BAcrziOwGcIcAL REVIEWS, June 1976, p. 276-283Copyright © 1976 American Society for Microbiology

Vol. 40, No.2Printed in U.S.A.

Robert Koch and Two Visions of MicrobiologyM. PENN AND M. DWORKIN*

University College and Department ofMicrobiology,* University ofMinnesota, Minneapolis, Minnesota 55455

INTRODUCTION ................ ................................ 276WAKSMAN ON THE TWO VISIONS ......................................... 277PLEOMORPHISM: KOCH VERSUS WINOGRADSKY .......... ............... 278PROCESS AND ESSENCE IN MICROBIOLOGY ............ ................. 279CONCLUSIONS ............... ................................. 281LITERATURE CITED .............. ............................. 282

INTRODUCTION

Microbiologists who wish to reflect on the lifeand works of Robert Koch may encounter asituation that, for all of its apparent irony, isalso instructive. In comparison to the searchingportrayals of the physics of the latter 19th andearly 20th centuries, with its schools, factions,and contentious figures, there is a remarkabledearth of critical, interpretive commentary onKoch's scientific accomplishments. One mayfind occasional cursory references to "hothousecultures" (12), to the narrow, oversimplifyingscope of his experimental investigations (16),and to the absence of original, innovative brilli-ance that we have come to expect from thegreat men of science (9), but always buriedbeneath avalanches of justifiable praise forKoch's renowned attainments in the etiology oftuberculosis, anthrax, and cholera. Toweringabove all else is the invariable reference to theformulation of Koch's postulates, which seem tohave set the course for the subsequent develop-ment of microbiology.One receives the overall impression that

large expanses in the history of microbiology,certainly the period in which Koch flourished,are periods of such incontestable achievementthat they tend to preempt the formulation ofalternative points of view. The impact of Kochhas indeed served to overshadow the influenceof other, possibly conflicting, conceptions of mi-crobiology current during his time. It is ironicthat the achievements which recall his great-ness, recited countless times in general histo-ries and textbook introductions, have obscuredthe broader, historical context in which heworked, especially his relation to contemporar-ies engaged in nonmedical research, making itdifficult to realistically assess his place in thegrowth of microbiological theory.Our attempt to treat Koch's contribution in a

conceptual-historical fashion has been madedifficult by the rarity of analytic histories ofmicrobiology that include more than an archi-val account of his work, or in fact challenge the

assumptions upon which it rests. To complicatematters further, Koch's own reticence to en-gage in a systematic evaluation of the activi-ties of microbiologists outside of his special-ized area of medical microbiology has alsohampered our inquiry into various conceptualaspects of his investigations.

Our concern is not to rehearse known factsrelevant to the Koch of history, but given suchfacts, to devise a framework of interpretationthat may yield fresh insights into their signifi-cance. We believe there is evidence to suggestthat emerging alongside the Koch tradition in19th century microbiology, was another com-peting, distinctive, and less conspicuous tradi-tion associated with the name of Sergei Wino-gradsky, the masterful Russian soil microbiolo-gist. Between Koch and Winogradsky therearose crucial and wide-ranging differences infundamental outlook on the experimental phi-losophy and goals of the microbiological disci-pline. An essential symptom of these differ-ences was the technical issue of the use of pureversus mixed cultures. This apparently simplemethodological difference has not only deter-mined, to a great extent, the content of microbi-ology, it has also hidden from view a series ofassumptions we wish to discuss further in thispaper. These include the vision of microbiologyas a science whose subject matter is the isolatedmicrobe, and the view that from the individualproperties of the isolated microbe the dynamicnature of complex populations can be deduced.A further difference between Koch and Wino-gradsky concerned microbiology as either a sci-ence with an intrinsic content, or one that isexclusively instrumental in the solution of ap-plied problems.

Finally, the ancient question of pleomor-phism was intimately connected with the un-derstanding of the microbe as a static, isolatedorganism as contrasted with the more dynamic,interactive view of Winogradsky.Far from diminishing Koch's stature, the ex-

istence of another, provocative viewpoint testi-fies to the rich and varied character ofmicrobio-

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logical thought prior to the advent ofthe molec-ular revolution in biology. But it is not ourintention to claim that where one ofthese tradi-tions has succeeded the other failed, and thatcontemporary microbiologists must contendwith an irreparable historic split with its at-tendant mood of conflicting ideologies and alle-giances. We believe, on the contrary, that it isless a question of the special merit of one ofthese traditions than of the need to reflectbroadly and synoptically on the relation be-tween them. The significance of Koch's workrequires clarification, and we shall now sketchsome of the larger assumptions underlying thetwo traditions.

