liana Lowy

Ludwik Fleck on the social construction ofmedical knowledge

Abstract The subject of the development and transmission of medicalknowledge has remained, until recently, relatively little studiedby medical sociologists. But as early as the 1930s the pioneeringstudies of Ludwik Fleck, a physician and historian of science,dealt with the evolution of medical knowledge and the genesisof medical facts. Starting with a reflection on his own experienceas clinical bacteriologist and immunologist. Fleck developedhighly original views on subjects such as the influence ofpatterns of specialization of physicians on the medicalknowledge they produced, the impact of popular models ofdisease on expert ones, and the importance of the circulation ofideas between distinct, and - according to Fleck -incommensurable 'thought collectives' (medical scientists,general practitioners and patients) for the development ofinnovations in medicine. The aim of this article is to analyzeFleck's vision of medicine and to select among his ideas thosewhich may be of interest for sociologists of medicine today.

Introduction

The sociology of health and illness is concerned with a wide range ofsubjects dealing with the ways society takes care of its sickmembers. One subject is, however, often missing from the ever-growing list of topics studied by sociologists: the impact of societyon the development of present medical knowledge. Until recently,sociologists dealing with medical subjects have usually separatedissues concerning the behaviour of physicians and their knowledge.Although they have examined the infiuence of society on thedevelopment of medical knowledge in primitive and folk medicineand in the past, they have often made an absolute distinctionbetween this 'non-scientific medical knowledge' and modem scientific

Sociology of Health & Illness Vol.10 No. 2 1988 ISSN0141-9889

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medicine. Modern medical knowledge has been viewed in manyworks of medical sociology as homogeneous, culture-independentand founded on objective observation and experimentation (King1962: 93; Freeman, Levine and Reeder 1972: x-xi; Albrecht andHiggins 1979: 7-10). The hesitations of medical sociologists inapplying their usual methods of investigation to the study of theformation and evolution of present medical knowledge refiectedperhaps their lack of competence on medical topics on the onehand, and their professional strategy of aspiring to recognition byphysicians on the other (Kendall and Reader 1972: 1-21; Strong1984).

In the last ten years, however, several studies have dealt with theinfluence of society on the evolution of medical science. The recentdevelopment of social studies of science, and increased interest inthe social construction of scientific knowledge (Bloor 1976; Knorr,Krohn and Whitley 1981, Knorr and Mulkay 1982) have inspiredstudies dealing with the social construction of medical knowledge(e.g. Wright and Treacher 1982; Figlio 1982; Gabbay 1982;Amstrong 1983. For a review see Bury 1986; Nicolson andMcLaughin 1987). Another recent evolution has been the formationof a new specialty: the philosophy of medicine. This deals, amongother things, with the specificity of medical knowledge and itsrelationship to biology and the natural sciences in general (Gorvitzand Maclntyre 1976; MauU 1981, Schaffner 1986; Caplan 1986). Thedevelopments of the last years cannot, however, in my opinion,justify the idea that the sociology of biomedical research alreadyexists. Rather, I would agree with Renee Fox who recently affirmedthat: 'For many years, I have been amazed at the virtual absence offirst-hand sociology of medical studies' (Fox 1985). Philosophershave attempted to define the overall conceptual framework ofmedicine and have not studied the impact of societal factors on theevolution of medical knowledge in concrete cases. Sociologists whohave approached this subject have often been more interested in therelationships between social models of health and illness and theprofessional strategies of doctors than in the development ofmedical knowledge itself.

Ludwik Fleck's philosophy and sociology of science

The problem of the impact of society on the genesis of medicalknowledge was addressed as early as the 1920s and 30s, when a

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highly original attempt to study it was made by a Polish-Jewishphysician, Ludwik Fleck (1896-1961). Fleck, a bacteriologist andimmunologist, combined strong philosophical and sociologicalinterests with medical training and long practice in a clinicallaboratory. For many years his works remained practically unnoticedby historians, philosophers and sociologists of science. They wererediscovered after the publication of The Structure of ScientificRevolutions., where in the introduction Kuhn cites Fleck's Genesisand Development of a Scientific Fact (Fleck 1935a) among the worksthat influenced his own thought (Kuhn 1962: viii-ix).

