42 Optics & Photonics News ■ October2001

The Fren ch scien tist and ph i l o s o-ph er René De s c a rtes (1596-1650)is cel ebra ted by historians of s c i-

en ce for his con tri buti ons to the discretem a t h em a tical scien ces (analytic geom etry,sine law of ref racti on , etc . ) . In his day,h owever, he was ren own ed (and, in som equ a rters , revi l ed) for the startling thesisthat all things , i n cluding living cre a -tu re s ,a re machines (autom a t a ) . De s c a rte s( F i g. 1) was not the first to attem pt tom odel bi o l ogical ph en om ena on mech a n-ical devi ces (Johannes Kep l er had tre a tedthe living eye as far as the su rf ace of t h eretina as an inanimate optical instru-m en t ) , but it was De s c a rtes who pion eeredthe idea that living things are nothingm ore than mechanical devi ce s , a s s em bl edo ut of l i feless parti cles that co ll a bora te toprodu ce moti on in the wh o l e .

BRIAN S.BAIGRIE

c a rtes con ten ded that they requ i re theconstant atten ti on of s ome ex tern a lm over: l i ke the mainspring of a watch ,l iv-ing things need to be wound up by som eex ternal agen t . Po s tu l a ting that God intro-du ced a fixed qu a n ti ty of m o ti on into thecosmos at the time of c re a ti on , De s c a rte sex p l a i n ed the ph en om en on of l i fe in term sof the red i s tri buti on of m o ti on du ring thecountless co ll i s i ons bet ween minute parti-cles of m a t ter. He argued that God con-s erved that fixed qu a n ti ty of m o ti on , u l ti-m a tely making po s s i ble life .

De s c a rte s’ i n trodu cti on of the con s erv-ing influ en ce of G od to explain the activi-ties of or ganisms was unattractive to ei gh-teenth cen tu ry phys i o l ogi s t s , who were in-c re a s i n gly seeking to frame purely natu ra-l i s tic ex p l a n a ti ons for bi o l ogical ph en om-en a . P hys i o l ogists were also adverse to

The insisten ce that there is no line to bed rawn bet ween living and non l ivi n gt h i n gs was the most revo luti on a ry fe a tu reof De s c a rte s’ m ech a n i s tic phys i o l ogy. Ith ad long been assu m ed that living thingswere po s s e s s ed of a vital en ti ty (sep a ra tef rom their parts) that animated them andex p l a i n ed their ch a racteri s tic activi ti e s —an idea that persists tod ay in su ch familiarex pre s s i ons as “s c i en tists wi ll som ed ay cre-a te life in the test tu be” and “he lost hisl i fe .” Al t h o u gh natu re cl e a rly is not sti lland lifel e s s , for De s c a rtes the movem en tand growth that we intu i tively assoc i a tewith the pre s en ce of l i fe was just a me-chanical ef fect , one that differed in no sig-nificant way from the prop u l s i on of w a tert h ro u gh pipes by a pump (Fig. 2 ) .

Al t h o u gh living things seem to be ca-p a ble of s el f - i n i ti a ted movem en t , De s -

Bioelectricity and theOrigins of Physiology

Original engraving:L'Homme de René Descartes.

nals an el ectrical ch a r ge by the diver gen ceof s traws or met a llic ri bbon s . An o t h erpo s s i bi l i ty was that the frog mu s cles re-t a i n ed some sort of i n n a te animal el ectri c-i ty even after the frog had ex p i red .

