aggregation。
  Thus　a　nucleated　mass　of　protoplasm　turns　out　to　be　what　may　be
  termed　the　structural　unit　of　the　human　body。　　As　a　matter　of　fact；
  the　body；　in　its　earliest　state；　is　a　mere　multiple　of　such　units；
  and　in　its　perfect　condition；　it　is　a　multiple　of　such　units；
  variously　modified。
  But　does　the　formula　which　expresses　the　essential　structural
  character　of　the　highest　animal　cover　all　the　rest；　as　the
  statement　of　its　powers　and　faculties　covered　that　of　all　others？
  Very　nearly。　　Beast　and　fowl；　reptile　and　fish；　mollusk；　worm；　and
  polype；　are　all　composed　of　structural　units　of　the　same　character；
  namely；　masses　of　protoplasm　with　a　nucleus。　　There　are　sundry　very
  low　animals；　each　of　which；　structurally；　is　a　mere　colourless
  blood…corpuscle；　leading　an　independent　life。　　But；　at　the　very
  bottom　of　the　animal　scale；　even　this　simplicity　becomes
  simplified；　and　all　the　phaenomena　of　life　are　manifested　by　a
  particle　of　protoplasm　without　a　nucleus。　　Nor　are　such　organisms
  insignificant　by　reason　of　their　want　of　complexity。　　It　is　a　fair
  question　whether　the　protoplasm　of　those　simplest　forms　of　life；
  which　people　an　immense　extent　of　the　bottom　of　the　sea；　would　not
  outweigh　that　of　all　the　higher　living　beings　which　inhabit　the
  land　put　together。　　And　in　ancient　times；　no　less　than　at　the
  present　day；　such　living　beings　as　these　have　been　the　greatest　of
  rock　builders。
  What　has　been　said　of　the　animal　world　is　no　less　true　of　plants。
  Imbedded　in　the　protoplasm　at　the　broad；　or　attached；　end　of　the
  nettle　hair；　there　lies　a　spheroidal　nucleus。　　Careful　examination
  further　proves　that　the　whole　substance　of　the　nettle　is　made　up　of
  a　repetition　of　such　masses　of　nucleated　protoplasm；　each　contained
  in　a　wooden　case；　which　is　modified　in　form；　sometimes　into　a　woody
  fibre；　sometimes　into　a　duct　or　spiral　vessel；　sometimes　into　a
  pollen　grain；　or　an　ovule。　　Traced　back　to　its　earliest　state；　the
  nettle　arises　as　the　man　does；　in　a　particle　of　nucleated
  protoplasm。　　And　in　the　lowest　plants；　as　in　the　lowest　animals；　a
  single　mass　of　such　protoplasm　may　constitute　the　whole　plant；　or
  the　protoplasm　may　exist　without　a　nucleus。
  Under　these　circumstances　it　may　well　be　asked；　how　is　one　mass　of
  non…nucleated　protoplasm　to　be　distinguished　from　another？　why　call
  one　〃plant〃　and　the　other　〃animal〃？
  The　only　reply　is　that；　so　far　as　form　is　concerned；　plants　and
  animals　are　not　separable；　and　that；　in　many　cases；　it　is　a　mere
  matter　of　convention　whether　we　call　a　given　organism　an　animal　or
  a　plant。　　There　is　a　living　body　called　Aethalium　septicum；　which
  appears　upon　decaying　vegetable　substances；　and；　in　one　of　its
  forms；　is　common　upon　the　surfaces　of　tan…pits。　　In　this　condition
  it　is；　to　all　intents　and　purposes；　a　fungus；　and　formerly　was
  always　regarded　as　such；　but　the　remarkable　investigations　of　De
  Bary　＇99＇　have　shown　that；　in　another　condition；　the　Aethalium　is　an
  actively　locomotive　creature；　and　takes　in　solid　matters；　upon
  which；　apparently；　it　feeds；　thus　exhibiting　the　most　characteristic
  feature　of　animality。　　Is　this　a　plant；　or　is　it　an　animal？
  Is　it　both；　or　is　it　neither？　　Some　decide　in　favour　of　the　last
  supposition；　and　establish　an　intermediate　kingdom；　a　sort
  of　biological　No　Man's　Land　＇100＇　for　all　these　questionable　forms。
  But；　as　it　is　admittedly　impossible　to　draw　any　distinct　boundary　line
  between　this　no　man's　land　and　the　vegetable　world　on　the　one　hand；
  or　the　animal；　on　the　other；　it　appears　to　me　that　this　proceeding
  merely　doubles　the　difficulty　which；　before；　was　single。
  Protoplasm；　simple　or　nucleated；　is　the　formal　basis　of　all　life。
  It　is　the　clay　of　the　potter：　which；　bake　it　and　paint　it　as　he
  will；　remains　clay；　separated　by　artifice；　and　not　by　nature；　from
  the　commonest　brick　or　sun…dried　clod。
  Thus　it　becomes　clear　that　all　living　powers　are　cognate；　and
  that　all　living　forms　are　fundamentally　of　one　character。　　The
  researches　of　the　chemist　have　revealed　a　no　less　striking
  uniformity　of　material　composition　in　living　matter。
  In　perfect　strictness；　it　is　true　that　chemical　investigation　can
  tell　us　little　or　nothing；　directly；　of　the　composition　of　living
  matter；　inasmuch　as　such　matter　must　needs　die　in　the　act　of
  analysis；and　upon　this　very　obvious　ground；　objections；　which　I
  confess　seem　to　me　to　be　somewhat　frivolous；　have　been　raised　to
