Therefore，inseekingfortheoriginofprotoplasm，wemusteventuallyturntothevegetableworld.Afluidcontainingcarbonicacid，water，andnitrogenoussalts，whichofferssuchaBarmecidefeast[105]totheanimal，isatablerichlyspreadtomultitudesofplants;and，withaduesupplyofonlysuchmaterials，manyaplantwillnotonlymaintainitselfinvigour，butgrowandmultiplyuntilithasincreasedamillion—fold，oramillionmillion—fold，thequantityofprotoplasmwhichitoriginallypossessed;inthiswaybuildingupthematteroflife，toanindefiniteextent，fromthecommonmatteroftheuniverse.
Thus，theanimalcanonlyraisethecomplexsubstanceofdeadprotoplasmtothehigherpower，asonemaysay，oflivingprotoplasm;whiletheplantcanraisethelesscomplexsubstances——
carbonicacid，water，andnitrogenoussalts——tothesamestageoflivingprotoplasm，ifnottothesamelevel.Buttheplantalsohasitslimitations.Someofthefungi，forexample，appeartoneedhighercompoundstostartwith;andnoknownplantcanliveupontheuncompoundedelementsofprotoplasm.Aplantsuppliedwithpurecarbon，hydrogen，oxygen，andnitrogen，phosphorus，sulphur，andthelike，wouldasinfalliblydieastheanimalinhisbathofsmelling—salts，thoughitwouldbesurroundedbyalltheconstituentsofprotoplasm.Nor，indeed，needtheprocessofsimplificationofvegetablefoodbecarriedsofarasthis，inordertoarriveatthelimitoftheplant’sthaumaturgy.Letwater，carbonicacid，andalltheotherneedfulconstituentsbesuppliedexceptnitrogenoussalts，andanordinaryplantwillstillbeunabletomanufactureprotoplasm.
Thusthematteroflife，sofarasweknowit（andwehavenorighttospeculateonanyother），breaksup，inconsequenceofthatcontinualdeathwhichistheconditionofitsmanifestingvitality，intocarbonicacid，water，andnitrogenouscompounds，whichcertainlypossessnopropertiesbutthoseofordinarymatter.Andoutofthesesameformsofordinarymatter，andfromnonewhicharesimpler，thevegetableworldbuildsupalltheprotoplasmwhichkeepstheanimalworlda—going.Plantsaretheaccumulatorsofthepowerwhichanimalsdistributeanddisperse.
Butitwillbeobserved，thattheexistenceofthematteroflifedependsonthepre—existenceofcertaincompounds;namely，carbonicacid，water，andcertainnitrogenousbodies.Withdrawanyoneofthesethreefromtheworld，andallvitalphaenomenacometoanend.Theyareasnecessarytotheprotoplasmoftheplant，astheprotoplasmoftheplantistothatoftheanimal.Carbon，hydrogen，oxygen，andnitrogenarealllifelessbodies.Ofthese，carbonandoxygenuniteincertainproportionsandundercertainconditions，togiverisetocarbonicacid;hydrogenandoxygenproducewater;nitrogenandotherelementsgiverisetonitrogenoussalts.Thesenewcompounds，liketheelementarybodiesofwhichtheyarecomposed，arelifeless.Butwhentheyarebroughttogether，undercertainconditions，theygiverisetothestillmorecomplexbody，protoplasm，andthisprotoplasmexhibitsthephaenomenaoflife.