G a lvani em braced this latter vi ew. Con-ceiving a living cre a tu re as a fleshy kind ofLeyden ja r, he argued that the moti on wasc a u s ed by a vital fluid he term ed animalel ectri c i ty. Al t h o u gh Galvani con ceivedthis fluid as having an el ectric natu re , h i svi ew was part of a long-standing trad i ti on ,that iden ti f i ed life with the breath and thebl ood , and would influ en ce Ma ry Shell ey ’sFra n ken s tei n. In Galva n i ’s new model ofthe basic stru ctu re of l iving matter, t h en erve and mu s cle con s ti tuted the innerand outer ch a r ged su rf aces of the ja r.Wh en the outer su rf ace of the mu s cl e s —l i ke the outer su rf ace of the Leyden ja r —received an el ectrical ch a r ge , the nerve andi n n er muscular su rf ace became oppo s i tely

ch a r ged ,l e ading to muscular con tracti on .G a lva n i ’s paper received a great deal of

c ri tical discussion , as one might ex pect ofa new con cepti on of the or ganism as hav-ing an el ectrical natu re . It was circ u l a teda m ong fell ow scien ti s t s , i n clu d i n gAl e s s a n d ro Volta (1745-1827), who re-pe a ted his ex peri m en t s . A ch emist andphysicist by trade , Volta was skepti c a la bo ut the noti on of animal el ectri c i ty. Hege a red his ex peri m ents tow a rd Galva n i ’sm odel of a Leyden ja r. Con cen tra ting them et a llic probes on the nerves on ly, t h ereby

gen era tors (Fig. 3 ) , t h ey began to won dera bo ut the rel a ti onship bet ween the phys i-o l ogical ef fect of its disch a r ge and that ofs h ocks given of f by these marine animals.Af ter all , the ex p l o s ive power of the dis-ch a r ge from a su i t a bly prep a red Leyden ja rwas legen d a ry—it could kill bi rds ands m a ll animals, and even , in a famousdem on s tra ti on before the King of Fra n ce ,t h row an en ti re com p a ny of 180 soldierss i mu l t a n eo u s ly into the air. It was there-fore to be ex pected that scien tists wo u l dcome to see the Leyden jar as a model foror ganic ph en om en a .

In a rem a rk a ble series of ex peri m en t sthat com m en ced around 1780 or so, G a l-vani found that dissected frog’s legst wi tch ed as though in spasm or convu l-s i on on con t act with a spark from an el ec-tric machine (Fig. 4 ) . What is more , h efound that a metal scalpel caused the frog’sl egs to twi tch if the machine was tu rn edon , even if the spark didnot actu a lly make con t act .If an el ectrical sparkc a u s ed this mu s cle twi tch-i n g, G a lvani reckon ed thathe could con f i rm the hy-po t h e s i s , adva n ced in 1749by Ben jamin Fra n k l i n( 1 7 0 6 - 1 7 9 0 ) , that ligh t-ning was a form of el ec-tri c i ty (as oppo s ed to re-ceived op i n i on wh i ch hel dthat ligh tning was due toex p l oding ga s e s ) . To te s tFra n k l i n’s hypo t h e s i s ,G a l-vani hung the legs of f rogsby their nerves from bra s sh ooks against an iron lat-ti cework . The lower tip ofthe su s pen ded mem berwas con n ected to agro u n ded wi re . He found that the legst wi tch ed wh en thu n derclouds appe a redbut they also twi tch ed wh en there were not hu n ders torm s . He noti ced that twi tch i n gcould be seen even wh en the we a t h er wasp l e a s a n t . The twi tching occ u rred ,G a lva n id i s covered , wh en ever the mu s cles camei n to con t act with two different metals atthe same ti m e .

Si n ce the same twi tching was ob s ervedwh en the spec i m en was moved indoors ,G a lvani ru l ed out atm o s ph eric con d i ti on sas the root of the muscular con tracti on s .Perhaps the metals were the cause of t h et wi tching—the twi tching legs indicati n gan el ectric ch a r ge gen era ted from out s i dein the same way that an el ectro s cope sig-

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De s c a rte s’ portrait of the cen tral nervo u ss ys tem as a set of hyd raulic pipe s , the ch i efp u rpose of wh i ch was to com mu n i c a tes ti mu lus to the brain and carry fluid backto the mu s cl e s , causing a con tracti on .These misgivi n gs aside , t h ey were held int h ra ll by De s c a rte s’ proj ect of a purely me-chanical phys i o l ogy.