WAKSMAN ON THE TWO VISIONSOur contention that at the outset of the 20th

century more than one distinctive conception ofmicrobiology began to unfold derives from twosources: the critical reminiscences ofWaksman(11-16), and evaluations of Koch's achieve-ments that were the subject of intense discus-sion over a lengthy span from about 1882 (thedate of publication of his original paper on the.etiology of tuberculosis), into the second andthird decades ofthe 1900s. Some observations ofTheobald Smith and Winogradsky during thisperiod are also especially relevant (10, 17).Waksman does not present a systematic and

detailed narrative of the specific relationshipbetween Koch and Winogradsky. We do find amontage of retrospective impressions ratherthan a coherent evaluation of their contribu-tion. In "Microbiology-Yesterday and Today"(15), for example, he reflects broadly upon theimpact of F. Cohn, Winogradsky, and Beijer-inck, whose interests in botany and agricul-tural science were intensely theoretical, but isunclear in his account of the place of Koch andWinogradsky, whom he lumps together (in ourview, indiscriminately) under the rubric of the"older microbiology." His reason for doing somay have been to contrast sharply the "newmicrobiology" with its emphasis upon geneticsand biochemical processes, as against the olderinsistence upon the anatomy and physiology ofcells. Yet there are, we contend, crucial differ-ences within the "older microbiology" that hefailed to explain.

In various places he provides an excellentalthough piecemeal basis for understanding theconflicting features of the Koch and Winograd-sky traditions. "The Changing Concept in Mi-crobiology" (13) contains striking allusions to"two approaches." One approach, the "pure cul-ture concept," involves the notion that the ana-tomic structure and physiological behavior of

pathogens may be determined from an orderedexamination of the single cell, isolated in acontrolled medium (13). There is, on the otherhand, the theory of microbial association ac-cording to which the chemical activities of anorganism depend upon its complex and variedrelationships with other organisms (13). In onecase, what is stressed is the physically andphysiologically independent cell, whereas inthe other it is the associative dependencies of amixed population of cells. Waksman restrictshis account of the "two approaches" to appliedproblems of disease, and concludes that theinvestigation of interactions among mixed cul-tures has, to use his words. "supplemented andeven partly replaced ... practical developmentsof disease control resulting from the work ofPasteur, Koch and Kitasato . . ." (13).Apart from these altogether terse references

to Pasteur, Koch, Kitasato, etc., Waksmandoes little to explain the conceptual origins ofthe "two approaches" or undertake a fine-grained analysis of their relation. We learnthat Pasteur is the source of both, one strand ofwhich was further developed by Koch, and al-though he also cites historic figures associatedwith the other, i.e., Ehrlich, Domagk, Trefouel(13), he fails to make explicit mention of Wino-gradsky's decisive contribution to the theory ofmicrobial association. What we wish to deter-mine, however, is the presence of ideas thatunderlie the work ofKoch and those with whomhe may have fundamentally differed, and inthis respect, observations of Waksman foundelsewhere are more helpful."The Microbe as Biological System" (12)

brings various antagonistic aspects of both "ap-proaches" into clearer focus. Waksman refers tothe pure-culture concept as "the sine qua non ofthe microbiologist" (12), and as "one of the fun-damentals of Koch's postulates, the ten com-mandments of bacteriology" (12). In spite of thefact that ".. . virtually all textbooks have ac-cepted these postulates without question" (12),and ". . . the impression that one gains from aperusal of the scientific literature in the field ofmicrobiology is that microbes can hardly bestudied except in pure cultures .. ." (12), helimits the role of pure cultures to problems ofdisease or their practical use in industrial proc-esses: "The available information on the role ofmicrobes in living processes has thus becomeclassified if not codified entirely on the basis ofpure culture studies. This may be justifiableand even essential in the consideration of mi-crobes as causative agents of disease and ofmethods for combating them, as in the utiliza-tion of microbes for the manufacture of chemi-cal compounds .. ." (12). But from the theoretic

