Friedrich Miescher and his discovery of nuclein

Friedrich Miescher (1844–95) was born in Basel, Switzerland, into a family of medical scientists. His father Friedrich Miescher (1811–87), after whom he was named, was a practising physician who taught pathology at the University of Basel and conducted investigations on bone inflammation; and Wilhelm His (1831–1904), the renowned anatomist and pioneering neuro-embryologist, was his uncle.Footnote ⁴ The younger Miescher first studied medicine at the University of Basel and even specialized in otology, but due to hearing problems of his own – which would have impaired his ability to perform such basic medical duties as using a stethoscope – chose not to be a physician. Instead, acting on the advice of his uncle, Miescher enrolled at the University of Tübingen in 1868 to study the field then known as physiological chemistry. As His later recounted,

Miescher spent his first several months in Tübingen learning the techniques of organic chemistry in the laboratory of Adolf Strecker (1822–71) before joining the laboratory of Felix Hoppe-Seyler (1825–95), one of the pioneers of physiological chemistry in Europe. Best known for his groundbreaking work on the nature of haemoglobin, a name that he coined for it, Hoppe-Seyler steered Miescher towards white blood cells as the source of material for studies on the chemical composition of blood, thus setting him, fortuitously, albeit not intentionally, on his path to the discovery of DNA.Footnote ⁶

At first, Miescher attempted to obtain lymphocytes as the primary material for his studies, but he was unable to isolate them in the quantity and purity that he needed. A resourceful young scientist, he cast about for other sources and soon found that pus – which could be obtained by washing surgical bandages, of which there was a ready supply from a nearby surgical clinic – was a rich source of other types of white blood cells (leucocytes) that he could purify and analyse further. Although extracting intact pus cells from the bandages was a far from easy task – as Miescher made evident in the eloquent descriptions of his work that he provided in his copious letters to his familyFootnote ⁷ – he was nevertheless able to obtain sufficient quantities of purified pus cells to pursue investigations of their chemical composition.

Following a brief introduction in which Miescher explains his motivations for pursuing the study of pus cells, delineates the scope of his analysis – specifying that he will focus on intact pus cells only and not examine other pus components – and describes the experimental material and the preliminary preparation before analysis, the paper is divided into five sections. Uneven in length, these sections follow the progression of the chemical analysis, describing in turn: the proteins of the protoplasm – what today would be labelled the cytoplasm (pp. 443–8); the alcohol-soluble portion of these protoplasmic contents (pp. 448–50); the aqueous portion of the extract (a single paragraph on p. 450); the ash or residue of combustion of the protoplasmic material (pp. 450–2); and, in the final and longest section, the nuclear contents (pp. 452–60). Although Miescher did not offer his rationale for such an unevenly weighted discussion of the different stages of extraction, it would appear that chance, in terms of both timing and opportunity, and an existing lacuna in the state of knowledge of cellular chemistry at the time, all played roles in directing his investigative focus.

First, his choice of raw material was fortuitous. Compared to normal cells, leucocytes in pus have a large ratio of nuclear material relative to the total cell, the result, as we know now, of their active proliferation when they gather at the site of any wound during the healing process.Footnote ⁸ Consequently, Miescher was able, even in his preliminary analyses, to separate intact nuclei from the rest of the protoplasm quite easily, which gave him the opportunity to analyse their contents. It was in the course of these experiments – details of which we will leave readers to discover directly from his paper – that Miescher discovered a nitrogen- and phosphorus-rich substance localized in the nuclei. Concluding on the basis of his analysis that this substance was distinct from proteins, which were the most common nitrogenous substances present in living cells, he introduced for it, without fanfare, in the paper's final section, an entirely new label – nuclein – (Miescher 1871, p. 452). Following a detailed account of the chemical analysis of the nuclear fraction, he also mentioned, almost in passing toward the very end, the potential significance of nuclein, suggesting that it comprised a group of biological substances that would prove to be as important as the proteins (Miescher 1871, p. 459).

