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perimented¡¡with¡¡frogs£»¡¡tortoises£»¡¡and¡¡dogs£»¡¡and¡¡settled¡¡beyond¡¡question¡¡the¡¡function¡¡of¡¡the¡¡ovum¡¡and¡¡spermatozoon¡£¡¡Unfortunately¡¡he¡¡misinterpreted¡¡the¡¡part¡¡played¡¡by¡¡the¡¡spermatozoa¡¡in¡¡believing¡¡that¡¡their¡¡surrounding¡¡fluid¡¡was¡¡equally¡¡active¡¡in¡¡the¡¡fertilizing¡¡process£»¡¡and¡¡it¡¡was¡¡not¡¡until¡¡some¡¡forty¡¡years¡¡later¡¡£¨1824£©¡¡that¡¡Dumas¡¡corrected¡¡this¡¡error¡£


THE¡¡CHEMICAL¡¡THEORY¡¡OF¡¡DIGESTION

Among¡¡the¡¡most¡¡interesting¡¡researches¡¡of¡¡Spallanzani¡¡were¡¡his¡¡experiments¡¡to¡¡prove¡¡that¡¡digestion£»¡¡as¡¡carried¡¡on¡¡in¡¡the¡¡stomach£»¡¡is¡¡a¡¡chemical¡¡process¡£¡¡¡¡In¡¡this¡¡he¡¡demonstrated£»¡¡as¡¡Rene¡¡Reaumur¡¡had¡¡attempted¡¡to¡¡demonstrate£»¡¡that¡¡digestion¡¡could¡¡be¡¡carried¡¡on¡¡outside¡¡the¡¡walls¡¡of¡¡the¡¡stomach¡¡as¡¡an¡¡ordinary¡¡chemical¡¡reaction£»¡¡using¡¡the¡¡gastric¡¡juice¡¡as¡¡the¡¡reagent¡¡for¡¡performing¡¡the¡¡experiment¡£¡¡The¡¡question¡¡as¡¡to¡¡whether¡¡the¡¡stomach¡¡acted¡¡as¡¡a¡¡grinding¡¡or¡¡triturating¡¡organ£»¡¡rather¡¡than¡¡as¡¡a¡¡receptacle¡¡for¡¡chemical¡¡action£»¡¡had¡¡been¡¡settled¡¡by¡¡Reaumur¡¡and¡¡was¡¡no¡¡longer¡¡a¡¡question¡¡of¡¡general¡¡dispute¡£¡¡Reaumur¡¡had¡¡demonstrated¡¡conclusively¡¡that¡¡digestion¡¡would¡¡take¡¡place¡¡in¡¡the¡¡stomach¡¡in¡¡the¡¡same¡¡manner¡¡and¡¡the¡¡same¡¡time¡¡if¡¡the¡¡substance¡¡to¡¡be¡¡digested¡¡was¡¡protected¡¡from¡¡the¡¡peristalic¡¡movements¡¡of¡¡the¡¡stomach¡¡and¡¡subjected¡¡to¡¡the¡¡action¡¡of¡¡the¡¡gastric¡¡juice¡¡only¡£¡¡He¡¡did¡¡this¡¡by¡¡introducing¡¡the¡¡substances¡¡to¡¡be¡¡digested¡¡into¡¡the¡¡stomach¡¡in¡¡tubes£»¡¡and¡¡thus¡¡protected¡¡so¡¡that¡¡while¡¡the¡¡juices¡¡of¡¡the¡¡stomach¡¡could¡¡act¡¡upon¡¡them¡¡freely¡¡they¡¡would¡¡not¡¡be¡¡affected¡¡by¡¡any¡¡movements¡¡of¡¡the¡¡organ¡£