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standpoint, ". . . it is hardly sufficient, except asmere supplementary information, in the studyof the many natural processes carried out bymicrobes, as in the soil, the residual wastes ofplant and animal life, in water basins, in sew-age disposal plants, and in many other sub-strates" (12). Waksman points out that thenumber and kinds of nonpathogenic organismsencountered in nature far exceeds the patho-gens studied in a pure-culture microbiology: "Itneed not, therefore, appear strange to empha-size the fact that the great majority of microbesare found in nature and carry out their normalactivities not in pure cultures, but in mixedpopulations. One may recall in this connectionthe remark of Winogradsky that some bacte-riologists deal with hothouse varieties of bacte-ria, far removed from their naturally occurringprogenitors, and would hardly recognize themwhen found in their natural milieu" (12).

Koch's astounding claim that the cause oftuberculosis is identical in humans and ani-mals, and that disparate clinical manifesta-tions may be rationalized by means of a single,comprehensive etiology (8) represents an at-tempt to establish an etiological structure rarein the history of the biomedical sciences. Buteven if Koch were correct and the tuberclebacillus is viewed as the sole, unitary cause ofcomplex intra- and cross-species pathology, hefalls short of including in his network of expla-nation a wide range of nonpathogenic proc-esses. Perhaps the most that can be said, Waks-man seems to argue, is that the pure-cultureisolation of organisms happens to have beenrestrictively successful in the case of some in-fectious diseases, but that it has not satisfiedthe need to understand the fundamental biolog-ical and chemical character of microbial proc-esses.Waksman seems, therefore, to have been in-

clined to distinguish a practically oriented mi-crobiology, however it may enrich our ability todeal with microbial phenomena, in contrast toa theoretical microbiology which emphasizedthe study of the intrinsic activities of microor-ganisms. He retains the distinction in "An In-stitute of Microbiology - Its Aims and Pur-poses" (11), observing that Koch's interest inmicrobiology was "not as a fundamental sci-ence, but rather in its applications" (11). It isinteresting to note that even in the half centurythat elapsed after the publication of the "Etiol-ogy of Tuberculosis," Waksman could still ex-press anxious concern over the proper contentof Microbiology. "Microbiology, it may be said,has not yet come into its own" (11), and thereason given to explain this strange indecisive-ness is that". . . microbes were considered (by

Koch and also Pasteur, 'the two greatest earlybacteriologists'), as agents responsible for cer-tain diseases or for certain important naturalprocesses; they were to be either encouraged ordiscouraged, whichever the case may be, butthey were to receive only scant recognition asindependent biological systems" (11). This toneof long-standing crisis reflects his awareness ofthe broad clash between the two alternativeconceptions of microbiology. Viewed from theKoch standpoint, microbiology may be con-ceived as lacking a distinctive content of itsown. In traditional terms, "disciplines" requirean "object ofstudy" definable in principle. SinceKoch's interest in the microbe was aimed pri-marily at the control of microbial disease, mi-crobiology would inevitably be seen as a de-rived or "instrumental" science, without a pri-mary, delineable phenomenon which it exam-ines. Waksman is not clear on the sort of crite-ria which, if satisfied, would legitimize a scien-tific discipline, and specifically microbiology.But viewing microbial life as an intrinsic bio-logical and chemical phenomenon, complexlyrelated to other living things, and subject to thesame lawful regularities, seems an essentialrequirement. "In this institute particular at-tention will be devoted to the fundamental as-pects of the study of microorganisms, theirphysiology, their biochemical activities, andtheir relations to higher forms of life, notably toman and to his domesticated plants and ani-mals. In other words, microbiology will betreated as a fundamental science" (11).