In his epistemological works Fleck developed the notion thatscientific knowledge is constructed. For him, alleged scientific 'facts'do not exist 'out there' in nature waiting to be discovered byobjective and interchangeable observers. Rather, they emerge asthe final result of a social process: the 'genesis and development of ascientific fact'. The observer's training, his preconceived ideas, andhis anticipations play a substantial role. Moreover, for Fleckscientific facts are constructed by distinct 'thought collectives', eachcomposed of individuals who share a specific 'thought style'.Different and equally well-founded 'thought styles' can co-exist in agiven domain, not only diachronically, in distinct historical periods,but also synchronically and within the same cultural universe.Fleck's approach was therefore at least partially relativist: not onlyis scientific knowledge constructed, but speaking of truth andfalsehood is meaningful only within a specific thought collective andwith respect to a given thought style. He was not, however, acomplete relativist (although his work is sometimes represented assuch). Fleck did not believe that observations are radically theory-laden and he considered science as capable of cumulative improve-ment (Fleck 1929; 1935c; Toulmin 1986).

Today the majority of historians and philosophers of scienceagree that in science theory and observation are interdependent.This was certainly not the case in the 1920s and 30s, whenepistemology and the philosophy of science in many countries(including Poland) was dominated by positivism. But not allhistorians and philosophers of science adhered to positivisticapproach. A conventionalist approach to the philosophy of science,stressing the conventional nature of all scientific knowledge, wasdeveloped, probably as a response to the crisis in physics, at thebeginning of the 20th century (H. Poincare, P. Duhem) and developedby historians of science (Metzger, Koyre). The conventionalist pointof view also had adherents among Polish philosophers of science in

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the 1920s and 30s (K. Adjukiewicz, E. Poznanski, A. Wundheiler).Historians of culture, art and ideas of that period readily viewedscience as but one aspect of the general creativity of human beings,and as such dependent on the wider socio-cultural context (Lovejoy1936; Panofsky 1940). Some historians of science (H. Metzger, F.Enriques) shared this view and stressed the crucial importance ofstudying the science of past periods in its philosophical, cultural andsocial contexts. According to Metzger the historian of scienceshould 'make himself the contemporary of the scientists he isstudying' (Metzger 1933). Similarly, historians of medicine workingin the 1920s in the influential Institute for the History of Medicine inLeipzig (H. Sigerist and his students, among them O. Temkin,E. Ackerknecht, and also the Polish historian of medicineT. Bilikiewicz) developed a similar approach. Influenced byGerman historicism, they claimed that the medicine of a givenhistorical period should be studied only from the point of view of theperiod in which it was developed and that one should avoid thetemptation of making modem judgments on past science (Temkin1977).

If conventionism in philosophy and historical relativism in thehistory of medicine existed already (albeit as minority trends) in the1920s and 30s, and if representatives of these trends were present inPoland in the period during which Fleck published his majorepistemological studies, why did his works remain practicallyunknown for such a long time?

In the 1920s and 30s the history and philosophy of medicine wereestabhshed academic disciplines in Poland. In all probabiUty, Fleckaspired therefore to be recognized by the historians and philosophersof medicine of his country. However, even the historians ofmedicine who acknowledged that past medical knowledge wasstrongly influenced by the cultural context in which it had beendeveloped were not ready to accept Fleck's radical claim thatmodem, 'scientific' medicine is as dependent on social and culturalfactors as the medicine of the past (Bilikiewicz 1939). As to thereason for the ignoring of Fleck's studies by Polish philosophers ofscience, several answers have been proposed: a) Fleck's approachwas not new when considered against the background of Polishphilosophy in the thirties: philosophers affected by the conventionalisttradition were in agreement with the conventionalist components ofFleck's philosophy, but felt that they had little to learn from him,while those who rejected conventionalism found his views uncon-vincing (Giedymn 1986); b) Polish philosophy of this period

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developed a very high logical-methodological standard for what wasconsidered worthy of discussion in epistemology; Fleck's writingscould not satisfy this because his style of thought was incompatiblewith the dominant style of the Warsaw-Lwow philosophical school(Wolniewicz 1986).

This last point merits further discussion. Why was Fleck's style sodifferent from the one which dominated Polish philosophy ofscience in his time? The reason, I suggest, is that it was developedindependently of this philosophy. Indeed, as I have arguedelsewhere (Lowy 1986), Fleck's epistemology has its roots not in hisphilosophical training but rather in his scientific and medicalpractice. Taking his own clinical laboratory practice as a startingpoint for his epistemological reflections. Fleck did not ask whatscience must be, but attempted to investigate what science actually isand how historial processes and social institutions are related to theemergence of scientific 'facts'. In doing so Fleck broke radically withthe idea, predominant in the philosophy of science in the 1920s and30s, that philosophers are required to 'justify' science and to provideit with intellectual 'foundations'; instead. Fleck proposed anempirical research program for epistemology (Toulmin 1986).

