Hopkins, Frederick Gowland

(b. Eastbourne, Sussex, England, 20 June 1861; d. Cambridge, England, 16 May 1947)

biochemistry.

Hopkins was not only the father of British biochemistry but also a major contributor to biochemical thought and to experimental biochemistry throughout the world. Quiet, kindly, and mild, he had the greatest tenacity and forcefulness of character when facing challenge or opposition to the ideas in which he believed. No one was more firmly opposed than he to the vitalist thinking of many of his contemporaries and to the obscurantist attitude to which this thinking gives rise. For him the nature of protoplasm was not insolubly mysterious but something accessible to the experimental approach, something inherently comprehensible. “The use of the term protoplasm may be morphologically justified,” he wrote on one occasion, “but chemically it denotes an abstraction.”

His own views were perhaps most sharply crystallized in Hopkins’ presidential address to the Physiology Section of the British Association for the Advancement of Science, delivered at Birmingham in 1913:

In the study of the intermediate processes of metabolism, we have to deal, not with complex substances which elude ordinary chemical methods, but with simple substances undergoing comprehensible reactions.... It is not alone with the separation and identification of products from the animal that our present studies deal; but with their reactions in the body; with the dynamic side of biochemistry.

Hopkins was less concerned, except as an article of his own particular biochemical faith, with the question of whether the application of chemical methods can ultimately provide complete answers to biological problems, for that was—and still is—a problem for the future to resolve. But that biochemistry can provide significant new information on problems of this kind—had this not been clear enough from Hopkins’ own work—has in the meantime become sufficiently evident to justify every article of the biochemical faith in which he so strongly believed and which he lost no opportunity to impress upon others. It was characteristic of Hopkins’ department that one thought and talked in terms of dynamic events rather than of mere structure. Such an atmosphere was inevitable because, for Hopkins, “Life is a dynamic equilibrium in a polyphasic system.”

Hopkins entered biochemistry at an early stage in its development, although comparatively late in his own lifetime. At school he showed no remarkable distinction except in chemistry, but he was fascinated by a microscope that had belonged to his father. “I felt in my bones,” he once wrote, “that the powers of the microscope thus revealed to me were something very important—the most important thing I had as yet come up against; so much more significant than anything I was being taught at school.” Together with an evident aptitude for chemistry, this microscope must have done much to determine his eventual scientific development.

He was brought up by his widowed mother and an unmarried uncle who, when Hopkins was seventeen, chose for him a career in the London office of a provincial insurance company. From this post he was rescued after six months by his father’s cousin, Fritz Abel, who, in Hopkins’ own words, “at once said ‘Cambridge.”’ But it was not until twenty years later that this goal was achieved.

During the intervening years he was trained as an analyst, in which capacity he worked for one of the larger railway companies and obtained his first professional qualification, the associateship of the Institute of Chemistry. He distinguished himself in the examination and was thereupon invited to become an assistant to Thomas Stevenson, expert medical jurist to the Home Office. In this capacity he became involved in several celebrated murder cases, notably those of Bartlett, Lipski, and Maybrick. In several of these his analytical skill played a large part in securing convictions.

By this time Hopkins was more conscious than ever of his need for more formal training and a university degree, which he sought and obtained as an external student at the University of London. In 1888, at the age of twenty-seven, he received a small inheritance and decided to enter the medical school at Guy’s Hospital. In the course of this training he won the gold medal in chemistry and honors in materia medica—another hint of the direction he was ultimately to follow. After qualifying he worked for some years with Archibald Garrod, who became a lifelong friend and founded the then relatively new science of biochemical genetics. For a number of years Hopkins worked in the medical school by day and in a privately owned clinical research laboratory in the evenings. In September 1898, at the age of thirty-seven, he went to Cambridge at the invitation of Michael Foster, then professor of physiology.

Foster’s wish was that Hopkins should undertake the teaching and development of what was then known as chemical physiology, a task which at that time meant tutoring in physiology and anatomy as well. This sort of experience has bedeviled many new entrants to the older English universities, and in Hopkins’ case it led to a breakdown in 1910. Later he wrote:

My recovery was greatly helped by an event which I count as the most outstanding among my gifts from Fortune. I heard during my illness that Trinity College had made me a Fellow and elected me to a Praelectorship in Biochemistry.... So far as the College itself is concerned the post carries no obligations.... It is my hope that in any account of my career published after my departure the generosity of Trinity College will be emphasized.