PLEOMORPHISM: KOCH VERSUSWINOGRADSKY

References to Koch in the writings of Wino-gradsky are sparse and diffuse. Where he ismentioned, for the most part in contexts thatare critical and argumentative, we find a basisfor confirmation of Waksman's account of the"two approaches." Although Winogradskyagreed with Cohn and Koch in their contro-versy with the pleomorphists Naegeli and Zopf,he expressed dissatisfaction with attempts bythe former to establish the stability of bacterialspecies on the basis of a limited variety of orga-nisms cultured in artificial media (18). "TheDoctrine of Pleomorphism in Bacteriology"(1937) contains a subtle effort by Winogradskyto save the pleomorphism issue from the con-fusing treatment afforded it in the past by bothmonomorphists and pleomorphists. Winograd-sky's objective seems to have been to reformu-late and clarify the issue within the frameworkof an "enrichment" methodology. Both camps,he argued, fundamentally misconceive the

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matter: Naegeli and Zopf fail to recognize theexistence of 'morphological types" among bac-teria, and although Cohn and Koch verify theirexistence, they do so at the expense ofbewilder-ing kinds ofvariant bacteria that elude investi-gation by means of the "pure-culture" approach(18). Either one is forced to admit with Naegeliand Zopf the occurrence of unceasing bacterialvariation, in which case pleomorphism is true;or pleomorphism is false, as Cohn and Kochargued, in view ofthe uniform isolation ofiden-tical bacterial "forms" in pure media. Facedwith this impasse, i.e., the specter of chaoticbacterial variation, on one hand, and on theother, fixed bacterial types (18), Winogradskyelects to move to a middle position. The absenceof variation in living systems is inconceivable(18). But from this it does not follow that theycannot be systematically ordered into morpho-logical genera and species (18). Zopfs experi-mental results, moreover, are simply untenable(18). Aside from that, however, both camps failto grasp the evolutionary nature of microbialcells. Winogradsky observes that ". . . the ideason bacterial morphology remained almost sta-ble within the limits ofthe so-called Cohn-Kochthesis. This was due, perhaps, not so much to acorrect biological conception ofthe characters ofa species, as to the use of standardized culturemedia" (18). Koch was right, not as sometimeshappens, for the wrong reasons, but perhaps ofgreater interest, in spite of the lack of a tho-rough-going biological explanation supportive ofhis position. This requisite and general "biolog-ical conception" may be found in the botanistdeBary whom Winogradsky quotes: ". ... contin-ued investigation has now, it may well be as-serted, supplied the answer, namely that in thearea in question, the situation with regard tospecies and their differentiations is no differentfrom what it is in other areas of nature descrip-tion ... species are distinguished by their evo-lution cycle. The totality of individuals andgenerations which during the period of observa-tion available, show the same periodically re-peate4 evolution cycle by the forms which suc-cessively appear in it. These form the charac-teristic.features for the recognition and differ-entiation of species .. ." (2).The proponents of pleomorphism are correct,

insofar as their doctrine when reformulated canbe understood to emphasize variation and fluc-tuation of species. But they are wrong, insofaras their initial position, when taken to its logi-cal conclusion, would undermine the possibilityof a systematic study of bacterial organisms.Furthermore, there can be no doubt, accordingto Winogradsky, that Cohn and Koch helpedopen the way to a systematic study of bacteria:

"The recognition that this group of elementaryorganisms is subject of botanical differentia-tion, as is every other group of cryptograms,was certainly a great achievement of the time.... Robert Koch, an early medical disciple of F.Cohn, applied his views to pathogens, with thebrilliant success that is well known" (18). Onthe other hand, their attack on pleomorphismreveals, in Winogradsky's view, some essentialshortcomings of the pure-culture method. Torefute the radical pleomorphism of Naegeli andZopf, what must be shown is that the appear-ance of dangling variations signals nothingmore than developmental stages in an orga-nism's "evolution cycle" (18). If bacteria areviewed not as static entities, but in develop-mental terms after the manner of Winograd-sky, such variations could be seen as a continu-ous and stepwise unfolding of forms in the evo-lution cycle. In this fashion, Winogradsky laidthe foundation for a dynamic morphology cen-tered on the concept of a morphological type("biotype"), while viewing apparent pleo-morphic novelty as a dynamic variation fromthe type (18). The resolution of the pleomor-phism question will be found in the conditionsunder which evolutionary modifications of thebiotype take place, drawing as far as is feasibledeviations from it into a patterned succession ofspeciated forms: "To disentangle the biotypefrom the variants and to discover the conditionsunder which it is able to display a regularcourse of evolution, is to be regarded as the firsttask of the morphologist" (18). However, thedrawback inherent in the pure-culture ap-proach is that no provision is made for bacterialvariation, or of the conditions which determinefundamental processes of this sort: "In compar-ing the bacteriological pure culture methodwith the old botanical method, where stresswas based on continuous observation of selectedcells or groups in microculture, the latter pre-sents decided advantages for the study of nor-mal evolution, by following step by step thedevelopment of the strain and by comparison ofthe stages with the growth found in the naturalhabitat..." (18).