Following¡¡up¡¡these¡¡experiments£»¡¡he¡¡attempted¡¡to¡¡show¡¡that¡¡digestion¡¡could¡¡take¡¡place¡¡outside¡¡the¡¡body¡¡as¡¡well¡¡as¡¡in¡¡it£»¡¡as¡¡it¡¡certainly¡¡should¡¡if¡¡it¡¡were¡¡a¡¡purely¡¡chemical¡¡process¡£¡¡He¡¡collected¡¡quantities¡¡of¡¡gastric¡¡juice£»¡¡and¡¡placing¡¡it¡¡in¡¡suitable¡¡vessels¡¡containing¡¡crushed¡¡grain¡¡or¡¡flesh£»¡¡kept¡¡the¡¡mixture¡¡at¡¡about¡¡the¡¡temperature¡¡of¡¡the¡¡body¡¡for¡¡several¡¡hours¡£¡¡After¡¡repeated¡¡experiments¡¡of¡¡this¡¡kind£»¡¡apparently¡¡conducted¡¡with¡¡great¡¡care£»¡¡Reaumur¡¡reached¡¡the¡¡conclusion¡¡that¡¡¡¨the¡¡gastric¡¡juice¡¡has¡¡no¡¡more¡¡effect¡¡out¡¡of¡¡the¡¡living¡¡body¡¡in¡¡dissolving¡¡or¡¡digesting¡¡the¡¡food¡¡than¡¡water£»¡¡mucilage£»¡¡milk£»¡¡or¡¡any¡¡other¡¡bland¡¡fluid¡£¡¨£§3£§¡¡Just¡¡why¡¡all¡¡of¡¡these¡¡experiments¡¡failed¡¡to¡¡demonstrate¡¡a¡¡fact¡¡so¡¡simple¡¡does¡¡not¡¡appear£»¡¡but¡¡to¡¡Spallanzani£»¡¡at¡¡least£»¡¡they¡¡were¡¡by¡¡no¡¡means¡¡conclusive£»¡¡and¡¡he¡¡proceeded¡¡to¡¡elaborate¡¡upon¡¡the¡¡experiments¡¡of¡¡Reaumur¡£¡¡¡¡He¡¡made¡¡his¡¡experiments¡¡in¡¡scaled¡¡tubes¡¡exposed¡¡to¡¡a¡¡certain¡¡degree¡¡of¡¡heat£»¡¡and¡¡showed¡¡conclusively¡¡that¡¡the¡¡chemical¡¡process¡¡does¡¡go¡¡on£»¡¡even¡¡when¡¡the¡¡food¡¡and¡¡gastric¡¡juice¡¡are¡¡removed¡¡from¡¡their¡¡natural¡¡environment¡¡in¡¡the¡¡stomach¡£¡¡In¡¡this¡¡he¡¡was¡¡opposed¡¡by¡¡many¡¡physiologists£»¡¡among¡¡them¡¡John¡¡Hunter£»¡¡but¡¡the¡¡truth¡¡of¡¡his¡¡demonstrations¡¡could¡¡not¡¡be¡¡shaken£»¡¡and¡¡in¡¡later¡¡years¡¡we¡¡find¡¡Hunter¡¡himself¡¡completing¡¡Spallanzani's¡¡experiments¡¡by¡¡his¡¡studies¡¡of¡¡the¡¡post¡­mortem¡¡action¡¡of¡¡the¡¡gastric¡¡juice¡¡upon¡¡the¡¡stomach¡¡walls¡£