Fleck's preoccupation with the ways science in fact operatesalienated him from the community of philosophers of science of histime. However, it is precisely this preoccupation that has madeFleck so relevant for the sociology of science in the last two decades.As Barnes and Edge put it:

We do possess one fine pre-war work in the sociology of knowledgetradition which considered in detail the emergence of an accepted set ofscientific doctrines and techniques. Ludwik Fleck's 'Genesis andDevelopment of a Scientific Fact' (1935), recently rescued from oblivion,has been recognized as a major contribution. But that an extended studyof such insight and importance was largely passed over upon its firstappearance merely reinforces the point already made: there waswidespread reticence to investigate the basis of anything considered tobe genuine knowledge (Barnes and-Edge, 1982,65).

And because the 'set of accepted doctrines and techniques' studiedin great detail by Fleck in his magnum opus was, in his words, 'oneof the best established medical facts: the fact that the so-calledWasserman rection is related to syphilis' (Fleck 1935a: xxviii), hisstudies are of special interest for sociologists of medicine.

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The importance of medical examples in Fleck's works

Ludwik Fleck is viewed today as a pioneer of constructivistepistemology and of the sociology of the natural sciences. For thisreason, although all his sociological and philosophical studiesprincipally used examples taken from the history and the practice ofmedicine, his works are read almost exclusively by philosophers andsociologists of science, not by sociologists or philosophers ofmedicine. Even the few articles dealing with Fleck's views onmedicine have discussed Fleck's general philosophical position andmade no specific comments on his detailed descriptions and analysesof medical practice (Sadegh-Zadeh 1981; McCoullogh 1981), andmedical sociologists have quoted Fleck's book as an example of a'general discussion of the sociology of science' (Lipton and Hershaft1985). The numerous medical examples in Fleck's works have been,as far as I know, examined only in the framework of studies of hisoverall epistemological thesis. In my opinion, this is unfortunate.Fleck was the author of original reflections on subjects such as thegrowth and the diffusion of medical knowledge, the influence ofpopular models of disease on expert ones, the relationships betweenlaboratory and clinics, and the mechanisms of specialization inmedicine. I consider many of these pioneering reflections ofsufficient value to be studied for their own sake, and not only asillustrations of a general philosophical or sociological thesis. My aimis therefore to analyze Fleck's vision of medicine, and to selectamong his ideas those that I consider of interest for sociologists ofmedicine today.

In doing so I am aware of the fact that my presentation of Fleck'sreflections, which stresses the potential value of his ideas for thestudy of the specific problem of the growth of medical knowledgerather than the more general problem of the evolution of scientificknowledge, is not entirely faithful to Fleck's original intentions.Fleck based his reflections, at least as far as modern science isconcerned, on examples taken almost exclusively from his ownscientific discipline. His first epistemological study was an article onthe specificity of medical thought. But later on, he enlarged thescope of his reflections to all the natural sciences and he used theformation of medical knowledge as but one example of scientificknowledge in general. Fleck himself recognized, however, that hisreflections on the social origins of cognition were particularly welladapted to studies of the development of medical knowledge. Forhim 'medical problems, concerned as they are with Man's more

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highly prized possessions - his life and well-being - have anindividual and social significance such as is not directly within theprovenance of any physical or chemical problem. ( . . . ) This is whymedical science is more suitable for the investigation of the socialconditioning of cognition and acquired knowledge' (Fleck 1935b).In addition. Fleck's most important work. Genesis and Developmentof a Scientific Fact, is a detailed study of the development of aserological reaction for diagnosis of syphilis, i.e. a study of theapplication of fundamental immunological knowledge to practicalmedical needs. He founded many of his theoretical reflections on thisexample. For this reason, many of Fleck's ideas are, in my view, ofparticular pertinence to studies of interactions between fundamentalresearch and its practical applications in general, and morespecifically to studies of the development of medical knowledge.

Flecks ideas on medicine: The social origins of the disease concept

According to Fleck, the concept of disease is socially constructed.Inspired, in all probability, by the works of anthropologists (Fleck1935a: 46), he claimed that different cultures have different ideas ofhealth and disease:

There are cultures, as for example the Chinese culture, which in_ important fields, such as medicine, arrived at quite different realities

from those of us westerners. Shall we punish them for this with pity?They have had a different history, different aspirations and demandsthat are decisive for their cognition (Fleck, 1929).

Within Western civilisation, too, the definition and the under-standing of a given disease has varied over time. The first chapter ofFleck's book is dedicated to the analysis of the evolution of medicaldefinitions of syphilis in different historical periods, from the MiddleAges up to the present time. Syphilis was first defined as lues venerea.This definition did not differentiate between various venerealdiseases, and did not include tertiary syphilis. Later another,pharmacologically-inspired, approach was developed, which includedsyphilis among the diseases that were cured by mercury. Finally, atthe beginning of the 20th century the etiological definition ofinfectious disease isolated a specific set of pathological symptomsthat were united in a single disease concept 'syphilis', because all ofthem were induced by the same microorganism, Treponemapallidum (Fleck 1935a: 1-20). The different definitions of syphilis in

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distinct historical periods were, according to Fleck, deeply influencedby the dominant beliefs and traditions of a given time and 'the specificstate of mind of a given society was the first and the most decisivefactor that allowed the manifestations of morbus proteiformis to betransformed into a single unit, a well defined concept' (Fleck 1934).