Thus it was not until the age of almost fifty that Hopkins was able to devote the greater part of his time to the development of biochemistry in the university and to his own research, although, despite difficulties and financial embarrassments in the early years at Cambridge, he had already published some thirty papers—nearly a quarter of his research output.

Hopkins made a complete recovery from his illness. Two papers appeared in 1910, and in 1912 he published what is perhaps the best-known of his works: “Feeding Experiments Illustrating the Importance of Accessory Food Factors in Normal Dietaries.” Although it was known to Aristotle that raw liver can cure night blindness, and although Captain Cook was aware of the antiscorbutic properties of lime juice, it was only through Hopkins’ work that the existence of vitamins became firmly and finally established. The experiments that lay behind this fundamental demonstration were, like much else of his experimental work, masterpieces of design and ingenuity and became the model for nutritional experiments for many years to come. In 1913 came his brilliant address to the British Association for the Advancement of Science at Birmingham, of which Marjorie Stephenson wrote:

It is indeed a biochemical treatise in miniature and discloses fully and with amazing clarity Hopkins’s inmost thoughts and speculations on the biochemistry of the cell.... It shows Hopkins at the height of his powers reviewing biochemical work from the days of Liebig onwards and interpreting it so as to build up a picture of the cell as the seat of ordered chemical events controlled in the interests of growth and function.

This address, as important a landmark in the history of biochemistry as it was in Hopkins’ own intellectual development, can be read and reread today; it is in fact one that should be known by every aspiring young biochemist and, indeed, could still profitably be consulted by many of his senior colleagues.

In 1914 Hopkins became the first professor of biochemistry at Cambridge; the new department, destined to become a mecca for biochemists, was housed in makeshift accommodations until 1925. Throughout the war years he spent much time on government business, served on the Royal Society Food Committee, and became involved in many other scientific wartime activities—none of them military, for he abhorred war. Problems of food rationing and nutrition claimed much of his attention. Butter was scarce and expensive; margarine, cheap and more easily available. There was, however, considerable unease among its manufacturers regarding its nutritional value, an unease to which Hopkins’ own discovery of accessory food factors contributed much. In 1917 he agreed to carry out further nutritional research on behalf of and with the support of the margarine industry, but on the understanding that he must be free to publish his results. Margarine, it soon became clear, was much inferior to butter in nutritional value because it lacked “fat-soluble A.” (As Mellanby later showed, this factor has two components, now known as vitamins A and D.)

Hopkins took an active part in this work until 1920 and continued to act as a consultant to the industry for a number of years afterward. In the meantime J. C. Drummond carried out an extensive survey of natural sources of the A and D vitamins, and industrial research pushed ahead with investigations into the possibilities of introducing A and D into the commercial product. In 1926–1927 the first “vitaminized” margarines appeared in the shops, and by 1928 they had received the certificated approval of the Pharmaceutical Society. Vitamin-enriched margarine is now popular and the modern product is little, if at all, inferior to the best dairy butter from the viewpoint of calorific value and vitamin content.

After the war biochemistry became for the first time a subject for part II of the natural sciences tripos at Cambridge, and there began the great phase of expansion and development, at Cambridge in particular but in other universities as well, for which Hopkins had striven so long and so energetically. It was not until 1935 that Hopkins decided to introduce biochemistry as a subject in part I of the tripos, a decision that caused some misgivings at Cambridge and much criticism from other universities. But he was so convinced of the importance of the subject that he maintained that no student who wished to do so should be barred from studying the subject, at least on an elementary level. The innovation proved a popular and brilliant success, and elementary courses in biochemistry became widespread in English universities.

The rest of Hopkins’ career can easily be summed up as a steady march from distinction to distinction. He was knighted in 1925, awarded the Copley Medal of the Royal Society in 1926, shared the Nobel Prize in physiology or medicine with Eijkmann in 1929, became president of the Royal Society in 1931, and received that most prized of all civil distinctions, the Order of Merit, in 1935.

In addition there were numerous honorary degrees from universities throughout the world. Yet near the end of his autobiography, characteristically enough, Hopkins could only say:

My own temptation has been to try and show that it is not altogether my own fault if I have remained—what I feel myself to be, compared with many others who have received less recognition and fewer rewards—intellectually an amateur. I realise today that I know and have known no aspect of science au fond—I was led at a right moment to follow a path then trodden by very few and where every wayfarer was conspicuous.

