Concerning the Discovery of Ascorbate

Introduction

Nitric oxide, a derivative from nitrite, reacts with an active groups in the muscle tissue comprising of (for the most part) iron and specific proteins, to create the cured meat colour.  It plays a further role as an antimicrobial agent and is partly responsible for the cured meat taste.  This make nitrite along with salt (sodium chloride) the most important curing agents.

Another key ingredient for bacon cures is ascorbate or vitamin C.  Either as sodium ascorbate or ascorbic acid or its isomer, erythorbate, either as erythorbic acid or its salt, sodium erythorbate.  The functional value of ascorbate is significant. (1)

The value of nitrite has been discovered over the last 200 years (2)  Previous articles dealt with its recognition as curing agent and how the curing industry ended up using it. (3)  We now turn our attention to ascorbate.  We first look at its discovery.

The Discovery of Vitamins

casimir
The Polish biochemist, Kazimierz Funk (1884 – 1967) or, in English, Casimir Funk.

The term “vitamin” was coined by Casimir Funk in 1912 while working at the Lister Institute of Preventive Medicine, in London.   It is a combination of the words, “vital” and “amine” meaning the “amine of life”.  In 1912, it was believed that “accessory factors” (9) in some foods, necessary for the function of the human body, prevented certain diseases like beriberi and scurvy.

It was thought that these “accessory factors” might be chemical amines.  It turned out that this is the case  with thiamine (vitamin B1), but after it was found that other such micronutrients were not amines, the word was shortened to vitamin in English.  (Wikipedia. Beriberi and Vitamin)

The discovery of vitamins happened at a time when the prevailing theory of disease was the germ theory and “dogma held that only four nutritional factors were essential namely proteins, carbohydrates, fats, and minerals.” It was however recognised in this time, by clinicians that scurvy, beriberi, rickets, pellagra, and xerophthalmia were “specific vitamin deficiencies, rather than diseases due to infections or toxins .”  (Semba RD; 2012: 1)

The period when the vitamins were discovered stretches from the early 1800’s until the mid-1900’s. (Semba RD; 2012: 1)

The discovery of the individual vitamins were not the result of big eureka moments but the fruit of the labour and contributions of many epidemiologists, physicians, physiologists, and chemists, from around the world.  Like many discoveries, “it was slow, stepwise progress that included setbacks, contradictions, refutations, and some chicanery.”  (Semba RD; 2012: 1)    This article is not an exhaustive account of the story of its discovery with every important contributor and contribution listed.  It is an overview and a general introduction to some of the main characters in the great saga.

The Discovery of Ascorbate or Vitamin C

Dr Albert Szent-Gyorgyi2
Hungarian scientist Albert von Szent-Györgyi, recipient of the 1937 Nobel Prize in physiology or medicine, “for his discoveries in connection with the biological combustion processes, with special reference to vitamin C and the catalysis of fumaric acid.”

 

Intense scientific inquiry into possible cures and preventative methods for scurvy began at the beginning of the 1800’s with the work of George Budd (1808-82), Professor of Medicine at King’s College, London. (Hughes, R. E.; 2000)

“In 1842, Budd published in the London Medical Gazette a series of articles entitled, “Disorders Resulting from Defective Nutriment.” He described “three different forms of disease which are already traced to defective nutriment” and argued that such conditions resulted from the absence of dietary factor(s) other than carbohydrate, fat, and protein, and that the absence of each of these specific factors would be associated with a specific disease.  This idea lay dormant for 40 years until it was experimentally proved by N. Lunin.  (Hughes, R. E.; 2000)

L. J. Harris who himself made significant contributions in the later history of vitamin C, referred to Budd as “the prophet Budd” and cited an article where Budd expressed the belief that scurvy was due to the “lack of an essential element which it is hardly too sanguine to state will be discovered by organic chemistry or the experiments of physiologists in a not too distant future”  (Hughes, R. E.; 2000)

Little happened, however, to fulfill Budd’s prophesy until the beginning of the twentieth century with the work of A. Holst and T. Fröhlich of Norway.  (Hughes, R. E.; 2000)

McCollum (1922) said that for growth and “prolonged well-being” in rats, the following was necessary: “A single purified protein, a source of the sugar glucose, nine mineral elements and two uncharacterized dietary factors”  (McCollum, E. V.; 1922:  365)  The two unknown dietary factors he called “A” and “B”.