PROCESS AND ESSENCE INMICROBIOLOGY

In Winogradsky's account of pleomorphism,we witness the rise of a distinctive mode ofmicrobiological thought. We may call it the"interactive" in contrast to the "essentialist"mode characteristic of Koch. By "essentialist"we mean, roughly, the view that conceived ofmicrobial cells as independent entities possess-ing an intrinsic anatomic and physiological

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scenario, knowledge of which would be ade-quate for an understanding of their behavior.The "interactive" view, in contrast, emphasizedprocess and sequential change as a persistentfeature of microbial phenomena. In this view,furthermore, single cells are always located incell populations, and their physical and chemi-cal properties derive, accordingly, from variousinteractive processes within the population. Wehave seen an example ofthe "interactive" modein Winogradsky's scheme for bacterial varia-tion. Variation of the sort advocated by radicalpleomorphists makes no sense. Variation,strictly speaking, involves change relative to anorm or type, i.e., the "biotype." The evolvingbiotype consists of a graduated sequence offorms integrally related to each other and to thebiotype in which they originate. We have im-plied that a morphology ofthe sort which Wino-gradsky seems to have advocated combines"form" and "process," two seemingly inimicalnotions that had long plagued the classical tax-onomists, and may have surfaced in the contro-versy over pleomorphism.Some of Koch's general views on morphologi-

cal differentiation serve as an example of the"essentialist" position. He maintained the ex-istence of fixed bacterial species:

The greatest stress, in investigations on bacte-ria, is justly laid on the so-called pure cultiva-tions, in which only one definite form of bacte-rium is present. This evidently arises from theview that if, in a series of cultivations, thesame form of bacterium is always obtained, aspecial significance must be attached to thisform: it must indeed be accepted as a constantform, or in a word, as a species (1).

Koch believed also that bacterial form pertainsexclusively to the morphology and physiology ofindividual cells:

As, ... there corresponds to each of the dis-eases investigated a form of bacterium dis-tinctly characterized by its physiological ac-tion, by its conditions ofgrowth, size, and form,which, however often the disease be transmit-ted from one animal to another, always re-mains the same and never passes over intoother forms, e.g., from the spherical to the rod-shaped, we must in the meantime regard thesedifferent forms of pathogenic bacteria as dis-tinct and constant species (1).

Bacterial form is, therefore, a continuous fea-ture of individual cells comprising a species.But in addition to morphological identity, thecausal bond that holds between differentiablepathogens and specific diseases also contrib-uted to their speciation:

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At the same time, the bodies of those animalswhich died of the artificial traumatic infectivediseases contained bacteria in such numbersthat the symptoms and the death of animalswas sufficiently explained. Further, the bacte-ria found were identical with those which werepresent in the fluid used for inoculation, and adefinite form of organisms corresponded in ev-ery instance to a distinct disease ... even in thesmall series of experiments I was able to carryout, one fact was so prominent that I mustregard it as constant, and as it helps removemost of the obstacles to the admission of theexistence of a contagium vivum for traumaticinfective diseases, I look on it as the most im-portant result of my work. I refer to the differ-ences which exist between pathogenic bacteriaand to the constancy of their characters. Adistinct bacteric form corresponds, as we haveseen, to each disease, and this form alwaysremains the same, however often the disease istransmitted from one animal to another (1).

Koch thus advanced two separate but relatedcriteria establishing bacterial species: morpho-logical identity, and the ability of bacteria toproduce distinctive disease. Contrary to ourpresent contention, however, he seems to havealso expressed an interest in more than theindividual bacterium:

. . . the differences between these bacteria areas great as could be expected between particleswhich border on the invisible. With regard tothese differences, I refer not only to the size andform of bacteria, but also to the conditions oftheir growth, which can best be recognized byobserving their situation and grouping. I there-fore study not only the individual alone, butthe whole group of bacteria, and would, forexample, consider a micrococcus which in onespecies of animal occurred only in masses (i.e.,in a zooglea form), as different from anotherwhich in the same variety of animal, under thesame conditions of life, was only met with asisolated individuals ... (1).