Hopkins’ autobiography, begun ten years before his death but never completed, shows him still active in his research, still an inspiring teacher: a quiet, calm, affectionate professor in a department most members of which owed their own distinctions largely to his early inspiration and encouragement and who revered, respected, and admired him. It often happens that a brilliant research worker is indifferent as a teacher, and in Hopkins’ case elementary teaching was not his forte. Yet with the advanced classes he was superb, and his lectures were usually attended by the entire department. Often the lectures showed little sign of previous preparation—he seldom used notes in any form, instead choosing a theme that interested him at the moment and developing it as he went along. But he was best of all in discussion, formal or informal. Marjorie Stephenson wrote of him: “Never was he known to fail; by skilful suggestions and questions he turned the most unpromising material into something interesting and significant, leaving the author encouraged and sufficiently selfconfident to meet the most obvious criticisms of his colleagues.”

It seems likely that this success was due to Hopkins’ clear mental picture of the cell as a biochemical machine; and into this scheme he was able to fit what seemed to his colleagues to be mere isolated observations, thus giving them significance. This intuitive understanding of the nature of the cell appears to have been an early development in his thinking, and it played a major part in the inspiration and encouragement he gave to his pupils.

Unlike many Continental professors Hopkins did not try to build up a school in which every student would be put to work on one or another of the professor’s own problems. Any student with a worthwhile problem in mind was encouraged to follow his or her own line of thought and research, and Hopkins invariably made valuable ideas and suggestions. Frequently, having broken new ground, he would hand over even the most promising of fields to younger colleagues, many of whom later achieved much distinction through the pursuit of a line of work inherited from Hopkins.

Some idea of Hopkins’ contribution to the propagation and continuation of his subject may be gained from the fact that, by the time of his death, some seventy-five of his former students occupied professorial chairs in various parts of the world.

The earliest of Hopkins’ known publications (he did not himself possess a complete set of reprints or even a list of his papers) was written while he was still at school and concerned the habits of the bombardier beetle, Brachinus crepitans. His interest in insects led him to study the pigments of pierid butterflies. This interest remained with him and he returned to it toward the end of his life, following H. Wieland’s discovery that the white pigment is a member of the pterin group and not, as Hopkins had believed, uric acid.

Hopkins’ interest in uric acid was carried over into the early days of his medical research at Guy’s Hospital, and his earlier training as an analyst enabled him to develop a new and superior method for its determination in urine. Although now generally superseded by colorimetric and other methods, Hopkins’ procedure remained the most accurate and reliable for several decades. The effects of diet upon uric acid excretion aroused his interest in proteins and led to attempts to obtain crystalline preparations of these substances. Here again his analytical experience enabled him to improve greatly upon existing methods and to lay the foundations for new work.

Together with S. W. Cole, Hopkins went on to track down the substance responsible for the already wellknown Adamkiewicz reaction of proteins and thus was led to the isolation of the amino acid tryptophan. Again the analyst’s skill played a large part in devising procedures for its isolation. Determination of the structure of this new substance was carried out, and the action upon it by bacteria was investigated. This led in turn to the beginnings of bacterial biochemistry, pursued for a time by Marjorie Stephenson and Harold Raistrick. Subsequent developments, especially in the gifted hands of Marjorie Stephenson, are well-known and form a major branch of biochemical study today.

Several miscellaneous papers on proteins followed; and Hopkins’ interest then turned to nutritional studies, now that proteins could be obtained in a supposedly pure state, and he was quick to show that the newly discovered tryptophan is an indispensable dietary constituent. The nutritional roles of arginine and histidine were studied later, but in the meantime Hopkins had been much impressed by the inconsistency of the results of nutritional studies being carried out by other workers. By this time, he wrote, “I had come to the conclusion that there must be something in normal food which was not represented in a synthetic diet made up of pure protein, pure carbohydrate, fats and salts; and something the nature of which was unknown.”

Young rats fed on such diets failed to grow and even lost weight unless they were given small amounts of milk daily. Hopkins concluded that milk contains “accessory food factors,” which are required only in trace amounts but are indispensable for normal growth and maintenance. This led to the “vitamine hypothesis,” which, although based on a series of very elegant and eloquent experiments, was hotly contested for many years. Published in 1912, the results—or at any rate Hopkins’ conclusions—were still in dispute as late as 1920, although three years later most of the opposition had evaporated. For this contribution to the knowledge of nutrition he shared the 1929 Nobel Prize in physiology or medicine with Eijkmann.

