ntery；　and　in　other　tropical　diseases　protozoa　were　discovered；　so　that　we　were　really　prepared　for　the　announcement　in　1905；　by　Schaudinn；　of　the　discovery　of　a　protozoan　parasite　in　syphilis。　Just　fifty　years　had　passed　since　Pasteur　had　sent　in　his　paper　on　〃Lactic　Acid　Fermentation〃　to　the　Lille　Scientific　Societyhalf　a　century　in　which　more　had　been　done　to　determine　the　true　nature　of　disease　than　in　all　the　time　that　had　passed　since　Hippocrates。　　Celsus　makes　the　oft…quoted　remark　that　to　determine　the　cause　of　a　disease　often　leads　to　the　remedy；＇*＇　and　it　is　the　possibility　of　removing　the　cause　that　gives　such　importance　to　the　new　researches　on　disease。
  ＇*＇　〃Et　causae　quoque　estimatio　saepe　morbum　solvit；〃　Celsus；　Lib。　　I；　Prefatio。Ed。
  INTERNAL　SECRETIONS
  ONE　of　the　greatest　contributions　of　the　nineteenth　century　to　scientific　medicine　was　the　discovery　of　the　internal　secretions　of　organs。　The　basic　work　on　the　subject　was　done　by　Claude　Bernard；　a　pupil　of　the　great　Magendie；　whose　saying　it　is　well　to　remember〃When　entering　a　laboratory　one　should　leave　theories　in　the　cloakroom。〃　More　than　any　other　man　of　his　generation；　Claude　Bernard　appreciated　the　importance　of　experiment　in　practical　medicine。　For　him　the　experimental　physician　was　the　physician　of　the　future　a　view　well　borne　out　by　the　influence　his　epoch…making　work　has　had　on　the　treatment　of　disease。　　His　studies　on　the　glycogenic　functions　of　the　liver　opened　the　way　for　the　modern　fruitful　researches　on　the　internal　secretions　of　the　various　glands。　About　the　same　time　that　Bernard　was　developing　the　laboratory　side　of　the　problem；　Addison；　a　physician　to　Guy's　Hospital；　in　1855；　pointed　out　the　relation　of　a　remarkable　group　of　symptoms　to　disease　of　the　suprarenal　glands；　small　bodies　situated　above　the　kidneys；　the　importance　of　which　had　not　been　previously　recognized。　With　the　loss　of　the　function　of　these　glands　by　disease；　the　body　was　deprived　of　something　formed　by　them　which　was　essential　to　its　proper　working。　　Then；　in　the　last　third　of　the　century；　came　in　rapid　succession　the　demonstration　of　the　relations　of　the　pancreas　to　diabetes；　of　the　vital　importance　of　the　thyroid　gland　and　of　the　pituitary　body。　Perhaps　no　more　striking　illustration　of　the　value　of　experimental　medicine　has　ever　been　given　than　that　afforded　by　the　studies　upon　those　glands。
  The　thyroid　body；　situated　in　the　neck　and　the　enlargement　of　which　is　called　goitre；　secretes　substances　which　pass　into　the　blood；　and　which　are　necessary　for　the　growth　of　the　body　in　childhood；　for　the　development　of　the　mind　and　for　the　nutrition　of　the　tissues　of　the　skin。　　If；　following　an　infectious　disease；　a　child　has　wasting　of　this　gland；　or　if；　living　in　a　certain　district；　it　has　a　large　goitre；　normal　development　does　not　take　place；　and　the　child　does　not　grow　in　mind　or　body　and　becomes　what　is　called　a　cretin。　More　than　thisif　in　adult　life　the　gland　is　completely　removed；　or　if　it　wastes；　a　somewhat　similar　condition　is　produced；　and　the　patient　in　time　loses　his　mental　powers　and　becomes　fat　and　flabbymyxedematous。　　It　has　been　shown　experimentally　in　various　ways　that　the　necessary　elements　of　the　secretion　can　be　furnished　by　feeding　with　the　gland　or　its　extracts；　and　that　the　cretinoid　or　myxedematous　conditions　could　thus　be　cured　or　prevented。
  Experimental　work　has　also　demonstrated　the　functions　of　the　suprarenal　glands　and　explained　the　symptoms　of　Addison's　disease；　and　chemists　have　even　succeeded　in　making　synthetically　the　active　principle　adrenalin。
  There　is　perhaps　no　more　fascinating　story　in　the　history　of　science　than　that　of　the　discovery　of　these　so…called　ductless　glands。　Part　of　its　special　interest　is　due　to　the　fact　that　clinicians；　surgeons；　experimental　physiologists；　pathologists　and　chemists　have　all　combined　in　splendid　teamwork　to　win　the　victory。　No　such　miracles　have　ever　before　been　wrought　by　physicians　as　those　which　we　see　in　connection　with　the　internal　secretion　of　the　thyroid　gland。　　The　myth　of　bringing　the　dead　back　to　life　has　been　associated　with　the　names　of　many　great　healers　since　the　incident　of　Empedocles　and　Pantheia；　but　nowadays　the　dead　in　mind　and　the　deformed　in　body　may　be　restored　by　the　touch　of　the　magic　wand　of　science。　The　study　of　the　interaction　of　these　internal　secretions；　their　influence　upon　development；　upon　mental　process　and　upon　disorders　of　metabolism　is　likely　to　prove　in　the　future　of　a　benefit　scarcely　less　remarkable　than　that　which　we　have　traced　in　the　infectious　diseases。
  CHEMISTRY