The re s e a rch program adva n ced byDe s c a rtes received an en ormous boo s twith the rise of s tudies of el ectri c i ty du r-ing the late ei gh teenth cen tu ry. Th e s es tudies open ed the door to the po s s i bi l i tyof l oc a ting the source of an or ga n i s m’s ac-tivi ty within the or ganism itsel f — f rommuscular con tracti on to the neu ral activi-ty of the human bra i n , el ectri c i ty wi t h i nthe or ganism could be ex p l oi ted to ex p l a i nits activi ti e s , t h ereby ren dering divine in-terven ti on com p l etely unnece s s a ry.

The scien tist who first attem pted tofuse the stu dy of el ectri c i ty with the sci-en ce of phys i o l ogy was Lu i gi Galva n i( 1 7 3 7 - 1 7 9 8 ) , for wh om the process ofel ectri c a lly plating steel with zinc (ga lva-nizing) is named . An anatomist and phys i-cian at the Un ivers i ty of Bo l ogn a , t h eworl d ’s oldest con ti nuing univers i ty, in hisCo m m en t a ry on the Fo rces of E l e ctri ci ty inMu scular Moti o n ( 1 7 9 1 ) , G a lvani dem on-s tra ted that mu s cle re s ponse depends onthe del ivery of el ectri c i ty to the nervet h ro u gh a con du ctor.

From very early ti m e s , it was knownthat some marine animals (e.g. , el ectri c a leels) are capable of giving shock s . Af ters c i en tists discovered in 1745 how to gen er-a te and acc u mu l a te static el ectrical ch a r ge sin Leyden ja rs or ro t a ting static el ectri c i ty

Figure 2. Action of the nerves.(Original engrav-ing: L'Homme de René Descartes.)

F i g u re 1. Po rtrait of René Descart e s . (C o u rtesy A I PEmilio Segrè Visual Archives.)

taking the mu s cles out of the pictu re , h esu cceeded in cre a ting an ex peri m en t a la rra n gem ent that no lon ger functi on edl i ke a Leyden ja r. This rede s i gn ed app a ra-tu s , he fo u n d , produ ced the same re su l t s .

Volta was stru ck by the fact that el ec-tri c i ty was produ ced on ly if t wo differen tm etals were used . He tri ed placing a pieceof ti n foil and a silver coin in his mout h ,one on top of the ton g u e , the other to u ch-ing his ton g u e’s lower su rf ace . Wh en thefoil was pre s s ed to the coi n , a sour tastewas produ ced in his mout h , wh i ch Vo l t ai n terpreted as indicating the pre s en ce ofan el ectrical disch a r ge . The taste lasted asl ong as the tin and silver were in con t actwith each other, s h owing that the flow ofel ectri c i ty from one to the other was con-ti nu o u s . A silver spoon was su b s ti tuted forthe coin and a copper wi re for the ti n foi l ,with the same re su l t . The met a l s , he con-

clu ded , were not just con du ctors but wereactu a lly re s pon s i ble for the produ cti on ofel ectri c i ty. The frog’s legs had ex h i bi ted notanimal el ectri c i ty but met a llic el ectri c i ty.

Con ti nuing his ex peri m en t s , Volta re-a l i zed that el ectrical forces were gen era tednot on ly wh en two dissimilar met a l sto u ch ed but also wh en a metal to u ch edcertain kinds of f lu i d . Wh en he placeddisks of s i lver, ti n , or zinc on moist cl o t h ,cl ay, or wood and then sep a ra ted themand bro u ght them to the el ectrom eter, an ega tive el ectri f i c a ti on re su l ted . Hes h owed furt h er that improved re sults wereprodu ced wh en a circuit was form ed byt wo different metals sep a ra ted by a moi s tel em en t , and that their ef fectiveness wasi n c re a s ed wh en su ch com bi n a ti ons of

m etals and moist el em ent were stacked ina repe a ting pattern .