Fleck did not limit these ideas to past definitions of disease. Forhim, present definitions were equally historically-conditioned.'They are the way they are because of just this particular history.Even the modern concept of the disease entity, for example, is anoutcome of precisely such a development, and by no means the onlylogical possibility'. And, 'as history shows, it is feasible to introducecompletely different classifications of disease' (Fleck 1935a: 21).

On incommensurability in medicine

According to Fleck, the classification of diseases is not a 'natural'one, referring to entities existing 'out there' and awaiting to bediscovered. For him, 'The so called diagnosis - the filling of a resultinto a system of distinct disease entities - is the goal and thisassumes that such entities actually exist and that they are accessibleto analytical method' (Fleck, 1935a: 64). Diseases are 'ideal,fictitious pictures, known as morbid units, round which both theindividual and the variable morbid phenomena are grouped,without, however, ever corresponding completely to them (Fleck1927).

Moreover, according to Fleck, such different 'fictitious pictures',i.e. different concepts of disease, do coexist, not only in differentcultures but also inside a given culture. The coexistence of differentconcepts of disease is the consequence of the very nature of thesubject. Because of the complexity and the highly individualcharacter of pathological phenomena, it is impossible to reducepathology to physics, chemistry or even to biology. To the alreadygreat difficulties of the study of normal living organisms, pathologyadds the supplementary ones of multifactorial and time-dependentphenomena. It implies, therefore, according to Fleck, a higher levelof complexity, and in consequence a higher degree of indeterminancethan biology. He affirmed that no simple causal relationship (thatcan be expressed as Cartesian coordiantes) exists in medicine, andin order to understand complex phenomena, such as disease, oneneeds to apply the principle of indeterminance developed by thetheory of relativity (Elkana 1986):

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Let me use a figurative comparison: medical thinking differs in principlefrom scientific thinking in that it uses Gauss's coordinate system, whilethe latter uses the Cartesian system. Medical observation is not a pointbut a small circle. ( . . .) A certain correction is introduced into thepicture by the fact that, strictly speaking, the multiplicity of medicalphenomena can be only approximately rendered by means of Gausssystem since its points are not univocally determinable. To all intentsand purposes, scientific thinking uses, for small ranges, the Cartesiansystem, and for large ranges Gauss's system (as in the theory ofrelativity). On the contrary, medical thinking uses Gauss's system forsmall ranges, while in the entirety it does not find any consistent andrational way to grasp phenomena.

The impossibility of elaborating a global medical theory whichallows for understanding of all the observed phenomena, 'like theatomic theory in chemistry or energetics in physics', makesimpossible the development of a single approach to disease:

Neither cellular nor humoral theory, nor the functional understandingof diseases alone, nor their 'psychogenic' conditioning, by themselveswill exhaust the entire wealth of morbid phenomena. . . . this results inthe incommesurability of ideas which develop from the varying ways ofgrasping morbid phenomena, and which give rise to the fact that auniform understanding of morbidity is impossible (Fleck 1927).

For Fleck, this incommensurability of ideas in medicine is notonly a theoretical concept. It has practical consequences. Scientificfacts are socially constructed by distinct 'thought collectives', eachcomposed of individuals who share a specific 'thought style',incommensurable with others. This makes communication betweenthe different thought collectives difficult. Moreover, in practice, theadoption of a given thought style excludes the simultaneousadoption of a different one: according to Fleck, although a physiciancan relatively easily reconcile his practice with an interest in thehistory of medicine, it is much more difficult to reconcile clinicalpractice and a reductionist point of view:

It happens more frequently that a physician simultaneously pursuesstudies of a disease from a clinical-medical or bacteriological viewpointtogether with that of the history of civilisation, than from a clinical-medical or bacteriological one together with a purely chemical one(Fleck 1935a: 111).