It seemed natural for the scientific community to call the antiscorbutic factor they were looking for, “accessory food factor C.”  The phrase was however clumsy and people already got used to the term vitamine.  After chemists made peace with the option of dropping the e and thereby not referring to any particular chemical structure, the antiscorbutic factor was called vitamin C.

Zilva, working in the Biochemistry Department at the Lister Institute, London was leading the way and he attempted to isolate it from lemon juice.  He was able to create a solution that contained Vitamin C (the presence of which was confirmed in tests on babies) with the citric acid being removed, but as soon as it was evaporated to dryness, the functionality disappeared.   (Carpenter, J. K.; 1986:  187)

The search for Vitamin C continued with renewed vigour until the 1930’s when two different approaches both lead to the discovery of Vitamin C.  (Daniel E. P.  and Munsell H. E; 1937: 5)

The concentration of Vitamin C, derived from lemon juice was studied in depth over a long period of time.  Two German chemists, J. Tillmans and P. Hirsch (1927) observed that there is a correlation between the reducing capacity of plants and animal tissue and their Vitamin C content. (4) (Daniel E. P.  and Munsell H. E; 1937: 5)

Biological oxidation-reduction systems were also being studied where a strong reducing substance was identified with the empirical formula of CodeCogsEqn (18)  from the adrenal cortex. (5)  The substance was acidic and resembled the carbohydrates in reducing power and colour reactions.  (Daniel E. P.  and Munsell H. E; 1937:  5)

Parallel to this work was that of  Dr. Albert Szent-Györgyi’s who isolated hexuronic acid. The work of Dr Szent-Györgyi became legendary.

Dr Szent-Györgyi, “a Hungarian biochemist, was working on plant respiration systems at Groningen in Holland and became interested in a reducing compound present in his preparations.”  (Hughes, R. E.; 2000)

F. G. Hopkins, himself a valuable contributor to the work on vitamins (he demonstrated in 1912 the presence of growth factors in milk and showed their essential dietary nature) invited Szent-Györgyi to Cambridge to extend his studies. In 1927, Szent-Györgyi isolated his “Groningen reducing agent” in a crystalline, from oranges, lemons, cabbages, and adrenal glands.”  (Hughes, R. E.; 2000)

He  published his discovery in 1928, and after some struggle to find an appropriate name, called this new substance hexuronic acid.  In this paper, a statement is made about the studies on the reducing substances of lemon juice, and mentioned that they “established interesting relationships between vitamin C and the reducing properties of plant juices.”  (Daniel E. P.  and Munsell H. E; 1937:  5)

In 1930 R. B. McKinnis and C. G. King, a vitamin researcher at the University of Pittsburgh, suggested in a publication that hexuronic acid could be vitamin C.  (Halver J. E., and Scrimshaw, S.; 2006:  5, 6)  The work of King and Szent-Györgyi would find an interesting and controversial link in the person of J. L. Svirbely who previously worked with King and was appointed by Szent-Györgyi to assist him, in 1931.

While still at Cambridge, Szent-Györgyi was approached by the Hungarian minister of education, Count Kuno Klebelsberg, who wanted to rebuild the Hungarian scientific institutions with Rockefeller Foundation support for expanding the programs in Szeged.    He was invited to return to Hungary and chair the medical chemistry department at the University of Szeged. (The Albert Szent-Györgyi Papers)  With limited advancement opportunities at Cambridge, he took up the new position in January 1931.