  the　drawing　of　any　conclusions　whatever　respecting　the　composition
  of　actually　living　matter；　from　that　of　the　dead　matter　of　life；
  which　alone　is　accessible　to　us。　　But　objectors　of　this　class　do
  not　seem　to　reflect　that　it　is　also；　in　strictness；　true　that　we
  know　nothing　about　the　composition　of　any　body　whatever；　as　it　is。
  The　statement　that　a　crystal　of　calc…spar　consists　of　carbonate　of
  lime；　is　quite　true；　if　we　only　mean　that；　by　appropriate
  processes；　it　may　be　resolved　into　carbonic　acid　and　quicklime。　　If
  you　pass　the　same　carbonic　acid　over　the　very　quicklime　thus
  obtained；　you　will　obtain　carbonate　of　lime　again；　but　it　will　not
  be　calc…spar；　nor　anything　like　it。　　Can　it；　therefore；　be　said
  that　chemical　analysis　teaches　nothing　about　the　chemical
  composition　of　calc…spar？　　Such　a　statement　would　be　absurd；　but　it
  is　hardly　more　so　than　the　talk　one　occasionally　hears　about　the
  uselessness　of　applying　the　results　of　chemical　analysis　to　the
  living　bodies　which　have　yielded　them。
  One　fact；　at　any　rate；　is　out　of　reach　of　such　refinements；　and
  this　is；　that　all　the　forms　of　protoplasm　which　have　yet　been
  examined　contain　the　four　elements；　carbon；　hydrogen；　oxygen；　and
  nitrogen；　in　very　complex　union；　and　that　they　behave　similarly
  towards　several　reagents。　　To　this　complex　combination；　the　nature
  of　which　has　never　been　determined　with　exactness；　the　name　of
  Protein　has　been　applied。　　And　if　we　use　this　term　with　such
  caution　as　may　properly　arise　out　of　our　comparative　ignorance　of
  the　things　for　which　it　stands；　it　may　be　truly　said；　that　all
  protoplasm　is　proteinaceous；　or；　as　the　white；　or　albumen；　of　an
  egg　is　one　of　the　commonest　examples　of　a　nearly　pure　proteine
  matter；　we　may　say　that　all　living　matter　is　more　or　less
  albuminoid。
  Perhaps　it　would　not　yet　be　safe　to　say　that　all　forms　of
  protoplasm　are　affected　by　the　direct　action　of　electric　shocks；
  and　yet　the　number　of　cases　in　which　the　contraction　of　protoplasm
  is　shown　to　be　affected　by　this　agency　increases　every　day。
  Nor　can　it　be　affirmed　with　perfect　confidence；　that　all　forms　of
  protoplasm　are　liable　to　undergo　that　peculiar　coagulation　at　a
  temperature　of　40…50　degrees　centigrade；　which　has　been　called
  〃heat…stiffening；〃　though　Kuhne's　＇101＇　beautiful　researches　have
  proved　this　occurrence　to　take　place　in　so　many　and　such　diverse
  living　beings；　that　it　is　hardly　rash　to　expect　that　the　law　holds
  good　for　all。
  Enough　has；　perhaps；　been　said　to　prove　the　existence　of　a　general
  uniformity　in　the　character　of　the　protoplasm；　or　physical　basis；
  of　life；　in　whatever　group　of　living　beings　it　may　be　studied。　　But
  it　will　be　understood　that　this　general　uniformity　by　no　means
  excludes　any　amount　of　special　modifications　of　the　fundamental
  substance。　　The　mineral；　carbonate　of　lime；　assumes　an　immense
  diversity　of　characters；　though　no　one　doubts　that；　under　all　these
  Protean　changes；　it　is　one　and　the　same　thing。
  And　now；　what　is　the　ultimate　fate；　and　what　the　origin；　of　the
  matter　of　life？
  Is　it；　as　some　of　the　older　naturalists　supposed；　diffused
  throughout　the　universe　in　molecules；　which　are　indestructible　and
  unchangeable　in　themselves；　but；　in　endless　transmigration；　unite
  in　innumerable　permutations；　into　the　diversified　forms　of　life　we
  know？　　Or；　is　the　matter　of　life　composed　of　ordinary　matter；
  differing　from　it　only　in　the　manner　in　which　its　atoms　are
  aggregated？　　Is　it　built　up　of　ordinary　matter；　and　again　resolved
  into　ordinary　matter　when　its　work　is　done？
  Modern　science　does　not　hesitate　a　moment　between　these
  alternatives。　　Physiology　writes　over　the　portals　of　life
  〃Debemur　morti　nos　nostraque；〃＇102＇
  with　a　profounder　meaning　than　the　Roman　poet　attached　to　that
  melancholy　line。　　Under　whatever　disguise　it　takes　refuge；　whether
  fungus　or　oak；　worm　or　man；　the　living　protoplasm　not　only
  ultimately　dies　and　is　resolved　into　its　mineral　and　lifeless
  constituents；　but　is　always　dying；　and；　strange　as　the　paradox　may
  sound；　could　not　live　unless　it　died。
  In　the　wonderful　story　of　the　Peau　de　Chagrin；＇103＇　the　hero　becomes
  possessed　of　a　magical　wild　ass'　skin；　which　yields　him　the　means
  of　gratifying　all　his　wishes。　　But　its　surface　represents　the
  duration　of　the　proprietor's　life；　and　for　every　satisfied　desire
  the　skin　shrinks　in　proportion　to　the　intensity　of　fruition；　until
  at　length　life　and　the　last　handbreadth　of　the　peau　de　chagrin；
  disappear　with　th