Miescher completed his experiments in Tübingen by August 1869, and wrote up and submitted his paper to Hoppe-Seyler in December that year: ‘If Hoppe does not refuse it, then I have taken the first step towards publication’, he wrote to tell his parents.Footnote ⁹ While his former mentor did not refuse it outright, he did not react to it positively either; in fact, he did not respond at all for a couple of months, leaving Miescher to wonder worriedly in a later letter, ‘I have become doubtful whether the work that I sent to Hoppe arrived at its address as I have received no signs of life from Tübingen. I have therefore written again to Hoppe’.Footnote ¹⁰

It was only after receiving this second letter that Hoppe-Seyler wrote back to Miescher, and even then, without the unqualified good news that the latter had doubtless hoped for:

Hoppe-Seyler not only repeated Miescher’s experiments himself, he also assigned further investigation of the problem to another one of his students, Pal Plósz (1844–1902). The latter found that nuclein was present in the blood cells (RBCs) of birds and snakes – both of which have nucleated RBCs – but not in bovine RBCs, which, like those in humans, lack nuclei. Taken together, these results convinced Hoppe-Seyler of Miescher’s claims that nuclein was indeed a new category of cellular material, distinct not only from proteins, but also from lipids and carbohydrates, and located specifically in the nuclei of cells. He therefore published Miescher's 1869 paper together with his own and Plósz’s papers in the 1871 issue of his institute's journal Medizinisch-chemische Untersuchungen.Footnote ¹² The issue also featured a second paper by Miescher reporting the presence of nuclein in the yolks of eggs from domestic hens, although later investigators seemed to think that the bulk of the phosphorus in this case came from lecithin.Footnote ¹³

In the introduction of his own paper Hoppe-Seyler freely admitted his own initial scepticism about the validity of Miescher's findings and conclusions especially in light of their ‘great physiological importance’ and implications for understanding the chemistry of cells. One of his biggest reservations about Miescher's conclusion that nuclein was an entirely new class of biological substance had been that nuclein could have been a ‘type of peptone produced by the prolonged effect of gastric juices on the protein substances in the nucleus’.Footnote ¹⁴

There was a precedent for such a possibility, one that Hoppe-Seyler had good reason to be cautious about. As he noted in his paper, ‘Through the prolonged digestion of casein from milk by digestive gastric juice, Lubavin obtained a very similar substance’, which had turned out to be the products of protein degradation after all.Footnote ¹⁵ But further experiments comparing the results of his chemical analysis of protein degradation against both Lubavin and Miescher's results led Hoppe-Seyler to concede that ‘the nucleus contains a material with the composition and qualities described by Miescher, especially the remarkable phosphorus content, that is not simply produced as an artefact of digestion’.Footnote ¹⁶ Consequently he acknowledged, ‘When I turn to describing the results of these investigations, I can only emphasize that, insofar as I have checked Miescher's information, they must be considered as being fully confirmed’.Footnote ¹⁷

Miescher, who had moved away from Tübingen soon after completing his experiments – first for one year of further training with the German physiologist Carl Ludwig (1816–95) at Leipzig, and then in 1871 back to his home town to take up a professorship of physiology at Basel University – retained his interest in nuclein to the end of his life. Although it was not his primary pursuit while at Leipzig, he lost no time in resuming his research once he had established his laboratory in Basel. But these later studies did not involve pus cells; by then he had found a far richer and more easily obtainable source of nuclein – the sperm cells of salmon, of which he was assured a steady and abundant supply due to Basel's thriving fish industry. With this material he went on to conduct the type of detailed analysis that, as he noted in his first paper, he had been unable to perform due to the paucity of material (Miescher 1871 pp. 442, 458, 460). These experiments further convinced him of the importance of nuclein – which, based on their acidic properties, were renamed later as the nucleic acids in 1889 by his pupil Richard AltmannFootnote ¹⁸ – ideas that had only been hinted at in his first paper (pp. 459–60). Perhaps because of the overwhelming dominance of the nuclei – and hence nuclein – in sperm cells, he would go as far as to speculate that if one wanted to assign the specific cause of fertilization to a single substance in the cell, then ‘one should undoubtedly first and foremost consider nuclein’.Footnote ¹⁹