  IT　is　not　making　too　strong　a　statement　to　say　that　the　chemistry　and　chemical　physics　of　the　nineteenth　century　have　revolutionized　the　world。　It　is　difficult　to　realize　that　Liebig's　famous　Giessen　laboratory；　the　first　to　be　opened　to　students　for　practical　study；　was　founded　in　the　year　1825。　Boyle；　Cavendish；　Priestley；　Lavoisier；　Black；　Dalton　and　others　had　laid　a　broad　foundation；　and　Young；　Frauenhofer；　Rumford；　Davy；　Joule；　Faraday；　Clerk…Maxwell；　Helmholtz　and　others　built　upon　that　and　gave　us　the　new　physics　and　made　possible　our　age　of　electricity。　　New　technique　and　new　methods　have　given　a　powerful　stimulus　to　the　study　of　the　chemical　changes　that　take　place　in　the　body；　which；　only　a　few　years　ago；　were　matters　largely　of　speculation。　　〃Now；〃　in　the　words　of　Professor　Lee；　〃we　recognize　that；　with　its　living　and　its　non…living　substances　inextricably　intermingled；　the　body　constitutes　an　intensive　chemical　laboratory　in　which　there　is　ever　occurring　a　vast　congeries　of　chemical　reactions；　both　constructive　and　destructive　processes　go　on；　new　protoplasm　takes　the　place　of　old。　We　can　analyze　the　income　of　the　body　and　we　can　analyze　its　output；　and　from　these　data　we　can　learn　much　concerning　the　body's　chemistry。　A　great　improvement　in　the　method　of　such　work　has　recently　been　secured　by　the　device　of　inclosing　the　person　who　is　the　subject　of　the　experiment　in　a　respiration　calorimeter。　　This　is　an　air…tight　chamber；　artificially　supplied　with　a　constant　stream　of　pure　air；　and　from　which　the　expired　air；　laden　with　the　products　of　respiration；　is　withdrawn　for　purposes　of　analysis。　The　subject　may　remain　in　the　chamber　for　days；　the　composition　of　all　food　and　all　excrete　being　determined；　and　all　heat　that　is　given　off　being　measured。　Favorable　conditions　are　thus　established　for　an　exact　study　of　many　problems　of　nutrition。　　The　difficulties　increase　when　we　attempt　to　trace　the　successive　steps　in　the　corporeal　pathway　of　molecule　and　atom。　Yet　these　secrets　of　the　vital　process　are　also　gradually　being　revealed。　When　we　remember　that　it　is　in　this　very　field　of　nutrition　that　there　exist　great　popular　ignorance　and　a　special　proneness　to　fad　and　prejudice；　we　realize　how　practically　helpful　are　such　exact　studies　of　metabolism。〃＇13＇
  ＇13＇　Frederick　S。　Lee；　Ph。D。：　Scientific　Features　of　Modern　Medicine；　New　York；　1911。　　I　would　like　to　call　attention　to　this　work　of　Professor　Lee's　as　presenting　all　the　scientific　features　of　modern　medicine　in　a　way　admirably　adapted　for　anyone；　lay　or　medical；　who　wishes　to　get　a　clear　sketch　of　them。
  CHAPTER　VI
  THE　RISE　OF　PREVENTIVE　MEDICINE
  THE　story　so　far　has　been　of　men　and　of　movementsof　men　who　have；　consciously　or　unconsciously；　initiated　great　movements；　and　of　movements　by　which；　nolens　volens；　the　men　of　the　time　were　moulded　and　controlled。　Hippocrates；　in　the　tractate　on　〃Ancient　Medicine；〃　has　a　splendid　paragraph　on　the　attitude　of　mind　towards　the　men　of　the　past。　My　attention　was　called　to　it　one　day　in　the　Roman　Forum　by　Commendatore　Boni；　who　quoted　it　as　one　of　the　great　sayings　of　antiquity。　　Here　it　is：　〃But　on　that　account；　I　say；　we　ought　not　to　reject　the　ancient　Art；　as　if　it　were　not；　and　had　not　been　properly　founded；　because　it　did　not　attain　accuracy　in　all　things；　but　rather；　since　it　is　capable　of　reaching　to　the　greatest　exactitude　by　reasoning；　to　receive　it　and　admire　its　discoveries；　made　from　a　state　of　great　ignorance；　and　as　having　been　well　and　properly　made；　and　not　from　chance。〃＇1＇
  ＇1＇　The　Works　of　Hippocrates；　Adams；　Vol。　I；　p。　168；　London；　1849　（Sydenham　Society）。
  I　have　tried　to　tell　you　what　the　best　of　these　men　in　successive　ages　knew；　to　show　you　their　point　of　outlook　on　the　things　that　interest　us。　To　understand　the　old　writers　one　must　see　as　they　saw；　feel　as　they　felt；　believe　as　they　believedand　this　is　hard；　indeed　impossible！　We　may　get　near　them　by　asking　the　Spirit　of　the　Age　in　which　they　lived　to　enter　in　and　dwell　with　us；　but　it　does　not　always　come。　Literary　criticism　is　not　literary　historywe　have　no　use　here　for　the　former；　but　to　analyze　his　writings　is　to　get　as　far　as　we　can　behind　the　doors　of　a　man's　mind；　to　know　and　appraise　his　knowledge；　not　from　our　standpoint；　but　from　that　of　his　contemporaries；　his　predecessors　and　his　immediate　successors。　　Each　generation　has　its　own　problems　to　face；　looks　at　truth　from　a　special　focus　and　does　not　see　quite　the　same　outlines　as　any　other。　For　example；　men　of　the　present　generation　grow　up　under　influences　very　different　from　those　which　surrounded　my　generation　in　the　seventies　of　the　last　century；　wh