From Friedrich Wöhler’s Urine to Eduard Buchner’s Alcohol

A reading of Buchner’s first paper on cell-free alcoholic fermentation, reproduced in English on pp. 25–31 of the present book, reveals decided and fascinating residues of vitalist thinking, a strong reminder of the victory of custom over the dictates of observation. Thus one finds an interesting confusion between the view (p. 27) of zymase, the sugar-fermenting enzyme, as a dissolved substance, undoubtedly a protein, and the view (p. 28) of zymase as a genuine protein... much closer than invertin [Berthelot’s enzyme] to the living protoplasm of yeast cells. More interesting is the acceptance by Buchner of a fundamental difference between zymase and the established list of enzymes (p. 27), all of which merely bring about hydrolyses that can be imitated by the simplest chemical means (p. 28), an idea fortified or suggested by the inability, in contrast to observations with invertin, to maintain zymase activity upon precipitation with alcohol (p. 28). Mention is made of Baeyer’s ideas of alcoholic fermentation as a chemical process, but an air of mystery is allowed to remain about the possible chemistry of the fermenting process, perhaps unexpected from a person with a rigorous training in chemistry. In spite of Buchner’s realization that his results overthrew Pasteur’s dominant view on fermentation [We all grew up in the atmosphere of Pasteur’s views... I hence understandably was very sceptical when I... obtained experimental facts that appeared to indicate cell-free fermentation (Buchner, 1898)], it is clear that residues of the attitude that informed this view remained, but not for long: in his Nobel Lecture [This lecture, on 14 March 1898 before the German Chemical Society in Berlin, is quoted at greater length in the chapter by Bohley and Fröhlich (pp. 54–55)], Buchner discusses at length various chemical means, studied in several laboratories, to convert glucose to carbon dioxide and alcohol (Buchner, 1907, p. 116). In fact, Buchner was closer to the actual process of glycolysis than is generally realized. It is well known that Aleksandr Nikolaevich Lebedev’s method of using air-dried yeast as a ready source of zymase displaced Buchner’s method (Shamin, 1990, cf. Harden, 1932, pp. 24–26). What is much less well known is that Lebedev worked in Buchner’s laboratory in 1907, and there began his lengthy research on the chemical nature of alcohol fermentation, leading in 1909 to the first scheme of alcohol fermentation (Shamin, 1990), with the main role played by glyceraldehyde and dihydroxyacetone, and leading three years later to the corresponding phosphates. Thus this work provided a direct connection to the later work of Gustav Embden and of Otto Meyerhof. Although Lebedev had left Buchner’s laboratory by 1909, there is no doubt that it is there that the seeds for his work were planted.

Buchner’s results were attacked from various sides, but within a few years they were almost universally accepted (see Kohler, 1972; Fruton, 1972, p. 86). A highly amusing rejection was by a certain J. Reynolds Green, ScD, FRS, who already in 1897 dismissed Buchner’s work: For the present... I must contend, in opposition to Buchner, that at any rate our English Yeasts do not contain any alcohol-producing enzyme (Green, 1897). He later became a strong defender of Buchner’s views (Green, 1898). Another powerful acceptance came from Max Delbrück, the influential head of the Institute for Brewery Research and Teaching (Versuchs- und Lehranstalt für Brauerei) in Berlin (uncle of the future Nobel Laureate), after an initial rejection. He calls zymase the enzyme par excellence, justly called zymase, a sentiment not perhaps surprising from someone whose interests were centred in brewing. It is most interesting that the first public acceptance of Buchner’s work came already in 1897 from none other than Pierre Émile Duclaux, Pasteur’s first biographer, his immediate successor as director of the Pasteur Institute in Paris, and founder as well as editor of the influential Annales de l’Institut Pasteur. One would have expected the new findings to be opposed by a disciple of Pasteur, since they could be readily interpreted to conflict with the views of the recently deceased (1895) Pasteur. However, Duclaux’s respect for experimental observation, similar to Pasteur’s, prevailed, and he did not feel that Buchner’s findings contradicted Pasteur’s position. He wrote in the Annales in one of several 1897 papers championing Buchner’s work (see Kohler, 1972, p. 338):

Some scientists fully accept this discovery and even derive extreme conclusions from it by pretending that it overturns Pasteur’s doctrine on fermentations. Pasteur’s doctrine will be overturned the day that alcoholic fermentation will be achieved purely chemically and without any vital activity. But as long as yeast is needed to produce alcoholic diastase, Pasteur’s theory can express what the master himself would have said: Here is yet another vital activity [action vitale] which is manifested by a chemical mechanism.