In this way, Volta su cceeded in bu i l d i n ghis famous co lumn or pile of el ectric gen-era ting el em ents (Fig. 5 ) , the basis of a llm odern wet - cell batteri e s . He ex peri m en t-ed with many soluti on s ,f i n a lly settling onbri n e . He found that if he con s tru ctedpiles of dissimilar metal disks, s a n dwi ch-ing pieces of c a rd boa rd - s oa ked brine inbet ween them , he had a very ef fective setof b a t tery cells (each sandwi ch form i n gone cell ) . The inven ti on of the el ectri c a lb a t tery was announced in 1800, with Vo l t adem on s tra ting its acti on the fo ll owi n gyear in Pa ri s .

Vo l t a’s ex peri m ents were immed i a telyrep l i c a ted by scien tists on both sides of t h eAt l a n ti c , who recogn i zed that a source ofcon s t a n t - c u rrent el ectri c i ty would ulti-m a tely tra n s form establ i s h ed disciplines inw ays that had been heretofore unimagi n-a bl e . The discipline that re a ped the gre a t-est immed i a te ben efit from Vo l t a’s batterywas ch em i s try, wh i ch now po s s e s s ed apowerful tool for tracking down new el e-m ents and understanding the natu re ofch emical bon d i n g.

The most ambi tious ex peri m en ter wi t hthe new tech n o l ogy was Hu m ph ry Dav y( 1 7 7 8 - 1 8 2 9 ) , who persu aded himsel f t h a tthe voltaic cell produ ced el ectri c i tyt h ro u gh ch emical re acti on . He con j ec-tu red that the reverse might also be tru e —that the app l i c a ti on of el ectri c i ty to com-pounds and mixtu res might produ cech emical re acti on s . With an ex tra stron gb a t tery, in 1807 Davy ex tracted po t a s s iu mf rom a lump of d a m pen ed potash and aweek later sod ium from caustic soda (nowk n own as sod ium hyd rox i de ) .

The en ormous su ccess that ch em i s t sen j oyed with Vo l t a’s battery on ly rei n-forced Vo l t a’s claim that Galva n i ’s inter-pret a ti on of his ex peri m ents had beenm i sg u i ded . Even so, G a lva n i ’s underlyi n gconvi cti on that el ectrical ph en om ena arei nvo lved in life processes was hardlyto u ch ed by Vo l t a’s cri ti c i s m . The on ly is-sue for the scien ce of phys i o l ogy in thecoming ye a rs was the natu re of this in-vo lvem en t — wh et h er it would be ex-pre s s ed (fo ll owing De s c a rtes) in purelym echanical terms or would lend creden ceto Galva n i ’s convi cti on that living thingsa re animated by animal el ectri c i ty.

The stu dy of bi oel ectri c i ty waned inthe qu a rter cen tu ry fo ll owing Vo l t a’s his-toric announcem en t , not because the in-terest of phys i o l ogists had been dampen ed

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44 Optics & Photonics News ■ October2001

F i g u re 5. Volta's pile. One version fe a t u red a pileof silver and zinc disks, separated by paper or clothseparators soaked in brine; another fe a t u red a ringof cups filled with brine and connected by alternatestrips of zinc and silver joined by metallic jumpers.(S o u r c e : 1800s photo image.)

Figure 4. Galvani’s experiment. (Source:18th Cen -tury engraving of Galvani’s laboratory.)

F i g u re 3. The Leyden jar, the first electrical con-d e n s o r. In its original fo r m , the Leyden jar was aglass jar or bottle capable of storing a static electriccharge that could be re l e a s e d ,when gro u n d e d ,w i t he x p l o s i ve effe c t . (Photo Cre d i t :P hysics Museum, U n i -v e rsity of Coimbra , Po rt u g a l. )