The importance of training for the adoption of a given 'thought style'

Differences in ways of understanding a given problem or even

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observing a given object according to an adopted thought style alsoexist, according to Fleck, among the different medical specialities:

The art of observation is not a general one; it does not include all fieldsof science at the same time. On the contrary, it is always limited to onefield only. I knew an eminent surgeon, specializing in the abdomencavity, who needed only just a few looks and a few touches of theabdomen to diagnose the clinical state of the apendix vermiformisalmost infallibly, sometimes in cases when other medical men 'did notsee anything'. The same specialist could never learn how to distinguishunder the microscope mucus strips from the hyaline cast. I also knew abacteriologist who was an assistant lecturer in a large university; heperceived and recognized ever so minute morbid changes in inoculatedanimals, but was unable to tell a male mouse from a female one. (Fleck1935c)

Probably under the influence of the Gestalt psychology (Schnelle1986), Fleck developed the idea that the capacity of observation isacquired largely through a learning process. He therefore explainedthe differences in the perception of medical specialists by differencesin their training:

One has first to learn to look in order to be able to see that which formsthe basis of a given discipline. (. . .) Still more vivid is the necessity of aspecial training to acquire the ability to perceive certain forms e.g. indermatology. In this field, a layman who is capable of carrying out goodobservations in other domains, say, a specialist in bacteriology, does notdifferentiate and recognize dermatological changes. At first he listens tothe descriptions of dermatologists as if they were fairy tales, much as hehas the described object lying in front of him. (Fleck 1935c).

During their training and specialization future specialists adopt agiven thought style and learn to see reality in accord with it. Abeginning student looking at a microscopic preparation of bacteriahas no idea what he is supposed to observe there. A long training isneeded to teach him to be able to 'see' the right picture (i.e. forFleck, one in agreement with the current bacteriological tradition).Moreover, and this point is crucial to the understanding of Fleck'sconcept of incommensurability, training in one thought stylehampers one's ability to look at the same object from a differentpoint of view:

One could believe that the hypothetical research worker of Poincare,while having an infinite time at his disposal, would be simply a specialistof all trades, all sciences, thus being able to perceive specific forms in allfields. However, this is psychological nonsense, since we know that the

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formation of powers of perceiving certain forms is accompanied by thevanishing of the faculties of perceiving some others. (. ..) A physicianwho is professionally trained in observing the ever-changeable andwhimsical pathological forms is, as a rule, a poor observer of continuallyrecurring regular phenomena: he is not interested in them, nor does henotice them, nor ought he to notice them if he is to be a goodpathologist. (Fleck 1935c).

During the process of specialisation in medicine, knowledge isgained and lost:

Physicians know that a dermatologist observes different things than ageneral practitioner. A general practitioner is unable to see the tinymodifications in the skin's surface, but is trained to perceive the generalhabitus of a patient, and can observe many things about him, invisiblefor the dermatologist (Fleck 1934).

Each medical specialist is able to observe pathological phenomenaonly in the framework of the specific thought style in which he wastrained. And each thought style 'made possible the perception ofmany forms, as well as the establishment of many applicable facts.But it also rendered the recognition of other forms and other factsimpossible' (Fleck 1935a: 93).

To sum up, for Fleck the intrinsic complexity of the subjectmatter of medicine - human disease - makes necessary thecoexistence of several distinct and incommensurable thought stylesdealing with pathological phenomena. Their incommensurabilitycan be explained at the cognitive level by the impossibility of findinga single explanatory theory able to embody the whole richness ofpathological phenomena, and at the sociological level, by theprocess of specialization in medicine, during which the increase incapacity to recognize some phenomena is necessarily accompaniedby the loss of the ability to perceive others.

Purpose-dependency of scientific truths and the medical way ofthinking

Medicine is a 'practical science' and, according to Fleck, its practicalgoals influence the development of medical knowledge. He illustratedthis claim by an example taken from bacteriology. According tohim, in bacteriology two distinct thought styles coexist: thebotanical-genetic and the medical-epidemiological. The bacteriol-ogists involved in botanical-genetic (i.e. scientific) studies of

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bacteria have a tendency to use stringent biochemical criteria in theclassification of bacteria. They prefer to have false negative results,rather than false positive ones. Epidemiologists, conversely, preferto have less stringent criteria, as they wish above all to avoid falsenegative results and the non-recognition of a potentially dangerousbacterium. Fleck quotes a study in which, during an epidemic ofscarlet fever the epidemiologists, using their criteria, classified 100per cent of the bacteria involved as Streptococcus haemoliticus.When the same bacteria were studied with the more stringentcriteria of fundamental bacteriology, only 84 per cent of them wereso defined. This story served for Fleck to illustrate 'the purpose-dependency of scientific truths'. For him the medical-epidemiologicalthought style is as legitimate as the botanical-genetic one; therefore,both results are correct, and 'one arrives at divergent and notinterchangeable truths' (Fleck 1929). Each one will be valid withinthe thought style that generated it. The truth of the fundamentalscientist is not, however, identical with the truth of a practicingmedical bacteriologist.