Going back to the first decade of the century, we find the beginnings of yet other branches of modern biochemistry. Together with the physiologist Walter Fletcher, Hopkins undertook a series of investigations on muscle, one of the few investigations which did not directly follow the main lines of his work. It had hitherto been generally believed that the contraction of muscle is associated with the formation of lactic acid, but the evidence was more than a little unconvincing. Fletcher and Hopkins seem to have been the first to realize that all of the methods formerly used for the estimation of lactic acid involved stimulation of the muscle itself, so that as much lactic acid would be found in unstimulated controls as in stimulated muscles. It was therefore necessary to devise methods whereby lactic acid could be extracted and the amount measured without stimulation of the controls. This was achieved by using thin, small muscles, dropping them into ice-cold alcohol, and grinding the material rapidly, so that enzymatic activity was reduced to a minimum. This appears to have been the first time the necessity of stopping enzyme activity as a preliminary to chemical analysis of irritable or any other kind of tissue had been realized or even suspected.

In the hands of Fletcher and Hopkins the new technique yielded the first incontrovertible proof that muscle activity and lactic acid production are intimately associated; it led others—D. M. Needham in Hopkins’ own laboratory, for example—to the early growth and development of the detailed knowledge of muscle metabolism that we possess today.

The work on muscle served not only as a starting point for the study of carbohydrate metabolism in muscle, a field which attracted such notable research workers as Parnas and Meyerhof, but also, indirectly, to the development of present knowledge of alcoholic fermentation by yeast. The latter is a process which, in the main, follows precisely the same intermediate steps as does lactic acid formation in muscle. It also paved the way for studies of fermentation and kindred processes in bacteria, so brilliantly pioneered in Hopkins’ laboratory by Marjorie Stephenson.

The work on muscle emphasized the immense importance of enzymatic activity in living tissues and the extreme rapidity with which these catalysts can operate. One outcome of this was that Hopkins became interested in oxidizing enzymes, a field later developed and expanded by Malcolm Dixon, D. E. Green, and many others, again largely in Hopkins’ own department. Hopkins himself became especially fascinated by the respiratory importance of -SH compounds. He was led in this direction because, he said, “I was endeavouring to discover if vitamins were to be found among sulphur-containing compounds, and was led part of the way towards the separation of the substance now described.” This new substance was glutathione; and a series of papers on its isolation, structure, and biological function followed in rapid succession.

Some years later Hopkins was able to show that certain dehydrogenases are -SH-dependent enzymes. Although in the meantime similar conclusions has been reached by other investigators, Hopkins and his assistant, E. J. Morgan, made significant contributions to this field in 1938–1939. The knowledge accumulated on the importance of -SH groups in enzyme activity became of intense interest from 1939 on and played a very important part in connection with the possible use of vesicant gases by the enemy and in the development of British anti-lewisite.

Hopkins was much impressed by Lohmann’s discovery that glutathione acts as a specific activator for glyoxalase, a widely distributed enzyme the function of which is still unknown. Hopkins, desirous of knowing whether glutathione is or is not widely distributed, took advantage of its activating effect upon glyoxalase to carry out a massive comparative study of the distribution of the enzyme and its cofactor, thus setting the pattern for many later comparative studies.

BIBLIOGRAPHY

A partial bibliography is in Poggendortf, VI, 1158–1159. For information on Hopkins or his work, see Ernest Baldwin and J. Needham, eds., Hopkins & Biochemistry (Cambridge, 1949); and Ernest Baldwin, Gowland Hopkins (London, 1961)

Ernest Baldwin

Sir Frederick Gowland Hopkins

The English biochemist Sir Frederick Gowland Hopkins (1861-1947) was the first to recognize the necessity for "accessory factors" in the diet, thereby initiating important work in vitamin research.

On June 20, 1861, F. Gowland Hopkins was born in Eastbourne, Sussex. He attended the City of London School at Enfield (1871-1875) but was forced to withdraw because of truancy caused by "sheer boredom, " to use his own words. He then attended a private school.

