Justatthecloseofthecenturytherecameintoprominencetheschoolofhomoeopathy，whichwasdestinedtoinfluencethepracticeofmedicineverymateriallyandtooutlivealltheothereighteenth-centuryschools。ItwasfoundedbyChristianSamuelFriedrichHahnemann1755-1843，amostremarkableman，who，afterpropoundingatheoryinhisyoungerdayswhichwasatleastasreasonableasmostoftheexistingtheories，hadthemisfortunetooutlivehisusefulnessandlayhisdoctrineopentoridiculebytheunreasonableteachingsofhisdotage，Hahnemannrejectedalltheteachingsofmorbidanatomyandpathologyasuselessinpractice，andpropoundedhisfamous\"similiasimilibuscurantur\"——thatalldiseasesweretobecuredbymedicinewhichinhealthproducedsymptomsdynamicallysimilartothediseaseundertreatment。Ifacertainmedicineproducedaheadachewhengiventoahealthyperson，thenthismedicinewasindicatedincaseofheadaches，etc。Atthepresenttimesuchatheoryseemscrudeenough，butinthelatterpartoftheeighteenthcenturyalmostanytheorywasasgoodastheonespropoundedbyAnimists，Vitalists，andothersuchschools。Itcertainlyhadtheverycommendablefeatureofintroducingsimplicityintheuseofdrugsinplaceofthecomplicatedprescriptionstheninvogue。HadHahnemannstoppedatthispointhecouldnothavebeenhelduptotheindefensibleridiculethatwasbroughtuponhim，withconsiderablejustice，byhislatertheories。Buthelivedontopropoundhisextraordinarytheoryof\"potentiality\"——thatmedicinesgainedstrengthbybeingdiluted——andhisevenmoreextraordinarytheorythatallchronicdiseasesarecausedeitherbytheitch，syphilis，orfig-wartdisease，orarebroughtonbymedicines。
Atthetimethathistheoryofpotentialitieswaspromulgated，themedicalworldhadgonemadinitsadministrationofhugedosesofcompoundmixturesofdrugs，andanyreactionagainstthiswassurelyanimprovement。Inshort，nomedicineatallwasmuchbetterthantheheapingdosesusedincommonpractice；andhenceoneadvantage，atleast，ofHahnemann’smethods。Statedbriefly，histheorywasthatifatincturebereducedtoone-fiftiethinstrength，andthisagainreducedtoone-fiftieth，andthisprocessrepeateduptothirtysuchdilutions，thepotencyofsuchamedicinewillbeincreasedbyeachdilution，Hahnemannhimselfpreferringtheweakest，or，ashewouldcallit，thestrongestdilution。Theabsurdityofsuchatheoryisapparentwhenitisunderstoodthatlongbeforeanydrughasbeenraisedtoitsthirtiethdilutionithasbeensoreducedinquantitythatitcannotbeweighed，measured，orrecognizedasbeingpresentinthesolutionatallbyanymeansknowntochemists。Itisbutjusttomodernfollowersofhomoeopathytosaythatwhilemostofthemadvocatesmalldosage，theydonotnecessarilyfollowtheteachingsofHahnemanninthisrespect，believingthatthetheoryofthedose\"hasnothingmoretodowiththeoriginallawofcurethanthepsoraitchtheoryhas；
andthatitwasoneofthelatercreationsofHahnemann’smind。\"
Hahnemann’stheorythatallchronicdiseasesarederivedfromeitheritch，syphilis，orfig-wartdiseaseisnolongeradvocatedbyhisfollowers，becauseitissoeasilydisproved，particularlyinthecaseofitch。Hahnemanntaughtthatfullythree-quartersofalldiseaseswerecausedby\"itchstruckin，\"andyetithadbeendemonstratedlongbeforehisday，andcanbedemonstratedanytime，thatitchissimplyalocalskindiseasecausedbyasmallparasite。
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