Medical practice and the problem of communication betweenthought collectives

What then can be done, when representatives of two distinctthought styles, holding these divergent and non-interchangeabletruths, need to communicate? This is a frequent situation inmedicine. General practitioners need the specialist's informationand they have to communicate it to patients. But, according to Fleck,patients (i.e. lay persons), general practitioners and specialists belongto different thought collectives and have distinct, incommensurablethought styles. Fleck analyses this situation through a concreteexample: the diagnosis of diphtheria. An expert bacteriologistdiscussing with another expert a specimen from a throat swab willindicate that many, but not all, of the bacteria in the studiedpreparation have the characteristics of Loffler baccilus, the etiologicalagent of diphtheria:

Numerous bacilli, many of them club-shaped and slightly curved (.. .)their arrangement is in several places finger- and pallisade- shaped,elsewhere irregular ( . . .) Loffler methyl blue: many lacerated bacilli( . . .) sharply defined colonies, in which bacilli were found mostlytypical in their staining characteristics, morphology and arrangement.The expert's conclusion, as formulated for his peers is that in view of the

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origin of the examined material, and the morphological and culturecharacteristic of the bacilli, the diagnosis of Loffler baccili seemssufficiently well established (italics mine) (Fleck, 1935a: 113).

For Fleck this is the presentation of an extremely simplified case.From his experience as a bacteriologist he knows that it is rare tofind that everything is in such perfect agreement. Often thearrangement of bacilli is not so typical, the staining is not sounambiguous and the culture may contradict the microscopicspecimen. But, even in the described ideal case, when the expertcan be as certain as possible that he is indeed dealing with diphtheriabaccili, the answer, formulated in the language of his specialty,would not, according to Fleck, appeal to a general practitionerexpecting a firm diagnosis. He may claim: 'I just asked you what thisthroat swab really contains, and you reply: because it is a throatswab the conclusion is justified that it is diphtheria. That isbeing mischievous. I wanted your support, but you used me tosupport yourself. Thus, the specialist would formulate a differentdescription for the general practitioner: 'the microscopic specimenshows numerous small rods whose shape and positions correspondto those of diphtheria bacilli. Cultures grown from them producedtypical Loffier bacilli'. And to the patient the description will beeven shorter: the doctor will simply state that he has diphtheria(Fleck 1935a: 114).

For Fleck, the specialists (the esoteric circle) and the generalpractitioners (the exoteric circle) belong to distinct thought collectives.Ideas that circulate among thought collectives are bound to changeduring this process. The uncertainty of the knowledge of specialistsis converted by the migration of ideas through the collectives into aheuristic vademecum science. It is characterized by the omission ofdetail and of controversial opinions which produces an artificialsimplification. The 'genesis and development of a scientific fact'described by Fleck - in this case the unambiguous affirmation that agiven person is suffering from diphtheria - is the result of thecirculation of ideas through thought collectives (Fleck 1935a: 112-13; 119).

Popular repr^entations of disease, vademecum science and expertmedical knowledge

According to Fleck, the circulation of ideas between thoughtcollectives is not one-sided. Scientific knowledge, when transformed

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into vademecum knowledge 'shapes specific public opinion as well asthe Weltanschauung and in this form reacts in turn upon the expert'(Fleck 1935a: 113). The main topic of Fleck's principal work.Genesis and Development of Scientific Fact is a study of the influenceof society on the formation of a specific 'medical fact': theelaboration of the Wassermann serological test for syphilis. Fleck'smain claim is that popular belief in the existence of 'syphilitic blood'provided a strong stimulus for the development of a blood test forthe diagnosis of syphilis. During the elaboration of this test, the firstexperimental results were, according to Fleck, far from encouraging.In addition, the results could not be fully explained by theimmunological knowledge of that time. But the authors of the testpersisted, and after many efforts were able to develop, by trial-and-error, a functional blood test. Fleck explains the persistence of thescientists, facing inexplicable findings and initial failures, by theinfluence of the centuries-long popular belief that syphilis inducesspecific modifications in the blood (Fleck 1935a: 11-13). In the early19th century, well before the discovery of specific antibodies in theserum, physicians tried to find chemical morphological modificationsin the blood of syphilitic patients:

With amazing and unprecedented persistence, all possible methodswere tried to confirm and to realize the traditional concept of syphiliticblood. It was with the so-called Wassermann reaction that the successwas at long last achieved (Fleck 1935a: 14).

This success was due to the existence of the popular belief:

Had it not been for the insistent clamor of public opinion for a bloodtest, the experiments of Wassermann would never have enjoyed thesocial response that was absolutely essential to the development of thereaction, to its 'technical perfection' and to the gathering of collectiveexperience' (Fleck, 1935a: 77).