But it is evident that Koch's conception of a"grouping" of bacteria is precisely that of hisisolated, individual bacterium. The fact thatthe micrococcus may appear in groups or singlyis not something for which he sought an expla-nation, either from the standpoint of its rela-tion to the animal host (3-6), natural environ-mental conditions (3-6), or in view of cellularinteractions within the micrococcal group. Heobviously believed that the occurrence of orga-nisms singly or en masse must be demonstratedexperimentally. Beyond that, he does notundertake an explanation of cellular pheno-mena of this sort.

Winogradsky's"interactive" outlook led him

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to a different conception of bacterial speciation.Koch, as we have seen, based his account uponthe morphological form of individually existingpathogens. Winogradsky, on the other hand,based his study of species upon cellular interac-tion, in place of the single, isolated organism(14). Like Koch, be believed that the orderlyinvestigation of bacteria required the idea ofstable species. But whereas from Koch's stand-point microbial "form" amounted to generalizeddescriptions of specific and invariant varietiesof microbes, it was, for Winogradsky, a conven-ient designation for intricately different con-stellations of cells competitively adapting tovarying environmental conditions (14). If Kochstressed the differentiating characteristics ofsolitary organisms, Winogradsky hoped to for-mulate a systematic theory of their communalinterrelations. We do not think it excessive toclaim that Winogradsky may have been amongthe earliest modern biologists to have wrencheda biological discipline from its roots in a Lin-naen vision of fixed animal "essences," prepar-ing the way for a chemical study of collabora-tive microbial activity.

CONCLUSIONSWe have sketched various historical aspects

of the contribution ofKoch and Winogradsky tothe development of microbiological thought.We now conclude with a summary discussion ofsome main issues that emerge from a consider-ation of the relation between the two visions ofmicrobiology.

First, we have seen how the microbe, havingbeen treated as instrumental in the control ofinfectious diseases, is subsequently conceivedby microbiologists in the Winogradsky tradi-tion as an intrinsic biological phenomenon. Ad-vances in the understanding of the molecularbasis ofmicrobial activity, however, have madeit possible for medical and industrial microbiol-ogists whose interest may be of the instrumen-tal variety to exhibit also a concern in the fun-damental character of the microbe. Although itmay appear that the differences between "Ko-chian" and "Winogradskian" microbiologistsamounts to the difference between "theoretical"and "applied" microbiology, we wish to empha-size that what we have described in terms ofthe"two visions" cuts deeper than the organiza-tional structure of the discipline. We in factbelieve that it would not be unrealistic to claimthat the future disposition of microbiology as ascientific discipline, together with its affilia-tions to other nonscientific intellectual pur-suits, requires a thoroughgoing evaluation ofthe "two visions" and ways of achieving theirunification.

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Second, the objection may be raised that ouraccount of conflicting differences between Kochand Winogradsky amounts to little more thandifferences in the use of an experimental tech-nique, in the one case, "pure," and in the other,"enrichment" cultures, and therefore from theoperational standpoint, microbiologists maywish to view themselves as adherents of bothtraditions. When describing what he calls "themicrobiologist of today" (15), Waksman himselfadmits as much: "Microbial populations, whenthey are considered at all, are studied from thepoint of view of single cultures, with all thecomplex reactions involving problems of resist-ance and sensitivity, parasitism, and saprophy-tism." Our contention that a principal differ-ence between Koch and Winogradsky consistsin their respective emphasis upon the singlecell isolated in pure culture, or variegated pop-ulations studied by means of enrichment tech-niques, seems in this light either trivial ormoot. The claim that far-ranging implicationsseparate the two traditions cannot withstandestablished and continued experimental suc-cess whether the approach taken is a la Koch orWinogradsky.But to this we reply that our intention was