Contextualizing Miescher's research and reception

In order to gain some understanding of both the significance and the reception of Miescher's discovery, it is necessary to consider the intellectual climate prevailing in Europe in the mid-nineteenth century, in particular the status of research on the cell. The discovery of cells is generally attributed to Robert Hooke (1635–1703), who was responsible for introducing this term into biology in his 1665 book Micrographia.Footnote ²⁰ But the modern idea of the cell as the fundamental unit of life – what is known as the ‘cell theory’ – was not formulated until the 1830s by German botanist Matthias Jakob Schleiden (1804–81) and zoologist and physiologist Theodor Schwann (1810–82), just a few decades before Miescher embarked on his investigations.Footnote ²¹ Schleiden, Schwann and other cytologists who succeeded in their wake – for example, Rudolf Virchow (1821–1902) and Ernst Haeckel (1834–1919) – were primarily interested in the form and structure of cells, and the origin and multiplication of their components.Footnote ²² Their interests and investigative approaches were quite removed from those of the physiological chemists such as His, Hoppe-Seyler and Miescher, who were more interested in showing that the complexity of the cell could be reduced to a chemical understanding. This attitude is well exemplified in Miescher's various letters to His; on at least one occasion he referred to the cytologists dismissively as ‘the guild of dyers’, and while he conceded that microscopic studies needed to go ‘hand in hand’ with the kind of chemical analyses that he was performing, he firmly believed that microscopy alone had serious shortcomings.Footnote ²³ In an unpublished follow-up to his first report, he expressed his confidence that chemical studies of the kind he had performed on nuclein would ‘bring an understanding of the meaning of histological structural elements that is currently so distant, one step closer. The understanding of the nucleus will be freed from superficialities such as form, size, opacity, solubility relationships, which are permitted by mere conclusions from analogy’.Footnote ²⁴

As for the nucleus, although its existence had been known for decades, the early cytologists had by and large ignored its significance for cellular function. True, Haeckel was one of the first people to propose, in his classic Generelle Morphologie der Organismen (1866), that cellular activities were specific to different compartments: heredity to the nucleus and adaptation of the cell to its surroundings to the protoplasm.Footnote ²⁵ But not being a chemist, he did not conduct the detailed analyses of the type that Miescher would perform a few year later. Instead, he concluded that both protoplasm and cytoplasm contained proteins, distinguishable from one another by just ‘small physicochemical differences’.Footnote ²⁶ Whether or not Miescher knew of these ideas at the time he conducted his own analysis is doubtful. Certainly, he did not cite Haeckel's work in his papers, as he did, for instance, the contradictory evidence of other physiological chemists of his time. Relying on his own intuition and judgement, he went on to show that the physicochemical differences between the protoplasmic and nuclear substances were fundamental.

What of the reception of Miescher's finding by his contemporaries? Despite Hoppe-Seyler's corroboration and endorsement and the positive reception from other physiological chemists, including his later mentor, Carl Ludwig, his paper does not seem to have ever received the type of recognition that the other breakthroughs contemporary to his own discovery have enjoyed. The aforementioned works of Darwin and Mendel are but two examples; there are others from that period – Theodor Boveri, Walther Flemming, Ernst Haeckel and Edmund B. Wilson – whose seminal contributions toward the study of cells both were well known then and are recognized even today.Footnote ²⁷ In today's predominantly anglophone academic culture, which has lamentably excluded scholarship in other languages except in small localized pockets, it is tempting to attribute the relative obscurity of Miescher's paper to language. But this linguistic explanation does not hold water for Miescher's own times, when German and French were the official scholarly languages in the West and it was not unusual for European and English scholars at least to be familiar with the contemporary literature of their disciplines in multiple languages. Indeed, with the exception of Darwin and Wilson, none of the other scientists mentioned above wrote their papers in English. Yet Boveri, Flemming and Haeckel were well known by their anglophone contemporaries, and their work and contributions cited enough for them to have become part of the canon not only of science but of history of science as well. His mentors’ good opinions notwithstanding, Miescher's discoveries evidently did not attract the same sort of widespread attention even in his own times.

The very title of the paper, ‘On the chemical composition of pus cells’, may hold some clues about the relative lack of attention to this paper by those historians of molecular biology and genetics most likely to be interested in the discovery of DNA, or even of the history of biological chemistry. First, it says nothing whatsoever about DNA or even the nucleic acids more broadly. Such an omission is not surprising since these terms were not yet in existence and, indeed, their coinage depended on the very discoveries reported in the paper. Even nuclein is not mentioned in the title; in fact it does not make its first appearance until the title to the concluding section of the paper: ‘The nucleus and nuclein’. Consequently, the paper is unlikely to be flagged in a search for sources using the standard keywords one might consider when embarking on a project about DNA, its origins, its role in genetics or, for that matter, the history of its chemistry. Certainly it is unlikely that novice researchers would use the word ‘pus’ as a keyword in their search for literature on DNA. Pus is a substance most commonly associated with wounds and infections, and there is no reason to single out a paper about the composition of its cells over that of a paper on any other type of cell. Almost all cells contain DNA, after all! Indeed, thanks to modern companies such as 23 and Me, or geneaology.com, historians interested in DNA and such are more likely to notice papers mentioning cheek scrapings or saliva than those about pus.