DUCLAUX (1897, p. 348, my translation)

This position resembles that taken already in 1858 by Moritz Traube (Traube, 1858). A year later another former close Pasteur associate, Émile Roux, made a statement similar to Duclaux’s but the emphasis is rather more chemical:

Certainly, the decomposition of sugar by alcoholase is a purely chemical reaction, but the formation of the enzyme is an act associated with life, and since it is not yet possible to make alcoholase without a living cell it follows that alcoholic fermentation remains correlated with the life of the yeast.

ROUX (1898, p. 839, my translation)

Buchner’s own position vis-à-vis Pasteur was very modest:

The famous Frenchman’s theory consists of a physiological part: fermentation is life without oxygen, that is, fermentative organisms obtain their reservoir of energy by the process of fermentation, while the other living beings obtain it by means of respiration; and the theory consists of a fermentative-chemical half: no fermentation without organisms. The first statement is not at all changed by the discovery of zymase; the second statement requires only one modification: no fermentation without zymase, which his formed in organisms.

BUCHNER and RAPP (1898, p. 211, my translation).

Perhaps Bernal (1954, ch. 9, sect. 5) put it most succinctly:

In the end both von Liebig and Pasteur were right. Fermentation is brought about by a ferment, but that ferment can only be elaborated by a living organism.

However it is important to stress that the view of Duclaux and Roux were not shared by all scientists. Many still argued that yeast extract contained living protein or bits of protoplasm (see Fruton, 1972, p. 86). Kohler makes the important point that Buchner’s proof of the chemical view did not seem so unambiguous at first. Biologists’ reactions to zymase correlate very closely with their previous disciplinary commitments (Kohler, 1975, p. 295). Initially, at least, zymase was less a determinant of opinion than a touchstone of pre-existing opinion... The primary effect of the zymase debate... was on those who were already inclined to the new view (Kohler, 1972, pp. 351–352). In the long run it was time, not argument, that prevailed over fashion. Conceptual change came about not by wholesale conversions of individuals but by a process akin to natural selection, whereby the composite character of a population changes (Kohler, 1975, p. 295). The zymase debate occupied Buchner until his last papers.

We have here and there indicated that the sway of vitalist ideas did not meet universal acceptance in the 19th century. We mentioned Georg Sigwart, Marcellin Berthelot and Moritz Traube, Felix Hoppe-Seyler. One has to bear in mind that the narrow specialities with which we classify modern scientists did not hold sway in the 19th century, but it is of interest that groups of scientists whose primary concerns were not specifically chemical also tended to reject vitalist attitudes in favour of chemical or physicochemical ones. Thus already around 1847 a quadrumvirate of rising physiologists — Emil du Bois-Reymond, Ernst Brücke, Hermann von Helmholtz, and Karl Ludwig — decided to reject any explanation of life which appealed to nonphysical vital properties or forces (Turner, 1972). In the words of du Bois-Reymond, Brücke and I have sworn to each other to validate the basic truth that in an organism no other forces have any effect than the common physicochemical ones... (quoted by Lesky, 1973). The physiologist du Bois-Reymond vigorously opposed the introduction of physiological explanations in terms of a vital force. That force provided no explanation and was

but a comfortable resting place where... reason finds peace in the cushion of obscure qualities... If one observes the development of our science he cannot fail to note how the vital force daily shrinks to a more confirmed realm of phenomena, how new areas are increasingly brought under the dominion of physical and chemical forces... It cannot fail that physiology, giving up her special interests, will one day be absorbed into the great unity of the physical sciences; [physiology] will in fact dissolve into organic physics and chemistry.

quoted by TRUSTED (1996, pp. 118, 151).

