ness　or　joy。　Dr。　Crichton　Browne；　to　whom；　as　on　so　many　other　occasions；　I　am　indebted　for　the　results　of　his　wide　experience；　informs　me　that　with　idiots　laughter　is　the　most　prevalent　and　frequent　of　all　the　emotional　expressions。　Many　idiots　are　morose；　passionate；　restless；　in　a　painful　state　of　mind；　or　utterly　stolid；　and　these　never　laugh。　Others　frequently　laugh　in　a　quite　senseless　manner。　Thus　an　idiot　boy；　incapable　of　speech；　complained　to　Dr。　Browne；　by　the　aid　of　signs；　that　another　boy　in　the　asylum　had　given　him　a　black　eye；　and　this　was　accompanied　by　〃explosions　of　laughter　and　with　his　face　covered　with　the　broadest　smiles。〃　There　is　another　large　class　of　idiots　who　are　persistently　joyous　and　benign；　and　who　are　constantly　laughing　or　smiling。＇3＇　Their　countenances　often　exhibit　a　stereotyped　smile；　their　joyousness　is　increased；　and　they　grin；　chuckle；　or　giggle；　whenever　food　is　placed　before　them；　or　when　they　are　caressed；　are　shown　bright　colours；　or　hear　music。　　Some　of　them　laugh　more　than　usual　when　they　walk　about；　or　attempt　any　muscular　exertion。　The　joyousness　of　most　of　these　idiots　cannot　possibly　be　associated；　as　Dr。　Browne　remarks；　with　any　distinct　ideas：　they　simply　feel　pleasure；　and　express　it　by　laughter　or　smiles。　With　imbeciles　rather　higher　in　the　scale；　personal　vanity　seems　to　be　the　commonest　cause　of　laughter；　and　next　to　this；　pleasure　arising　from　the　approbation　of　their　conduct。
  ＇2＇　F。　Lieber　on　the　vocal　sounds　of　L。　Bridgman；　‘Smithsonian　Contributions；'　1851；　vol。　　ii。　　p。　　6。
  ＇3＇　See；　also；　Mr。　Marshall；　in　Phil。　　Transact。　　1864；　p。　　526。
  With　grown…up　persons　laughter　is　excited　by　causes　considerably　different　from　those　which　suffice　during　childhood；　but　this　remark　hardly　applies　to　smiling。　　Laughter　in　this　respect　is　analogous　with　weeping；　which　with　adults　is　almost　confined　to　mental　distress；　whilst　with　children　it　is　excited　by　bodily　pain　or　any　suffering；　as　well　as　by　fear　or　rage。　　Many　curious　discussions　have　been　written　on　the　causes　of　laughter　with　grown…up　persons。　The　subject　is　extremely　complex。　　Something　incongruous　or　unaccountable；　exciting　surprise　and　some　sense　of　superiority　in　the　laugher；　who　must　be　in　a　happy　frame　of　mind；　seems　to　be　the　commonest　cause。＇4＇　The　circumstances　must　not　be　of　a　momentous　nature：　no　poor　man　would　laugh　or　smile　on　suddenly　hearing　that　a　large　fortune　had　been　bequeathed　to　him。　　If　the　mind　is　strongly　excited　by　pleasurable　feelings；　and　any　little　unexpected　event　or　thought　occurs；　then；　as　Mr。　Herbert　Spencer　remarks；＇5＇　〃a　large　amount　of　nervous　energy；　instead　of　being　allowed　to　expend　itself　in　producing　an　equivalent　amount　of　the　new　thoughts　and　emotion　which　were　nascent；　is　suddenly　checked　in　its　flow。〃　。　。　。　〃The　excess　must　discharge　itself　in　some　other　direction；　and　there　results　an　efflux　through　the　motor　nerves　to　various　classes　of　the　muscles；　producing　the　half…convulsive　actions　we　term　laughter。〃　An　observation；　bearing　on　this　point；　was　made　by　a　correspondent　during　the　recent　siege　of　Paris；　namely；　that　the　German　soldiers。　after　strong　excitement　from　exposure　to　extreme　danger；　were　particularly　apt　to　burst　out　into　loud　laughter　at　the　smallest　joke。　So　again　when　young　children　are　just　beginning　to　cry；　an　unexpected　event　will　sometimes　suddenly　turn　their　crying　into　laughter；　which　apparently　serves　equally　well　to　expend　their　superfluous　nervous　energy。