Another reason for the frequent oversight of this paper by historians might well be that Miescher used the relatively vague language of conjecture and possibilities in describing the little information he gave about any property of nuclein other than its chemistry. He made a very brief mention about the possible physiological function of phosphorus – and therefore, by implication, the phosphorus-rich nuclein – in the growth of actively multiplying cells, but set aside the matter for future experiments (Miescher 1871, p. 459). In fact he wrote a follow-up paper addressing the physiological significance of nuclein which he submitted to Hoppe-Seyler during the time he was waiting for a verdict on his first report.Footnote ²⁸ But despite his own positive remarks – in his introduction to Miescher's first paper he suggested that nuclein might ‘play a very important role in the development of all cells’ – Hoppe-Seyler did not publish it.Footnote ²⁹ Miescher, too, does not appear to have pursued this matter, and in later years returned to the topic only briefly, possibly because his real interest at that time lay not so much in elucidating the function of nuclein, but rather in how its study might elevate the status of physiological chemistry as an emerging discipline.Footnote ³⁰

Finally, it is also instructive to compare certain aspects of Miescher's and Mendel's publications for they share some of the main features suggested above for their relatively poor reception. Both, for instance, have rather nondescript titles, neither hybridization nor peas being any more compelling than chemical analyses and pus. And yet, as we know, Mendel's paper, after an initial period of obscurity, was rediscovered at the turn of the century, after which it never lost its traction.Footnote ³¹ Various scholars have suggested that one major reason for this turn in the early twentieth century was economic; the drive to industrialize agriculture led to an interest in hybridization, and hence a promotion of Mendel's work.Footnote ³² Despite its importance in medicine, however, physiological chemistry did not show a similar expansion in the early twentieth century.

The continued popularity and relevance of Mendel's paper since its first discovery is certainly borne out by the fact that it has been translated multiple times into English since 1900. The first known published translation was initiated by the English biologist William Bateson, who commissioned Charles T. Druery (1843–1917), a poet and expert on British ferns, to undertake the task.Footnote ³³ One of the most recent, by Staffan Müller-Wille and Kersten Hall, was part of the present BJHS translation series.Footnote ³⁴ In contrast, although various scholars – especially but not exclusively Ralf Dahm – have provided translations of passages from Miescher's work in their writings about him, a translation of his entire paper into English has not been available until now.

Toward the end of his life, cut unfortunately short due to a protracted battle with tuberculosis, Miescher received a sympathetic letter from his former mentor, Carl Ludwig, commiserating with him on his illness:

It is our hope that making Miescher's entire paper available to a wider audience than before will open up many questions and issues for discussion among scholars from multiple disciplines, and further the truth of Ludwig's words for several more generations to come.

Translators's note

Any translation is a work of interpretation, and embeds within it a certain amount of the translators’ perspective and biases. Ours is no different. As our main intent in undertaking this task was to make Miescher's original paper available and accessible to current and future generations of anglophone scholars, we have used modern (i.e. twenty-first-century) English in our translation. At the same time, however, we have attempted to be true to Miescher's times and thus avoided anachronistic terminology, which would not have existed in his times. Where necessary we have provided explanatory notes to offer some context and background that Miescher himself did not need to provide. Another feature to which we draw attention is a certain lack of consistency and unpredictability in Miescher's use of full names versus symbols or formulae for different chemical substances. We have used the full form of each material in our translation, but feel we must identify two specific examples which may be unfamiliar to modern readers either because they are now obsolete or because the usage is non-standard. The first is ‘ether’, for which Miescher used the notation Ā in six instances (pp. 446, 447 (twice), 453, 456, 457), although he used the full form (Aether in German) at least as many times as well. The second example is the use of the abbreviation ‘Pt.’ (period inclusive) in his reports of his chemical analyses of various cellular components (see p. 457). The notation Pt, minus the period, is the chemical symbol for the element platinum, but it is clear, based on the reported quantities of the substance, that Miescher could not have been referring to platinum. Based on the context, our best guess is that Miescher was using it as a shorthand for ‘precipitate’.