissues　where　they　are　distributed。　　This　is　an　old　artifice　of　anatomists。　　The　famous　Ruysch；　who　died　a　hundred　and　thirty　years　ago；　showed　that　each　of　the　viscera　has　its　terminal　vessels　arranged　in　its　own　peculiar　way；　the　same　fact　which　you　may　see　illustrated　in　Gerber's　figures　after　the　minute　injections　of　Berres。　　I　hope　to　show　you　many　specimens　of　this　kind　in　the　microscope；　the　work　of　English　and　American　hands。　　Professor　Agassiz　allows　me　also　to　make　use　of　a　very　rich　collection　of　injected　preparations　sent　him　by　Professor　Hyrtl；　formerly　of　Prague；　now　of　Vienna；　for　the　proper　exhibition　of　which　I　had　a　number　of　microscopes　made　expressly；　by　Mr。　Grunow；　during　the　past　season。　　All　this　illustrates　what　has　been　done　for　the　elucidation　of　the　intimate　details　of　formation　of　the　organs。
  But　the　great　triumph　of　the　microscope　as　applied　to　anatomy　has　been　in　the　resolution　of　the　organs　and　the　tissues　into　their　simple　constituent　anatomical　elements。　　It　has　taken　up　general　anatomy　where　Bichat　left　it。　　He　had　succeeded　in　reducing　the　structural　language　of　nature　to　syllables；　if　you　will　permit　me　to　use　so　bold　an　image。　　The　microscopic　observers　who　have　come　after　him　have　analyzed　these　into　letters；　as　we　may　call　them；the　simple　elements　by　the　combination　of　which　Nature　spells　out　successively　tissues；　which　are　her　syllables；　organs　which　are　her　words；　systems　which　are　her　chapters；　and　so　goes　on　from　the　simple　to　the　complex；　until　she　binds　up　in　one　living　whole　that　wondrous　volume　of　power　and　wisdom　which　we　call　the　human　body。
  The　alphabet　of　the　organization　is　so　short　and　simple；　that　I　will　risk　fatiguing　your　attention　by　repeating　it；　according　to　the　plan　I　have　long　adopted。
  A。　　Cells；　either　floating；　as　in　the　blood；　or　fixed；　like　those　in　the　cancellated　structure　of　bone；　already　referred　to。　　Very　commonly　they　have　undergone　a　change　of　figure；　most　frequently　a　flattening　which　reduces　them　to　scales；　as　in　the　epidermis　and　the　epithelium。
  B。　　Simple；　translucent；　homogeneous　solid；　such　as　is　found　at　the　back　of　the　cornea；　or　forming　the　intercellular　substance　of　cartilage。
  C。　　The　white　fibrous　element；　consisting　of　very　delicate；　tenacious　threads。　　This　is　the　long　staple　textile　substance　of　the　body。　　It　is　to　the　organism　what　cotton　is　pretended　to　be　to　our　Southern　States。　　It　pervades　the　whole　animal　fabric　as　areolar　tissue；　which　is　the　universal　packing　and　wrapping　material。　　It　forms　the　ligaments　which　bind　the　whole　frame…work　together。　　It　furnishes　the　sinews；　which　are　the　channels　of　power。　　It　enfolds　every　muscle。　It　wraps　the　brain　in　its　hard；　insensible　folds；　and　the　heart　itself　beats　in　a　purse　that　is　made　of　it。
  D。　　The　yellow　elastic；　fibrous　element；　the　caoutchouc　of　the　animal　mechanism；　which　pulls　things　back　into　place；　as　the　India…rubber　band　shuts　the　door　we　have　opened。
  E。　　The　striped　muscular　fibre；the　red　flesh；　which　shortens　itself　in　obedience　to　the　will；　and　thus　produces　all　voluntary　active　motion。
  F。　　The　unstriped　muscular　fibre；　more　properly　the　fusiform…cell　fibre；　which　carries　on　the　involuntary　internal　movements。
  G。　　The　nerve…cylinder；　a　glassy　tube；　with　a　pith　of　some　firmness；　which　conveys　sensation　to　the　brain　and　the　principle　which　induces　motion　from　it。
  H。　　The　nerve…corpuscle；　the　centre　of　nervous　power。
  I。　　The　mucous　tissue；　as　Virchow　calls　it；　common　in　embryonic　structures；　seen　in　the　vitreous　humor　of　the　adult。
  To　these　add　X；　granules；　of　indeterminate　shape　and　size；　Y；　for　inorganic　matters；　such　as　the　salts　of　bone　and　t