That¡¡Spallanzani's¡¡and¡¡Hunter's¡¡theories¡¡of¡¡the¡¡action¡¡of¡¡the¡¡gastric¡¡juice¡¡were¡¡not¡¡at¡¡once¡¡universally¡¡accepted¡¡is¡¡shown¡¡by¡¡an¡¡essay¡¡written¡¡by¡¡a¡¡learned¡¡physician¡¡in¡¡1834¡£¡¡In¡¡speaking¡¡of¡¡some¡¡of¡¡Spallanzani's¡¡demonstrations£»¡¡he¡¡writes£º¡¡¡¨In¡¡some¡¡of¡¡the¡¡experiments£»¡¡in¡¡order¡¡to¡¡give¡¡the¡¡flesh¡¡or¡¡grains¡¡steeped¡¡in¡¡the¡¡gastric¡¡juice¡¡the¡¡same¡¡temperature¡¡with¡¡the¡¡body£»¡¡the¡¡phials¡¡were¡¡introduced¡¡under¡¡the¡¡armpits¡£¡¡But¡¡this¡¡is¡¡not¡¡a¡¡fair¡¡mode¡¡of¡¡ascertaining¡¡the¡¡effects¡¡of¡¡the¡¡gastric¡¡juice¡¡out¡¡of¡¡the¡¡body£»¡¡for¡¡the¡¡influence¡¡which¡¡life¡¡may¡¡be¡¡supposed¡¡to¡¡have¡¡on¡¡the¡¡solution¡¡of¡¡the¡¡food¡¡would¡¡be¡¡secured¡¡in¡¡this¡¡case¡£¡¡¡¡The¡¡affinities¡¡connected¡¡with¡¡life¡¡would¡¡extend¡¡to¡¡substances¡¡in¡¡contact¡¡with¡¡any¡¡part¡¡of¡¡the¡¡system£º¡¡substances¡¡placed¡¡under¡¡the¡¡armpits¡¡are¡¡not¡¡placed¡¡at¡¡least¡¡in¡¡the¡¡same¡¡circumstances¡¡with¡¡those¡¡unconnected¡¡with¡¡a¡¡living¡¡animal¡£¡¨¡¡But¡¡just¡¡how¡¡this¡¡writer¡¡reaches¡¡the¡¡conclusion¡¡that¡¡¡¨the¡¡experiments¡¡of¡¡Reaumur¡¡and¡¡Spallanzani¡¡give¡¡no¡¡evidence¡¡that¡¡the¡¡gastric¡¡juice¡¡has¡¡any¡¡peculiar¡¡influence¡¡more¡¡than¡¡water¡¡or¡¡any¡¡other¡¡bland¡¡fluid¡¡in¡¡digesting¡¡the¡¡food¡¨£§4£§¡¡is¡¡difficult¡¡to¡¡understand¡£