However, the process did not come to an end at that point.Popular knowledge contributed to the formation of expert medicalknowledge, but later the newly formed expert knowledge wastranslated into a generally accepted vademecum knowledge. Thetranslation process is obligatory in medicine because this disciplineneeds to use fundamental scientific knowledge for the practical goalsof diagnosis and healing. In another part of his study of the originsand development of the Wassermann reaction. Fleck describes howexpert medical knowledge in this field became codified andsimplified, and achieved the status of vademecum knowledge. The

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selection, adaptation, simplification and transformation processesnecessary to accomplish this are made visible by Fleck by comparingthe first articles published by Wassermann and his collaborators inscientific journals (expert knowledge or 'journal science'), with thesimplified and codified representations of the Wassermann reactionin textbooks destined for clinical laboratory practice {vademecumknowledge) (Fleck 1935a: 70-6). When the expert knowledgebecame vademecum knowledge, i.e. was transformed into a'scientific fact', it acquired the capacity to modify the perception ofreality of those who utilized it:

In the history ofthe Wassermann reaction, we described the process bywhich personal and provisional journal science becomes transformedinto collective, generally valid vademecum science. This appears initiallyboth as a change in conceptual meaning and as a reformulation of aproblem, and subsequently as accumulation of the collectiveexperience, the formation of a special readiness for directed perceptionand specialized assimilation of what had been perceived (Fleck1935a: 120).

Fleck develops a highly dynamic vision of the formation ofmedical knowledge, in which expert knowledge is influenced bypopular knowledge, and then influences it in turn. According tohim, the modification and transformation of ideas is the obligatoryresult of their circulation through distinct thought collectivesholding incommensurable 'thought styles'. This modification ofideas has an important positive effect. When an idea belonging to agiven thought style is transposed to a different one, it'predominantlyfertilizes and enriches the alien style, while being altered andassimilated: the content changes sometimes beyond recognitioneven if the word has remained unchanged' (Fleck 1936). It cantherefore be at the origin of an innovation:

The intercoUective communication of ideas always results in a shift or achange in the currency of thought (.. .) The change in thought style, thatis the change in readiness for directed perception offers new possibilitiesof discovery and creates new facts (Fleck 1935a: 109-10).

In this way the old popular idea of 'syphilitic blood', whentransposed to a new thought collective - bacteriologists andimmunologists - allowed the development of an important innovation:the Wassermann test.

To sum up: for Fleck, medical knowledge by its very naturecannot remain an 'expert knowledge' confined to the Umitedthought collective of fundamental scientists. It needs to transform

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itself into a heuristic vademecum science, and to get into closecontact with popular representations of disease. The inevitabletransformations of expert medical knowledge that occur during thesocial process of its transmission and adaptation to the concreteneeds of medical practice can be at the origin of importantconceptual modifications and can lead to innovations in medicine.

Fleck's particular viewpoint

My hypothesis is that Fleck's ability to formulate a philosophicaland sociological approach to the evolution of medical knowledgehas its roots in the particularities of his professional situation at thetime he elaborated his theoretical views. In particular his owncareer, with a foot in medical practice and experience in scientificresearch, sensitised him, in all probability, to the disparities inthought style between different collectives (the 'clinical-medical' or'bacteriological' versus the 'purely chemical' viewpoint) and thusexamplified his own thesis.

Fleck was trained as a physician, but immediately after the end ofhis medical studies (in 1920) turned to fundamental research inbacteriology and immunology. He failed, however, to securehimself a position as a scientist, and was obhged to adopt a differentprofessional role: that of clinical microbiologist and immunologist.He was unable to keep his position at the Lwow University(probably either because of personal problems, or,the antisemitismprevailing at that time in Lwow, or both) and from 1923 to 1939 heworked in several routine analysis laboratories. Fleck considered thissituation as a temporary one and hoped to return to his truevocation: fundamental scientific research. He finally succeeded indoing so after the Second World War. During the years in whichFleck developed his epistemological ideas (1926-39) he dealt almostexclusively with practical questions and had limited, if any,recognition by fellow scientists. On the other hand he continued toview himself as a fundamental scientist. He pursued his scientificresearch during his free time, and hoped to return to the scientificcommunity (Schnelle 1986).

Although Fleck did not claim explicitly that his reflections werebased upon empirical studies, his professional experience allowedhim to use concrete and detailed examples taken from the dailypractice of a clinic, a hospital, a medical analysis laboratory. Inaddition. Fleck's marginal professional position during the period of

Ludwik Fleck 149

the evolution of his theoretical thought seems to have favored hisability to observe the development and the uses of medicalknowledge. His viewpoint was simultaneously an 'inside' and an'outside' one. It allowed him to combine the advantages of aninternal participant with those of an external observer. His specificposition - a fundamental scientist in a temporary (so he hoped)'exile' among practitioners - made it easier for him to observe theshortcomings and the difficulties of the application of science tomedicine. At the same time, his professional position gave him anintimate internal knowledge of what medical science is really about,and how it functions.