  ＇4＇　Mr。　Bain　（‘The　Emotions　and　the　Will；'　1865；　p。　　247）　has　a　long　and　interesting　discussion　on　the　Ludicrous。　　The　quotation　above　given　about　the　laughter　of　the　gods　is　taken　from　this　work。　See；　also；　Mandeville；　‘The　Fable　of　the　Bees；'　vol。　　ii。　　p。　　168。
  ＇5＇　‘The　Physiology　of　Laughter；'　Essays；　Second　Series；　1863；　p。　　114。
  The　imagination　is　sometimes　said　to　be　tickled　by　a　ludicrous　idea；　and　this　so…called　tickling　of　the　mind　is　curiously　analogous　with　that　of　the　body。　　Every　one　knows　how　immoderately　children　laugh；　and　how　their　whole　bodies　are　convulsed　when　they　are　tickled。　The　anthropoid　apes；　as　we　have　seen；　likewise　utter　a　reiterated　sound；　corresponding　with　our　laughter；　when　they　are　tickled；　especially　under　the　armpits。　　I　touched　with　a　bit　of　paper　the　sole　of　the　foot　of　one　of　my　infants；　when　only　seven　days　old；　and　it　was　suddenly　jerked　away　and　the　toes　curled　about；　as　in　an　older　child。　　Such　movements；　as　well　as　laughter　from　being　tickled；　are　manifestly　reflex　actions；　and　this　is　likewise　shown　by　the　minute　unstriped　muscles；　which　serve　to　erect　the　separate　hairs　on　the　body；　contracting　near　a　tickled　surface。＇6＇　Yet　laughter　from　a　ludicrous　idea；　though　involuntary；　cannot　be　called　a　strictly　reflex　action。　　In　this　case；　and　in　that　of　laughter　from　being　tickled；　the　mind　must　be　in　a　pleasurable　condition；　a　young　child；　if　tickled　by　a　strange　man；　would　scream　from　fear。　The　touch　must　be　light；　and　an　idea　or　event；　to　be　ludicrous；　must　not　be　of　grave　import。　　The　parts　of　the　body　which　are　most　easily　tickled　are　those　which　are　not　commonly　touched；　such　as　the　armpits　or　between　the　toes；　or　parts　such　as　the　soles　of　the　feet；　which　are　habitually　touched　by　a　broad　surface；　but　the　surface　on　which　we　sit　offers　a　marked　exception　to　this　rule。　　According　to　Gratiolet；＇7＇　certain　nerves　are　much　more　sensitive　to　tickling　than　others。　From　the　fact　that　a　child　can　hardly　tickle　itself；　or　in　a　much　less　degree　than　when　tickled　by　another　person；　it　seems　that　the　precise　point　to　be　touched　must　not　be　known；　so　with　the　mind；　something　unexpected　a　novel　or　incongruous　idea　which　breaks　through　an　habitual　train　of　thought　appears　to　he　a　strong　element　in　the　ludicrous。
  ＇6＇　J。　Lister　in　‘Quarterly　Journal　of　Microscopical　Science；'　1853；　vol。　　1。　　p。　　266。
  The　sound　of　laughter　is　produced　by　a　deep　inspiration　followed　by　short；　interrupted；　spasmodic　contractions　of　the　chest；　and　especially　of　the　diaphragm。＇8＇　Hence　we　hear　of　〃laughter　holding　both　his　sides。〃　From　the　shaking　of　the　body；　the　head　nods　to　and　fro。　　The　lower　jaw　often　quivers　up　and　down；　as　is　likewise　the　case　with　some　species　of　baboons；　when　they　are　much　pleased。