The¡¡concluding¡¡touches¡¡were¡¡given¡¡to¡¡the¡¡new¡¡theory¡¡of¡¡digestion¡¡by¡¡John¡¡Hunter£»¡¡who£»¡¡as¡¡we¡¡have¡¡seen£»¡¡at¡¡first¡¡opposed¡¡Spallanzani£»¡¡but¡¡who¡¡finally¡¡became¡¡an¡¡ardent¡¡champion¡¡of¡¡the¡¡chemical¡¡theory¡£¡¡Hunter¡¡now¡¡carried¡¡Spallanzani's¡¡experiments¡¡further¡¡and¡¡proved¡¡the¡¡action¡¡of¡¡the¡¡digestive¡¡fluids¡¡after¡¡death¡£¡¡For¡¡many¡¡years¡¡anatomists¡¡had¡¡been¡¡puzzled¡¡by¡¡pathological¡¡lesion¡¡of¡¡the¡¡stomach£»¡¡found¡¡post¡¡mortem£»¡¡when¡¡no¡¡symptoms¡¡of¡¡any¡¡disorder¡¡of¡¡the¡¡stomach¡¡had¡¡been¡¡evinced¡¡during¡¡life¡£¡¡Hunter¡¡rightly¡¡conceived¡¡that¡¡these¡¡lesions¡¡were¡¡caused¡¡by¡¡the¡¡action¡¡of¡¡the¡¡gastric¡¡juice£»¡¡which£»¡¡while¡¡unable¡¡to¡¡act¡¡upon¡¡the¡¡living¡¡tissue£»¡¡continued¡¡its¡¡action¡¡chemically¡¡after¡¡death£»¡¡thus¡¡digesting¡¡the¡¡walls¡¡of¡¡the¡¡stomach¡¡in¡¡which¡¡it¡¡had¡¡been¡¡formed¡£¡¡¡¡And£»¡¡as¡¡usual¡¡with¡¡his¡¡observations£»¡¡be¡¡turned¡¡this¡¡discovery¡¡to¡¡practical¡¡use¡¡in¡¡accounting¡¡for¡¡certain¡¡phenomena¡¡of¡¡digestion¡£¡¡¡¡The¡¡following¡¡account¡¡of¡¡the¡¡stomach¡¡being¡¡digested¡¡after¡¡death¡¡was¡¡written¡¡by¡¡Hunter¡¡at¡¡the¡¡desire¡¡of¡¡Sir¡¡John¡¡Pringle£»¡¡when¡¡he¡¡was¡¡president¡¡of¡¡the¡¡Royal¡¡Society£»¡¡and¡¡the¡¡circumstance¡¡which¡¡led¡¡to¡¡this¡¡is¡¡as¡¡follows£º¡¡¡¨I¡¡was¡¡opening£»¡¡in¡¡his¡¡presence£»¡¡the¡¡body¡¡of¡¡a¡¡patient¡¡of¡¡his¡¡own£»¡¡where¡¡the¡¡stomach¡¡was¡¡in¡¡part¡¡dissolved£»¡¡which¡¡appeared¡¡to¡¡him¡¡very¡¡unaccountable£»¡¡as¡¡there¡¡had¡¡been¡¡no¡¡previous¡¡symptom¡¡that¡¡could¡¡have¡¡led¡¡him¡¡to¡¡suspect¡¡any¡¡disease¡¡in¡¡the¡¡stomach¡£¡¡I¡¡took¡¡that¡¡opportunity¡¡of¡¡giving¡¡him¡¡my¡¡ideas¡¡respecting¡¡it£»¡¡and¡¡told¡¡him¡¡that¡¡I¡¡had¡¡long¡¡been¡¡making¡¡experiments¡¡on¡¡digestion£»¡¡and¡¡considered¡¡this¡¡as¡¡one¡¡of¡¡the¡¡facts¡¡which¡¡proved¡¡a¡¡converting¡¡power¡¡in¡¡the¡¡gastric¡¡juice¡£¡¡¡£¡¡¡£¡¡¡£¡¡There¡¡are¡¡a¡¡great¡¡many¡¡powers¡¡in¡¡nature¡¡which¡¡the¡¡living¡¡principle¡¡does¡¡not¡¡enable¡¡the¡¡animal¡¡matter£»¡¡with¡¡which¡¡it¡¡is¡¡combined£»¡¡to¡¡resistviz¡££»¡¡the¡¡mechanical¡¡and¡¡most¡¡of¡¡the¡¡strongest¡¡chemical¡¡solvents¡£¡¡It¡¡renders¡¡it£»¡¡however£»¡¡capable¡¡of¡¡resisting¡¡the¡¡powers¡¡of¡¡fermentation£»¡¡digestion£»¡¡and¡¡perhaps¡¡several¡¡others£»¡¡which¡¡are¡¡well¡¡known¡¡to¡¡act¡¡on¡¡the¡¡same¡¡matter¡¡when¡¡deprived¡¡of¡¡the¡¡living¡¡principle¡¡and¡¡entirely¡¡to¡¡decompose¡¡it¡£¡¡¡¡¡¨