Szent-Györgyi was an eccentric, informal, unorthodox, brilliant and very popular professor and a thorn in the flesh for many, more conservative, colleagues.  Apart from fascinating lectures, he was known for “dining or playing sports with his students, riding his bicycle to visit colleagues (as was common at Cambridge)–but the students loved him for his free and spontaneous approach to education.”  (The Albert Szent-Györgyi Papers)

Within the first six months in Szeged, he had done in terms of educational vigor and introducing educational programs and research structures, more than many people do in their lifetime.  (The Albert Szent-Györgyi Papers)

Towards the end of  1931, an American post-doctoral fellow, Joseph Svirbely, also a Hongarian native, joined Szent-Györgyi’s research team at the invitation of Szent-Györgyi.  (The Albert Szent-Györgyi Papers)  Together they conducted landmark experiments on guinea pigs, “which, like humans must ingest Vitamin C to maintain health since they also cannot produce it within their bodies.  These experiments showed that “hexuronic acid — renamed ascorbic acid to reflect its anti-scurvy properties — was indeed the long-sought vitamin C.”  (Schultz, J.; 2002)

The discovery has not been without controversy.  Who exactly discovered it first?  Was it Szent-Györgyi or another researcher who would claim this, Glen King?  Central to the controversy is  Joseph Svirbely.  This is how it unfolded.

J. L. Svirbely initially worked with C. G. King at the University of Pittsburgh, trying to isolate vitamin C, along with graduate students H. L. Sipple, O. Bessie, F. L. Smith, and W. A. Waugh.  “They were able to prepare vitamin C concentrates from lemon juice and studied the properties of vitamin C fractions from 1929 to 1931.  Otto Bessie, from Montana, did not trust J. L. Svirbely.”  It is reported that on one occasion their disagreements ended in physical blows.  (Halver J. E., and Scrimshaw, S.; 2006: 5, 6)

Svirbely completed his work in Pittsburgh under King and was awarded his Ph.D..  He received a postdoctoral fellowship to work in  Germany under Professor H. Wieland. In the fall of 1931, he changed his plans and went to Hungary when Szent-Györgyi offered him an appointment in Hungary which he was keen to take up. (Jukes, T.;  1988:  1290)

This was a strategic appointment by Szent-Györgyi.  One that was fully within his right to do and a lesson in how key appointments can swing the course of events in ones favour.

Svirbely came with all the experience he gained from working with King.    Szent-Györgyi later admitted this himself when he wrote,  “When I asked him (Svirbely) what he knew he said he could find out whether a substance contained vitamin C. I still had a gram or so of my hexuronic acid. I gave it to him to test for vitaminic activity. I told him that I expected he would find it identical with vitamin C. I always had a strong hunch that this was so but never had tested it. I was not acquainted with animal tests in this field and the whole problem was, for me, too glamorous, and vitamins were, to my mind, theoretically uninteresting. ‘Vitamin’ means that one has to eat it. What one has to eat is the first concern of the chef, not the scientist. Anyway, Swirbely [sic] tested hexuronic acid. A full test took two months, but after one month the result was evident: hexuronic acid was Vitamin C.”  (Jukes, T.;  1988:  1290)

Back in Pittsburgh, King and his colleagues were getting close to reaching a similar conclusion.  Svirbely wrote to his former mentor in March 1932, telling him about the work they have done in Szeged. He also mentioned that he and Szent-Györgyi were submitting their findings in an article to Nature.  (The Albert Szent-Györgyi Papers) (8)  From this, it may seem that this prompted King to a hasty submission of what was still to him inconclusive results.  There are evidence that this is not the case and the inference will be wrong. That the conclusions of King, based on work with lemon juice, was completed well before he received the letter from Svirbely.  That he may have hastily submitted work for publication that was “sitting” with him after receiving word from Svirbely, is a matter that should have no bearing on the priority of the discovery.  (Jukes, T.;  1988:  1292)

The following month, on 1 April 1932, Science published King’s paper where he announces that he discovered vitamin C, and that it is identical to hexuronic acid. “King cited Szent-Györgyi’s earlier work on hexuronic acid where he gave Szent-Györgyi full credit for isolating it.  (Jukes, T.;  1988:  1292)

He did however not credit him for vitamin C, despite the note he received from Svirbely, claiming this.  As much as the appointment of  Svirbely by Szent-Györgyi was a prudent decision, fully within his rights, so was it fully within King’s right not to mentioned the unpublished report on the findings of Szent-Györgyi of a link between vitamin C and hexuronic acid.

Glen King
C. Glen King. 1954.