by Vo l t a’s cri ti que of G a lvani but bec a u s et h ey found that they could make no usef u lh e adw ay on the practical probl em ofm e a su ring the el ectrical currents though tto be gen era ted in the nervous and mu s c u-lar cell s — c u rrents that were so weak thatt h ey could not be detected with ava i l a bl eel ectro s cope s . Th ere a f ter the stu dy of bi o-el ectri c i ty was revived by a new sch ool ofphys i o l ogi s t s . The cen tral figure in thiss ch ool was the Swiss scien tist Emil Hei n-ri ch Du Boi s - Reym ond (1818-1896), pro-fe s s or of phys i o l ogy in Berl i n . Thanks tothe inven ti on of the ga lva n om eter twodec ades earl i er, in 1848-1849 Du Boi s -Reym ond was able to detect what he call edacti on current in the frog's nerve and wassu b s equ en t ly able to dem on s tra te that thisph en om en on also occ u rs in stri a ted mu s-cle and is the pri m a ry cause of mu s c u l a rcon tracti on . His con tri buti on s , p u bl i s h edin his boo k , Re se a rches on Animal Electri c -i ty ( 1 8 4 8 ) ,a re the fo u n d a ti on for the fiel dof bi oel ectri c i ty.

Du Boi s - Reym on d ’s re s e a rch was dic-t a ted by the basic principle of m ech a n i c a lex p l a n a ti on that in a living thing no force sh ave any ef fect other than the familiarphys i och emical ones—a principle that hass i n ce dom i n a ted the scien ce of phys i o l ogy.In the wake of his ach i evem en t s , n i n e-teenth cen tu ry phys i o l ogists were able torep l ace De s c a rte s’ quaint portrait ofn erves as water pipes with the modernvi ew that inform a ti on within the nervo u ss ys tem is carri ed by el ectri c i ty gen era tedd i rect ly by or ganic ti s su e .

In historical recon s tru cti on s , i f the fo-cus is on the place of el ectri c i ty in the con-s tru cti on of m odern phys i o l ogy, G a lva n iwi ll su rely be gra n ted a prom i n ent po s i-ti on , s i n ce it was he who ch a m p i on ed thei dea that el ectri c i ty is cen tra lly invo lved inthe activi ties of l iving things . For Galva n i ,h owever, animal el ectri c i ty was a vital flu-id that was similar to ord i n a ry static el ec-tri c i ty but a property of l iving thingsa l on e . If our em ph a s i s , i n s te ad , is on them ech a n i z a ti on of phys i o l ogy, it is cl e a rthat el ectri c i ty became a cen tral part ofphys i o l ogy on ly wh en the new gen era ti onof phys i o l ogists found a way to fra m ep u rely mechanical interpret a ti ons for theacti on of el ectri c i ty within living things .The mechanisms that De s c a rtes adva n cedto explain the activi ties of l iving thingsm ay be quaint by pre s ent standard s , butt h ey are cl o s er in spirit to the mech a n i s m spo s tu l a ted by modern phys i o l ogists thanwe may at first be incl i n ed to bel i eve .

Further reading1. A.Chapuis and E.Droz, Automata:A Historical and

Technological Study.Translated by Alec Reid,Neuchatel:Editions du Griffon (1958).

2. R.Descartes, L'Homme de René Descartes,Paris:Charles Angot (1664).

3. T. S.Hall,History of General Physiology [first pub-lished as Ideas of Life and Matter] Chicago:ChicagoUniversity Press (1969).

4. J.Jaynes,"The Problem of Animate Motion in theSeventeenth Century," J.of the History of Ideas 31,219-34 (1970).

5. J.Loeb , The Mechanistic Conception of Life. Chica-go:University of Chicago Press (1912).

6. D. J.S.Price, "Automata and the Origins of Mecha-nism and the Mechanistic Philosophy," Technologyand Culture 5, 9-42 (1964).

7. J. F. Scott, The Scientific Work of René Descartes(1596-1650).NewYork:Taylor and Francis (1952).

Brian S.Baigrie is associate professor at the Institutefor History and Philosophy of Science and Technology,U n i versity of To ro n t o, To ro n t o, C a n a d a . He can bereached by e-mail at baigrie@attcanada.net.

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