Hunter¡¡concludes¡¡his¡¡paper¡¡with¡¡the¡¡following¡¡paragraph£º¡¡¡¨These¡¡appearances¡¡throw¡¡considerable¡¡light¡¡on¡¡the¡¡principle¡¡of¡¡digestion£»¡¡and¡¡show¡¡that¡¡it¡¡is¡¡neither¡¡a¡¡mechanical¡¡power£»¡¡nor¡¡contractions¡¡of¡¡the¡¡stomach£»¡¡nor¡¡heat£»¡¡but¡¡something¡¡secreted¡¡in¡¡the¡¡coats¡¡of¡¡the¡¡stomach£»¡¡and¡¡thrown¡¡into¡¡its¡¡cavity£»¡¡which¡¡there¡¡animalizes¡¡the¡¡food¡¡or¡¡assimilates¡¡it¡¡to¡¡the¡¡nature¡¡of¡¡the¡¡blood¡£¡¡The¡¡power¡¡of¡¡this¡¡juice¡¡is¡¡confined¡¡or¡¡limited¡¡to¡¡certain¡¡substances£»¡¡especially¡¡of¡¡the¡¡vegetable¡¡and¡¡animal¡¡kingdoms£»¡¡and¡¡although¡¡this¡¡menstruum¡¡is¡¡capable¡¡of¡¡acting¡¡independently¡¡of¡¡the¡¡stomach£»¡¡yet¡¡it¡¡is¡¡indebted¡¡to¡¡that¡¡viscus¡¡for¡¡its¡¡continuance¡££§5£§


THE¡¡FUNCTION¡¡OF¡¡RESPIRATION

It¡¡is¡¡a¡¡curious¡¡commentary¡¡on¡¡the¡¡crude¡¡notions¡¡of¡¡mechanics¡¡of¡¡previous¡¡generations¡¡that¡¡it¡¡should¡¡have¡¡been¡¡necessary¡¡to¡¡prove¡¡by¡¡experiment¡¡that¡¡the¡¡thin£»¡¡almost¡¡membranous¡¡stomach¡¡of¡¡a¡¡mammal¡¡has¡¡not¡¡the¡¡power¡¡to¡¡pulverize£»¡¡by¡¡mere¡¡attrition£»¡¡the¡¡foods¡¡that¡¡are¡¡taken¡¡into¡¡it¡£¡¡¡¡However£»¡¡the¡¡proof¡¡was¡¡now¡¡for¡¡the¡¡first¡¡time¡¡forthcoming£»¡¡and¡¡the¡¡question¡¡of¡¡the¡¡general¡¡character¡¡of¡¡the¡¡function¡¡of¡¡digestion¡¡was¡¡forever¡¡set¡¡at¡¡rest¡£¡¡Almost¡¡simultaneously¡¡with¡¡this¡¡great¡¡advance£»¡¡corresponding¡¡progress¡¡was¡¡made¡¡in¡¡an¡¡allied¡¡field£º¡¡¡¡the¡¡mysteries¡¡of¡¡respiration¡¡were¡¡at¡¡last¡¡cleared¡¡up£»¡¡thanks¡¡to¡¡the¡¡new¡¡knowledge¡¡of¡¡chemistry¡£¡¡The¡¡solution¡¡of¡¡the¡¡problem¡¡followed¡¡almost¡¡as¡¡a¡¡matter¡¡of¡¡course¡¡upon¡¡the¡¡advances¡¡of¡¡that¡¡science¡¡in¡¡the¡¡latter¡¡part¡¡of¡¡the¡¡century¡£¡¡Hitherto¡¡no¡¡one¡¡since¡¡Mayow£»¡¡of¡¡the¡¡previous¡¡century£»¡¡whose¡¡flash¡¡of¡¡insight¡¡had¡¡been¡¡strangely¡¡overlooked¡¡and¡¡forgotten£»¡¡had¡¡even¡¡vaguely¡¡surmised¡¡the¡¡true¡¡function¡¡of¡¡the¡¡lungs¡£¡¡The¡¡great¡¡Boerhaave¡¡had¡¡supposed¡¡that¡¡respiration¡¡is¡¡chiefly¡¡important¡¡as¡¡an¡¡aid¡¡to¡¡the¡¡circulation¡¡of¡¡the¡¡blood£»¡¡his¡¡great¡¡pupil£»¡¡Haller£»¡¡had¡¡believed¡¡to¡¡the¡¡day¡¡of¡¡his¡¡death¡¡in¡¡1777¡¡that¡¡the¡¡main¡¡purpose¡¡of¡¡the¡¡function¡¡is¡¡to¡¡form¡¡the¡¡voice¡£¡¡No¡¡genius¡¡could¡¡hope¡¡to¡¡fathom¡¡the¡¡mystery¡¡of¡¡the¡¡lungs¡¡so¡¡long¡¡as¡¡air¡¡was¡¡supposed¡¡to¡¡be¡¡a¡¡simple¡¡element£»¡¡serving¡¡a¡¡mere¡¡mechanical¡¡purpose¡¡in¡¡the¡¡economy¡¡of¡¡the¡¡earth¡£