  During　laughter　the　mouth　is　opened　more　or　less　widely；　with　the　corners　drawn　much　backwards；　as　well　as　a　little　upwards；　and　the　upper　lip　is　somewhat　raised。　　The　drawing　back　of　the　corners　is　best　seen　in　moderate　laughter；　and　especially　in　a　broad　smile　the　latter　epithet　showing　how　the　mouth　is　widened。　In　the　accompanying　figs。　　1…3；　Plate　III。；　different　degrees　of　moderate　laughter　and　smiling　have　been　photographed。　The　figure　of　the　little　girl；　with　the　hat　is　by　Dr。　Wallich；　and　the　expression　was　a　genuine　one；　the　other　two　are　by　Mr。　Rejlander。　　Dr。　Duchenne　repeatedly　insists＇9＇　that；　under　the　emotion　of　joy；　the　mouth　is　acted　on　exclusively　by　the　great　zygomatic　muscles；　which　serve　to　draw　the　corners　backwards　and　upwards；　but　judging　from　the　manner　in　which　the　upper　teeth　are　always　exposed　during　laughter　and　broad　smiling；　as　well　as　from　my　own　sensations；　I　cannot　doubt　that　some　of　the　muscles　running　to　the　upper　lip　are　likewise　brought　into　moderate　action。　　The　upper　and　lower　orbicular　muscles　of　the　eyes　are　at　the　same　time　more　or　less　contracted；　and　there　is　an　intimate　connection；　as　explained　in　the　chapter　on　weeping；　between　the　orbiculars；　especially　the　lower　ones　and　some　of　the　muscles　running　to　the　upper　lip。　Henle　remarks＇10＇　on　this　head；　that　when　a　man　closely　shuts　one　eye　he　cannot　avoid　retracting　the　upper　lip　on　the　same　side；　conversely；　if　any　one　will　place　his　finger　on　his　lower　eyelid；　and　then　uncover　his　upper　incisors　as　much　as　possible；　he　will　feel；　as　his　upper　lip　is　drawn　strongly　upwards；　that　the　muscles　of　the　lower　eyelid　contract。　In　Henle's　drawing；　given　in　woodcut；　fig。　　2；　the　_musculus　malaris_　（H）　which　runs　to　the　upper　lip　may　be　seen　to　form　an　almost　integral　part　of　the　lower　orbicular　muscle。
  ＇7＇　‘De　la　Physionomie；'　p。　　186。
  ＇8＇　Sir　C。　Bell　（Anat。　of　Expression；　p。　　147）　makes　some　remarks　on　the　movement　of　the　diaphragm　during　laughter。
  ＇9＇　‘Mecanisme　de　la　Physionomie　Humaine；'　Album；　Legende　vi。
  Dr。　Duchenne　has　given　a　large　photograph　of　an　old　man　（reduced　on　Plate　III。　　fig　4）；　in　his　usual　passive　condition；　and　another　of　the　same　man　（fig。　5）；　naturally　smiling。　The　latter　was　instantly　recognized　by　every　one　to　whom　it　was　shown　as　true　to　nature。　　He　has　also　given；　as　an　example　of　an　unnatural　or　false　smile；　another　photograph　（fig。　6）　of　the　same　old　man；　with　the　corners　of　his　mouth　strongly　retracted　by　the　galvanization　of　the　great　zygomatic　muscles。　That　the　expression　is　not　natural　is　clear；　for　I　showed　this　photograph　to　twenty…four　persons；　of　whom　three　could　not　in　the　least　tell　what　was　meant；　whilst　the　others；　though　they　perceived　that　the　expression　was　of　the　nature　of　a　smile；　answered　in　such　words　as　〃a　wicked　joke；〃　〃trying　to　laugh；〃　〃grinning　laughter　。。。　。。　half…amazed　laughter；〃　&c。　Dr。　Duchenne　attributes　the　falseness　of　the　expression　altogether　to　the　orbicular　muscles　of　the　lower　eyelids　not　being　sufficiently