1. The primary substance

Scientific claims can leave a cultural imprint which lasts long after expert consensus has moved on.¹³ This pattern will prove important in understanding several episodes in the history of protein, not least the story of its ‘discovery’.

The word protein (more specifically Protéin) was first used in a publications by Dutch chemist Gerrit Mulder in 1838.¹⁴ Mulder had been working on the elemental compositions of various organic substances believed to be major constituents of animal tissues (fibrine, gelatine, egg albumen) as well as similar substances found in plants. These all contained nitrogen, carbon, oxygen and hydrogen—but since it was the presence of nitrogen that distinguished them from other plant and animal substances, they were often referred to as the ‘nitrogenous substances’. Mulder had discovered that the proportions of these component elements in all these substances were nearly identical; by this measure, the nitrogenous substances differed from each other only in very small quantities of phosphorus and sulphur. He hypothesised, reasonably enough, that they were in fact all the same compound: he envisaged a radical¹⁵ produced by plants, consumed by animals and passed up the food chain, being modified only slightly in each body. This hypothetical substance he named protein, and claimed it was possible to remove the phosphorus and sulphur from any of the nitrogenous substances and so create pure protein.

This choice of name was significant. Letters from the time show that the idea had come from the far more famous chemist Jöns Jacob Berzelius.¹⁶ Writing to Mulder, Berzelius explained that he had derived the word protéine from Greek—but the details are a little confused. Authors in the following decades gave different accounts, mentioning several related Greek words meaning ‘good quality, best’¹⁷, ‘supremacy, first prize’¹⁸, ‘take first prize, hold supremacy, be first’¹⁹ and simply ‘first’²⁰. It is not entirely clear from Mulder and Berzelius’ writings which of these words they had in mind²¹ and which particular meaning they intended to invoke—Mulder himself usually referred to the Latin word primarius in explanation. The logic could have been that this was “the first nutrient in the food chain”, or “the highest quality foodstuff”, or “the food of the foremost people” or “the most important component of food”. Instead of a clear explanatory story, the etymology offered a cloud of connotative links between the new word protein and notions of firstness, quality, primacy and supremacy.²²

This idea of a single substance which underlay the food chain and was the building block of all animal tissues came to be called ‘protein theory’. It was, however, short lived. The theory was briefly taken up by celebrity scientist Justus von Liebig, who claimed in his response to Mulder to have reproduced his results and created pure protein in the lab.²³ Liebig and his graduate students focused intensely on protein theory from 1838 onwards so that it could be included and elaborated upon in Liebig’s Animal Chemistry (1842).²⁴ Where Mulder’s papers had presented a hypothesis, Liebig’s book offered settled scientific facts: ‘proteine’ was a single compound, synthesised in plants, consumed by herbivores and passed up the food chain; it was carried throughout the body by blood, where all other animal tissues (generally compounds of proteine with small quantities of phosphates, other salts, sulphur and phosphorus) were produced.

For a short period, protein theory was popular—but Liebig received a mixed response to Animal Chemistry, and became embroiled in a bitter conflict with Berzelius over criticisms of it.²⁵ Liebig’s initial optimism about removing the ‘impurities’ from albumen, fibrine and caseine and so creating ‘pure protein’—the experimental proof that the theory needed—faltered as his students failed to make progress.²⁶ He went on to claim that Mulder had misled him and by 1847 was attacking both the theory and its originator in no uncertain terms, saying that “Mulder’s theory of proteine is fallacious”, that “proteine does not exist”, and that “so-called proteine theory” should not even be regarded as a scientific theory.²⁷ This resulted in an angry exchange of public recriminations with Mulder of a kind that punctuated the whole of Liebig’s scientific career.

For the following three decades, protein theory remained contentious and most writers in English returned to using terms like ‘albuminoids’, ‘albuminous substances’ or ‘nitrogenous substances’ as a shorthand for albumin, fibrin, casein and so on.^{28 29} The word protein and its variants (proteine, protein-bodies, proteinous substances, proteid; German Proteine, French protéine) continued to crop up in texts on organic chemistry, generally when making reference to protein theory,³⁰ alongside occasional use as a synonym for ‘nitrogenous substances’ or ‘albuminous substances’.³¹ We also find instances of protein being used as a term for the ‘nutritive’ (nitrogen- containing) component of crops.³² Since protein remained a relatively unusual, technical term, many of these authors felt it necessary to introduce it in some way — typically by making reference to Mulder and offering some version of the etymological story. In this way, even though Mulder’s theory never gained any lasting acceptance, a set of impressionistic associations between the word protein and firstness, quality and supremacy were firmly established.

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