What general conclusions can be drawn about the reception of zymase, its relation to the larger shift from a protoplasm to an enzyme theory of life, and its status as a social phenomenon?The most striking and to me unexpected pattern is the close correlation between attitude toward zymase and professional background. The disbelief of the fermentation technologists, Will, Delbrück, Wehmer, and even Stavenhagen, was as sharp and unanimous as the enthusiasm of the immunologists and enzymologists, Duclaux, Roux, Fernback, and Bertrand, (...) and of Pfeffer, the experimental plant physiologist. Other skeptics—Voit, Kupffer, and Fischer—were conservatives in traditional fields. In all these cases it seems clear that professional commitments and outlook profoundly influenced the reception of zymase.In some cases there is a correlation with a specific earlier statement favoring the protoplasm theory or predicting a fermentation enzyme. Reynolds Green is a striking case of both. In 1893 he stated his belief that life processes in higher plants and fungi were identical, both being mediated by protoplasm.109 Thus he claimed that digestion was not carried out by enzymes, as in higher animals, but by the whole protoplasm, and so too fermentation in yeast: “All the metabolic processes must be carried out in the unicellular organism in the same mass of protoplasm.”110 But Green also insisted that there was no essential difference between “organized” and “unorganized ferments”; enzymes were simply more highly differentiated and specialized forms of primitive protoplasm. He spoke of “the alcoholic ferment” (that is, enzyme), and of intracellular enzymes—very advanced beliefs for 1893. Thus it is understandable why Green saw no reason to doubt his first negative results with yeast juice, and rushed into print. But it is also understandable that he persisted and soon became an outspoken advocate of Buchner's view; like Wroblewski and Pfeffer, he had already accepted the idea of an intracellular fermentation enzyme.The physiological chemists also fit the pattern in a special way. Physiological chemistry is generally regarded as the source of biochemistry; indeed, many early biochemists were trained in physiological chemistry, and imbibed there a progressive interest in enzymes and metabolism. It is not surprising, therefore, that on the whole Neumeister, Madfadyen, Wroblewski, and Loew accepted cell-free fermentation. But what is surprising, and significant, is the diversity of opinion in this group, from Abeles' living protoplasm to Wroblewski's organized array of active proteins. The feelings of the physiological chemists were mixed, and there was enough of the old protoplasm view in Macfadyen's and even Wroblewski's views to allow Buchner to see them as attacks on zymase. The ideas of physiological chemistry were also changing; the idea of protoplasm was already adjusting to the new interest in enzymes in the early 1890's. But in contrast to immunochemistry, the change in physiological chemistry was gradual, uneven, undramatic, and relatively invisible. For the new biochemistry, the tradition of physiological chemistry was the source of traditional conservatism as well as of new ideas of enzymes.In general, then, I claim that it was not experimental facts that determined attitudes toward zymase so much as previous commitments, experience, and expectations. Initially, at least, zymase was less a determinant of opinion than a touchstone of pre-existing opinion. Like a prism, it revealed the spectrum of existing attitudes toward vital phenomena.Also relevant here is the fact that the experimental evidence was entirely ambiguous; the interpretation of Buchner's experiments with antiseptics or dried yeast depended entirely on how far one was willing to stretch the scope of the terms “protoplasm” and “enzyme”. Likewise, how important one judged the instability of zymase to be, or the low level of in vitro activity, depended largely on one's point of view. There was no crucial experiment, no certain proof. Logically zymase could be regarded as protoplasm. A. Fischer did so in 1900;111 Macfadyen was still wavering in 1907;112 and Beijerinck was holding out as late as 1916.113 There were undoubtedly others. Besides the special case of Reynolds Green and the technologists, there are no recorded cases of conversion.But if there was no evidence to convert a dedicated protoplasmist, there was plenty to encourage a dedicated belief in the enzyme theory, and that, I believe, is precisely what happened. The arguments of Buchner et al in support of zymase had the greatest effect not on the protoplasmists but on those who were already predisposed toward the biochemical view. The zymase debate enabled the emerging group of biochemists to recognizethemselves as a group with a community of out-look and objectives; it brought the issue of protoplasm vs. enzyme into the open and gave it a specific and concrete issue on which to turn. The debate sharpened the biochemists' awareness that their point of view was becoming the new mainstream of biochemical thought.All this of course had an important secondary effect on those who opposed the new view, or who were not immediately concerned with it. After the zymase debate, it would have been almost impossible to ignore the new ideas; the dramatic and wide publicity the debate enjoyed would have made it difficult not to take sides. Buchner's successful defense of zymase itself became an important influence on opinion; the new movement had to be looked at with respect. But the primary effect of the debate, I assert, was on those who were already inclined to the new view. The outcome was not a mass conversion of individuals, nor the ejection of one idea by another. The sides probably did not change much; the real change was in the way each side regarded itself and its place in history. The zymase debate may perhaps best be regarded as a process of selection. Buchner's party became aware of itself as the new progressive point of view, while those holding the traditional view could no longer expound it publicly without appearing obstinate or old-fashioned. Thus the way was clear for the gradually wider establishment of the new ideas, especially among the new generation of biochemists. In this specific sense, the acceptance of zymase was a social phenomenon.This way of looking at the zymase debate also illuminates its coincidence with the emergence of biochemistry as a profession. The new professional trappings and organizations were the social manifestation of the new self-awareness gained from the zymase controversy. One of the most important effects on those disposed toward the new view was the awareness of an intellectual community and of the need to give that community social forms. The almost mythical importance of Buchner's “victory” over the old protoplasm theory that later became current is readily understandable. It was a useful ideology for a group anxious to assert the novelty of their approach, a novelty which they in fact felt quite keenly.But if the primary effect of the zymase controversy was on those predisposed to accept zymase, then obviously the success of zymase depended on the fact that change had already begun to occur. Indeed, one of the most striking, and again unexpected, results of this study is the extent to which the importance of enzymes was already recognized in the early 1890's. The new immunology clearly pointed the way. Macfadyen and Hans Buchner were looking for active proteins inside the cell in 1893. Reynolds Green, Wroblewski, and Pfeffer had all anticipated the discovery of a fermentation enzyme. Other discoveries in enzymology in the 1890's pointed the same way.114 Moreover, it is clear from this study that the old protoplams theory was adapting to the new discoveries concerning the importance of enzymes. The sidechains of the old protoplasm molecule were simply reinterpreted as enzymes, as in Wroblewski's theory, for example, or in Paul Ehrlich's extremely influential “sidechain theory” of antibody formation (1897). Despite the later views of Hopkins et al., the old protoplasm and the new enzyme theories were not irreconcilable; a continuity of development had already begun when zymase came so dramatically on the scene. Buchner himself observed that the difference between the two views had become largely verbal; in retrospect we might say, not verbal, but social and historical. The gap between the continuous change in ideas and the contemporary feeling of sharply discontnuous change is a measure of the elusive but real social and historical implications of the zymase debate, of the demise of an old establishment, and the emergence of a new.In retrospect, then, it is clear that a trend was already under way in various quarters when zymase appeared. But it was still a collection of isolated and dispersed events. The zymase controversy made the trend visible and gave it a dramatic unity. The debate influenced those who had already begun to change. It was so effective because things had begun to change and because it coincided with the direction of that trend. (shrink)