Hopkins was apprenticed for 3 years to a consulting analytical chemist in London. At the age of 20 he entered the Royal School of Mines at South Kensington, where he took a course in chemistry, and after some analytical practice he studied at University College, London, for the associateship of the Institute of Chemistry. In 1883 he became assistant to Thomas Stevenson, Home Office analyst and lecturer on forensic medicine at Guy's Hospital. Meanwhile, Hopkins began to read for his degree from the University of London, and then in 1888 he began to study medicine at Guy's Hospital. In 1894 he graduated from the University of London in both science and medicine and became an assistant in the department of physiology at Guy's Hospital. In 1898 he joined the physiological department at Cambridge University as a lecturer in order to develop teaching and research in physiological chemistry. That year Hopkins married Jessie Anne Stevens; the marriage resulted in three children.

Hopkins's task at Cambridge, supplemented by tutorial work at Emmanuel College, left him little time for research. In 1910 Trinity College granted him a fellowship and appointed him praelector in physiological chemistry, a position with no formal obligations other than his own research.

During his last few years, Hopkins, who was the ablest analyst and medical specialist in England, suffered from a number of increasing disabilities, including loss of sight. His life's work had been "the exploration of the chemistry of intermediary metabolism, and the establishment of biochemistry as a separate discipline concerned with this active chemistry of the life process, and not merely with its fuels and end-products." When he died at Cambridge on May 16, 1947, he had already seen this aim accepted by scientists throughout the world. As the undisputed dean of English biochemistry, which he had established almost single-handedly, Hopkins was the recipient of many honorary degrees, honors, and prizes, including fellowship in the Royal Society (1906), knighthood (1925), the Copley Medal (1926), and the Nobel Prize in physiology or medicine (1929).

Butterfly Pigments

Hopkins's first mature research paper concerned the chemistry of the pigments of butterflies' wings. His first work on this topic appeared in 1889, but his complete research was not published until 1896 in Philosophical Transactions of the Royal Society as "Pigments of Pieridae." Hopkins showed that the opaque white substance in the wings of this butterfly was uric acid—an example of the use of a normal excretory product for purposes of ornamentation. His research on butterfly pigments led him to extend his work to uric acid problems in humans. In 1893 he published two papers describing a new method for determining uric acid in urine, which remained standard practice for many years. He published papers in 1898 and 1899 on the relation of uric acid excretion to diet, a reflection of the interest at that time in gout and its relation to uric acid formation.

Vitamin Research

Hopkins had not been long at Cambridge when he produced a piece of classic research that immediately brought him to the forefront of physiological chemists. While investigating the cause of failure of the Adamkiewicz color test (now called the glyoxylic test) for proteins, he found that the reaction was due not to acetic acid itself but to glyoxylic acid, an impurity. He then used his analytical skill to discover what substance in protein gave this purple color and consequently isolated the hypothetical amino acid tryptophan from the other amino acids present in protein digests. Rather than turning to another subject, Hopkins began feeding experiments with mice to ascertain the role of the newly discovered tryptophan in the diet. He found that although the tryptophan did not make the mice grow, it extended their life-span considerably. This experiment, one of the earliest (1907) demonstrating the importance of quality of diet, was one of the essential classic tests which brought this aspect of nutrition to the attention of the scientific world.

Hopkins's work on vitamins, summarized in his 1912 publication "The Importance of Accessory Food Factors in Normal Dietaries, " is generally regarded as his masterpiece. Although other claimants for the honor exist, there is no doubt that Hopkins was the first to realize the full significance of the experimental facts about vitamins. His work had a far-reaching effect on nutritional research all over the world.

World War I interrupted Hopkins's research activities. His next major paper, "An Autoxidisable Constituent of the Cell, " was published in 1921. An intervening lecture, "The Dynamic Side of Biochemistry, " an address he gave as president of the Physiological Section of the British Association, is noteworthy in that in it Hopkins stated his outlook on chemical processes in living tissues. He pointed out that metabolic raw material is prepared so that it will be in the form of low-molecular-weight substances, and he underscored the importance of the new idea of endoenzymes as the universal agent of the cell. He also suggested greater use of the direct method of attack to separate from tissues additional examples of the simpler products of metabolic changes, regardless of the small amounts of these that were present.