Conclusion

In this study I have tried to show the potential importance of Fleck'sideas for a sociological approach to studies of the formation ofmedical knowledge. Reck was among the first to postulate the socialorigins of concepts such as health and disease, normal andpathological. He explained, as many sociologists did later, thatdiseases are social constructions. But while medical sociologists haveusually stressed the impact of societal factors on the construction ofmodels of disease by patients (Zborowski 1953; Zola 1963; Goodand Delvecchio-Good 1981: 165-96; Mechanic 1982; d'Houtaudand Field 1984), Fleck was more interested in the study of theimpact of these factors on the construction of the disease concept byphysicians.

Through the detailed analysis of concrete examples taken fromhis professional experience, Fleck tried to explain some of themechanisms through which society can affect the process ofconstruction of medical knowledge. Some of these mechanisms havebeen studied by medical sociologists: the subject of the training ofphysicians and of their specialization and the effects of medicaltraining on doctors' professional behaviour was one of the 'classical'themes (Merton, etal. 1957; Becker, etal., 1961; Kendall and Selvin1966; Friedson 1970, Bosk 1979, Atkinson 1984). Today, probablyunder the influence of Kuhn's ideas concerning the effects oftraining in shaping scientific observation (Kuhn 1962), the impact ofpatterns of specialisation in medicine on the nature of medicalknowledge produced by physicians is also studied (Figlio 1982,Gabbay 1982). These studies, although they usually represent amore sociologial point of view than Fleck's epistomologically-

150 liana Lowy

oriented approach, can be viewed as a continuation of the researchprogram which he sketched.

However, Fleck's other ideas, e.g. the incomensurability of ideasexpressed by different thought collectives, the interactions betweenjournal knowledge, textbook knowledge and popular knowledge,and the transformation and modification of ideas during theircirculation through distinct thought collectives, have rarely beendeveloped. The differences between popular models of disease andscientific ones have been studied, but usually in order to explain thedifficulties in communication between doctors and patients (Loux1978: 311-15; Tuckett and Williams 1984; Tuckett, Boulton andOlson 1985). In addition, although some of these works have lookedfor a possible impact of scientific models of disease on popular ones(Samora, Saunders and Larson 1966, 292-301; Svarstad 1979;Morgan and Spanish 1985), less attention has been paid to a possiblereverse influence.

Fleck, a convinced holist, claimed that the formation of medicalknowledge was a time-dependent, dynamic process including manycomplex interactions and involving not only the limited circle ofmedical experts but society as a whole. Only the combination ofhistorical, sociological and philosophical approaches into a multi-disciplinary approach, called by him 'comparative epistemology',could allow for a proper study of such a complex phenomenon(Fleck 1935a: 22-3; 51). The detailed medical examples in hiswritings give us a glimpse of such a multidisciplinary approach to thestudy of the social genesis of medical knowledge. On the other handFleck's concept of complex dynamic interractions and mutualinfluences between popular science, vademecum knowledge andexpert medical knowledge can perhaps contribute to a betterunderstanding of the development of both scientific and lay modelsof disease. This may be of particular importance in studies ofdiseases which have a strong social impact, such as cancer or AIDS.

Fleck's epistemological writings suffer, in my opinion, fromseveral imperfections. They are in many aspects closer to a draftthan to a completed theory (Baldamus 1977; Harwood 1986). Someof the fundamental philosophical questions are not clearly answeredand the meaning of the expressions 'thought collective' and 'thoughtstyle' fluctuates in different contexts. These imperfections can be atleast partially explained by difficult conditions: life in a provincialtown, a marginal institutional position, and lack of contacts withphilosophers and historians of science.

The imperfections of his work notwithstanding. Fleck had the

Ludwik Fleck 151

undoubted merit of being among the first to ask fundamentalquestions about the social origins of scientific knowledge, and tracesome of the possible directions in which one can look for answers tothese questions. Moreover, many of his ideas can be tested withsociological methods. In his forward to the English translation ofGenesis and Development of a Scientific Fact, T. Khun affirmed thatmany of the issues evoked in this book 'merit much additionalconsideration, not the least because they can be approachedempirically. ( . . . ) Fleck opens avenues for empirical research'(Kuhn 1979: ix-x). In this article I have tried to show that thissuggestion can be particularly fruitful for sociologists interested inmedicine and in medical science. Fleck should not be viewed bythem as a hitherto 'unacknowledged precursor' brought to light byzealous historians of science (Metzger 1937), but as an author whoinvites them to future reflection and study.

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