not to argue the specific advantages of varioustechniques for the investigation of the microbe.On the contrary, the fact that, as Waksmaninsists, even mixed populations are sometimesbest understood in terms of "single cultures"demonstrates the needed unitary outlook whichwe advocate. Our observations concerning the"two traditions" were directed at possibly diver-gent modes of "explanation," and not at prob-lems that may arise in the course of the system-atic accretion of microbiological "technique."Perhaps we should distinguish generally be-tween "technique," on the one hand, and "ex-planation," on the other-a distinction thatmay help clarify the present argument. Putsuccinctly, the technical, empirical acutenessnecessary for the solution of a problem is onething; the ability to describe the principlesupon which the solution may be based is an-other. Procedures for the systematic isolationand identification of organisms are not to beconfused with preferred explanations of theirphysicochemical behavior. There is, so far aswe can see, nothing inconsistent in the applica-tion of pure-culture technique to mixed popula-tions of organisms, but there are crucial differ-ences at the level of explanation between Wino-gradsky's "interactive" model and Koch's "es-sentialist" mode of explanation.

Third, we wish to reiterate the differencesjust cited between the two types ofexplanationsand in order to make that difference explicit we

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present by way of contrast what we may callWinogradsky's "counter-postulates" listed inhis "Method in Soil Microbiology": (a) "Avoid,on principle, working with stock cultures; (b)use for experiments strains freshly isolatedfrom the soil by a method as short and direct aspossible; (c) supply them with nutrients thatcan be supposed to be utilized by them in thesoil; (d) make a special point of studying thereactions ofthe soil population as a whole, sincethe competition between its components is theprincipal determinant of their individual func-tions" (18). And in this context, it would beappropriate to refer to the prescient observa-tions of Theobald Smith in 1932:

... Aside from his special contributions, Koch'searly work marked the beginnings and fur-nished the foundations ofmodern scientific bac-teriology-the natural history of pathogenicbacteria. Though the experimental method wasintimately concerned, its chief function was toproduce pure cultures for morphological, sys-tematic, and ecological study. The vastly morecomplex physiological problem of their rela-tionship to the host and its tissues came inci-dentally in a disclosure ofhumoral and cellularforces in their relation to infection and immu-nity, and it still awaits more comprehensive aswell as analytic study. Since we must knowwhat we are working with all such more pene-trating analyses must be prefaced by Koch'smethods. They are here to stay and cannot bediscarded, since nature does not deal primarilyin pure cultures.We are passing now through a period as in-

teresting as that associated with Koch's earlycareer. Almost overnight the field of filterableagents of disease has become very extensive.Bacteriologists, tired of considering theirwards simply as elongating and dividing, tac-itly abandoning the conception that these schi-zomycetes are the non-sexual residues ofhigher forms, are building another hypothesiswith bacteria forming the brood sacs and germcenters of invisible, filterable forms. We havein our midst either a group of modern Kochs ordisciples of Naegeli. Only the future will tellhow to classify them (10).

Fourth, we find in the Winogradsky traditionthe first, clear attempt to explain on an empiri-cal basis the interactional complexities be-tween organisms and their varied environ-ments. If Koch stressed the morphophysiologyof organisms, then it would be accurate toobserve that subsequent microbiology moved tohost relationships, and finally in the presentera problems of environmentally inducedchange. An outstanding attempt to develop adistinctive, microbiological account of the "en-

vironment" may be found in the work of R.Dubos who has pioneered the introduction ofthe "environmental" concept in microbiology(3-6).Our goal generally has been to contrast two

historic traditions that have shaped the aevel-opment of microbiology. To Koch we owe anappreciation for the fine detail in microbiologi-cal inquiry, to Winogradsky the conceptualmeans to assemble that detail into a coherenttheory of living systems. We can think of nogreater tribute to Koch's memory than thestruggle to unite the two visions of microbiol-ogy.

LITERATURE CITED1. Brock, T. D. 1961. Milestones in microbiology.

Prentice-Hall, Englewood Cliffs, N.J.2. deBary, A. 1885. Vorlesungen uber Bakterien.

Leipzig.3. Dubos, R. J. 1959. The mirage of health, uto-

pias, progress and biological change. Peren-nial Library, Harper and Row.

4. Dubos, R. J. 1960. Health and Disease. J. Am.Med. Assoc. 174:505-507.

5. Dubos, R. J. 1974. Pasteur's dilemma-the roadnot taken. ASM News 40:703-709.

6. Dubos, R. J. 1968. Man, medicine and environ-ment. Frederick A. Praeger, Publishers, NewYork.

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