But¡¡the¡¡discovery¡¡of¡¡oxygen¡¡gave¡¡the¡¡clew£»¡¡and¡¡very¡¡soon¡¡all¡¡the¡¡chemists¡¡were¡¡testing¡¡the¡¡air¡¡that¡¡came¡¡from¡¡the¡¡lungsDr¡£¡¡Priestley£»¡¡as¡¡usual£»¡¡being¡¡in¡¡the¡¡van¡£¡¡¡¡His¡¡initial¡¡experiments¡¡were¡¡made¡¡in¡¡1777£»¡¡and¡¡from¡¡the¡¡outset¡¡the¡¡problem¡¡was¡¡as¡¡good¡¡as¡¡solved¡£¡¡Other¡¡experimenters¡¡confirmed¡¡his¡¡results¡¡in¡¡all¡¡their¡¡essentialsnotably¡¡Scheele¡¡and¡¡Lavoisier¡¡and¡¡Spallanzani¡¡and¡¡Davy¡£¡¡¡¡It¡¡was¡¡clearly¡¡established¡¡that¡¡there¡¡is¡¡chemical¡¡action¡¡in¡¡the¡¡contact¡¡of¡¡the¡¡air¡¡with¡¡the¡¡tissue¡¡of¡¡the¡¡lungs£»¡¡that¡¡some¡¡of¡¡the¡¡oxygen¡¡of¡¡the¡¡air¡¡disappears£»¡¡and¡¡that¡¡carbonic¡­acid¡¡gas¡¡is¡¡added¡¡to¡¡the¡¡inspired¡¡air¡£¡¡¡¡It¡¡was¡¡shown£»¡¡too£»¡¡that¡¡the¡¡blood£»¡¡having¡¡come¡¡in¡¡contact¡¡with¡¡the¡¡air£»¡¡is¡¡changed¡¡from¡¡black¡¡to¡¡red¡¡in¡¡color¡£¡¡These¡¡essentials¡¡were¡¡not¡¡in¡¡dispute¡¡from¡¡the¡¡first¡£¡¡¡¡But¡¡as¡¡to¡¡just¡¡what¡¡chemical¡¡changes¡¡caused¡¡these¡¡results¡¡was¡¡the¡¡subject¡¡of¡¡controversy¡£¡¡Whether£»¡¡for¡¡example£»¡¡oxygen¡¡is¡¡actually¡¡absorbed¡¡into¡¡the¡¡blood£»¡¡or¡¡whether¡¡it¡¡merely¡¡unites¡¡with¡¡carbon¡¡given¡¡off¡¡from¡¡the¡¡blood£»¡¡was¡¡long¡¡in¡¡dispute¡£

Each¡¡of¡¡the¡¡main¡¡disputants¡¡was¡¡biased¡¡by¡¡his¡¡own¡¡particular¡¡views¡¡as¡¡to¡¡the¡¡moot¡¡points¡¡of¡¡chemistry¡£¡¡¡¡Lavoisier£»¡¡for¡¡example£»¡¡believed¡¡oxygen¡¡gas¡¡to¡¡be¡¡composed¡¡of¡¡a¡¡metal¡¡oxygen¡¡combined¡¡with¡¡the¡¡alleged¡¡element¡¡heat£»¡¡Dr¡£¡¡Priestley¡¡thought¡¡it¡¡a¡¡co

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