An interesting case is that of Theodor Schwann. While Eduard Buchner in his book has a quotation (p. 48) from Max Delbrück (1898) that indicates Schwann to have been a vitalist, a revealing passage by Schwann (1878) à propos the vital force is quoted by Marcel Florkin (1975):

A simple force different from matter, as it is supposed, the vital force would form the organism in the same way as an architect constructs a building according to a plan, but a plan of which he is not conscious. Furthermore, it would give to all our tissues that which is called their proper energy, that is, the properties that distinguish living tissues from dead tissues: muscles would owe it their contractility, nerves their irritability, glands their secretory function. Here, in a word, is the doctrine of the vitalist school... I have... always rejected as illusory the explanation of vital phenomena as conceived by the Vitalist school. I laid down as a principle that these phenomena must be explained in the same way as those of inert nature.

Rudolf Virchow, the most prominent German physician of the 19th century (Risse, 1976), was very concerned with questions of vitalism. He wrote a book with the title Alter und Neuer Vitalismus (Old and New Vitalism) (Virchow, 1856) and is credited with the promulgation of a so-called neovitalism. In 1849 he decided to accept a special vital principle whose centre was the living cell. On the other hand, almost fifty years later, in a lengthy lecture given (in English) at the age of 77 in London on the occasion of the opening of the Charing Cross Hospital Medical School, we find the following:

How can a single power, whether we call it in the spiritualistic sense spirit, soul, spiritus rector, or, in the physical sense, vital force or electricity, build up... diverse organisms?... Cells are composed of organic chemical substances, which are not themselves alive, but the mechanical arrangement of which determines the direction and power of their activity.

VIRCHOW (1898)

On the other hand, one here also finds the following statement, which could have been written by Claude Bernard forty years earlier:

These two kinds of substances, the living and the non-living, cannot be identified with one another. In spite of chemical similarity or even correspondence, they exhibit recognizable differences, not alone physiological, but also mechanical and physical.

In the words of Diepgen (1952, quoted in Selberg and Hamm, 1993; my translation):

Virchow attacked the difficult problem [of vitalism] with the whole universality of his scientific and philosophical approach. All of cosmology, geology and paleontology, Newtonian physics, chemistry, especially ferment chemistry and catalytic phenomena, and especially the new observations in biology were included in the range of his proofs. On this basis the force that acts in the organism, and especially in the cell becomes for him a mechanistic and uniform vital force which is bound to matter.

Posner (1921) discusses Virchow’s attempts to reconcile his early purely mechanistic, i.e. physical or chemical, view of vital phenomena with his later ideas on a special vital force, and concludes: It is scarcely possible to say that he penetrates [this matter] with complete clarity (my translation). The correspondence, extending over a period of thirty years (1864–1894), between Virchow and du Bois-Reymond which among many topics touches the above, has recently been published with an illuminating editorial introduction (Wenig, 1995). Virchow’s fluctuations between acceptance and rejection of a vital principle can be regarded as symptomatic or representative of the 19th century fascination with this topic, its divisiveness and its uncertainty.

Paradoxically, it was precisely in the area of biological research closest to chemistry, areas that we would now call biochemical, as exemplified by the Pasteur–Berthelot altercation, that the vitalist, non-vitalist debate held centre stage, and it is therefore perhaps not too surprising that it is precisely here that a decisive observation had by far the greatest impact. So, from the viewpoint of Buchner’s work, his experiment struck home, as it were, far more strongly than the generally proclaimed views of principles and attitudes that one way or the other failed to convince the majority, because of a mixture of attitude and the lack of decisive observations.

The experimental results that follow from the physicochemical approach to living processes are due not only to properties intrinsic to the phenomena selected for study but also to the operation of the selection process itself. The physicochemical approach has been singularly successful because, in Victor Henri’s words (1903), it can be analysed experimentally and hence can permit a deeper understanding of the mechanism of the phenomena studied. This deeper understanding is made possible not only in terms of the physicochemical results by themselves but in terms of their wider implications. The physicochemical approach, which has been so productive in the inanimate world, has now become the stock-in-trade not only of the biochemist’s but also of the biologist’s study of living systems. This approach continues to encroach on domains of biological thinking from which it had originally been deliberately excluded.