Biological Oxidations

During the 1920s the study of biological oxidations was dominated by two rival theories which were apparently incompatible: one assumed a process due to activation of pairs of hydrogen atoms by tissue enzymes called dehydrogenases; and the other assumed a process brought about by an oxygen-activating catalyst which contains iron. Both of these processes are now known to be valid, and Hopkins, to some extent, succeeded in reconciling them. He isolated a substance which he called glutathione and showed that it could exist in two interconvertible forms: a reduced form and an oxidized form. He proposed that glutathione functioned as an oxygen-carrying catalyst (called by him a coenzyme), with the disulfide oxidized form acting as the hydrogen acceptor in being reduced and then passing on the hydrogen to oxygen during its spontaneous reoxidation. This proposal seems to have furnished the first hint that intermediate hydrogen transport might occur in living tissues, a now well-established fundamental fact in the field of biological oxidation.

True Measure of Importance

The true measure of Hopkins's importance lay not only in his own research but in the inspiration he provided to numerous biochemists who spread his teachings throughout the world. The number of his students elected to university chairs in biochemistry is particularly impressive. Perspectives in Biochemistry, published in 1937 in honor of his seventy-fifth birthday by a group of Hopkins's students, gives some idea of their productivity.

At the beginning of the 20th century, physiological chemistry and biochemistry were virtually a German monopoly. In England there were literally no biochemists and only a very few physiological chemists. At the time of Hopkins's retirement, British biochemists were the equal of any in the world.

Further Reading

Much useful information on Hopkins's life is in Joseph Needham and Ernest Baldwin, eds., Hopkins and Biochemistry, 1861-1947 (1949). Detailed studies of Hopkins's life and work are the memoir by Sir Henry Dale in the Royal Society, Obituary Notices of Fellows of the Royal Society, vol. 6 (1948-1949); James Gerald Crowther, British Scientists of the Twentieth Century (1952); and Patrick Pringle, Great Discoverers in Modern Science (1955). □

Hopkins, Frederick Gowland

Frederick Gowland Hopkins (1861-1947) is credited with the discovery of vitamins and their function in the diet. Thanks to his research, we now understand the importance of these substances in promoting health and preventing disease.

Born in Sussex, England, Hopkins had a lonely and unhappy childhood. He was brought up by his widowed mother and an unmarried uncle who tended to ignore him. When Hopkins was 17, his uncle chose a career in insurance for him and for several years he dutifully gave in to his uncle's wishes. At the same time, however, he also took part-time courses in chemistry at the University of London, eventually getting his degree.

In 1888, already 27 years old, Hopkins received the small inheritance that finally enabled him to enter medical school at Guy's Hospital in London. After getting his doctoral degree in 1894, Hopkins joined the staff of Guy's Hospital and taught for several years. In 1898 he was invited to teach physiology and anatomy at Cambridge University and it was at Cambridge that his long, distinguished career really began.

In 1901, while working with S.W. Cole, a student at Cambridge, Hopkins discovered tryptophan, an important amino acid, and was able to isolate it from protein. A few years later Hopkins demonstrated that tryptophan and certain other amino acids could not be manufactured in the body from other nutrients but had to be supplied the diet. By so doing, he laid the foundation for the concept of the essential amino acids necessary for proper body functioning.

After his work with tryptophan, Hopkins's primary interest became the study of diet and its effect on metabolism (the physical and chemical processes necessary for maintaining the body). At the time, nutritional science was in a fairly primitive state. Most researchers confidently believed that a well-rounded diet consisted of the proper mixture of fats, proteins, carbohydrates, mineral salts, and water, and that the so-called diet-linked illnesses—such as beriberi or scurvy—were caused by some toxic substance in certain foods.

Studying the literature—including reports by Christiaan Eijkman (1858-1930) that polished rice seemed to cause beriberi (a nerve disease), while unpolished rice effected a cure—Hopkins began to have serious doubts about this nutritional theory.

Hopkins had already noticed that his laboratory rats failed to grow on a diet of artificial nutrients, but grew rapidly when he added tiny amounts of cow's milk to their daily rations. He suspected that normal food must contain substances missing from the pure fats, proteins and carbohydrates routinely used in nutritional studies. Hopkins called these substances "accessory food factors" and decided that they were necessary for growth. His two papers on the subject, in 1906 and 1912, are considered the first explanations of the concept of vitamins.

For their pioneering work in vitamin research, Hopkins and Eijkman received the 1929 Nobel Prize in medicine. Hopkins was knighted in 1925 and received numerous other awards in the 1920s and 1930s. He was a great inspiration to all of his students, many of whom became professors. Hopkins died in Cambridge in 1947.