The discovery by King was picked up quickly by the American press.  (The Albert Szent-Györgyi Papers) This initial report “was followed by a more lengthy and descriptive report in the Journal of Biological Chemistry by Waugh and King in 1932.”  (Halver J. E., and Scrimshaw, S.; 2006:  5, 6)

King remembers the sequence of event and the order of the communication from Svirbely as follows, “We then submitted our paper for the spring meeting of the American Society of Biological Chemists … and sent another manuscript to Science. A few weeks later in March, I received a letter from Dr. Svirbely (who had gone to Hungary to study with Szent-Györgyi the fall of 1931), in which he mentioned that they were just finishing their first assay in which animals grew satisfactorily and were protected from scurvy when given 1 mg/day of their crystalline ‘hexuronic acid’. They were sending a report of the assay to Nature.” (Jukes, T.;  1988:  1290, 1291)

The researchers in Szeged did not see things King’s way.  In reality, King did received the note from Svirbely before the publication in Science,  (Jukes, T.;  1988:  1290, 1291)   They were shocked by what they saw as an the early announcement, prompted by the note.  They felt that their findings had priority.  “Astonished and dismayed, Szent-Györgyi and Svirbely sent off their own report to Nature, challenging King’s priority in the discovery”  (The Albert Szent-Györgyi Papers)

Science did not record the date when thy received the submission from King.  Today we only have the publication date.  It is of course entirely possible that they received it well in advance before King received his note from Svirbely and the actual publication was delayed for an unknown reason.  King may himself had reasons why he submitted it late.  There are reports that he was in the process of checking certain facts and other work that was published that would have a bearing on his work if they were correct.  (Jukes, T.;  1988:  1290, 1291)

The fact that the note and timing of the publications became such a controversy is understandable.  Both worked hard over many years on identifying vitamin C and each felt that they had a claim to its first identification.  They worked independently and, at the same time relied on each others work.  In the case of Szent-Györgyi, through his identification of hexuronic acid and in King’s case, in the establishment of the techniques for analysis that was transferred by Svirbely.  The consternation that followed in both camps after the publication of King’s work and when Szent-Györgyi was credited with the discovery and isolating vitamin C was to be expected.  Such is life.  It makes for, as Jukes puts it, one of the strangest accounts of the discovery of a vitamin.

Further work by Svirbely and Szent-Györgyi (1932) confirmed that Hexuronic Acid was vitamin C. (6)  (Daniel E. P.  and Munsell H. E; 1937: 5) “The fact that King had worked on the problem for over five years was well-known in the scientific community.  Especially in the United States and he had “many supporters, who were ready to vilify Szent-Györgyi as a plagiarist.”  However, Europeans and British scientists also knew about the work of Szent-Györgyi’s and his “long history with this anti-oxidant substance”.  They accepted his claim of being the first to discover vitamin C.  (The Albert Szent-Györgyi Papers)

Albert Szent-Gyorgyi and his laboratory staff at Szeged.jpg
Albert Szent-Gyorgyi and his laboratory staff at Szeged, Hungary

The emphasis now shifted to understand the structure of vitamin C.  A tentative formula for vitamin C was suggested by Hirst et al (1932) and Herbert et al (1933). (7)  (Daniel E. P.  and Munsell H. E; 1937:  5)   Even though Szent-Györgyi’s credit for the first identification of vitamin C was a bitter and lifelong disappointment to King, together with his research team, they published over 50 papers on ascorbic acid’s characteristics, deficiencies, and enzyme activities in various animal tissues between 1932-1942   (Halver J. E., and Scrimshaw, S.; 2006:  5, 6)

Haworth, a Birmingham (U.K.) chemist, received from Szent-Györgyi a sample of his “hexuronic acid, and in 1933, “in a series of impressive papers, the Birmingham chemist, using both degradative and synthetic procedures, described the structure of the molecule (Hughes 1983). The molecule was synthesized simultaneously, but independently, by T. Reichstein in Switzerland and by Haworth and his colleagues in Birmingham, both groups using essentially the same method.”  (Hughes, R. E.; 2000)

The work of King and his research team came to fruition when Burns and King reported the synthesis of 1-C14-L-ascorbic acid in Science in 1950.”  (Halver J. E., and Scrimshaw, S.; 2006:  5, 6)

Over the years, the story of the analysis by Szent-Györgyi and Svirbely would become part of Chemical history’s folklore.

Conclusion

The history of the discovery of ascorbate becomes an important introduction into our future consideration if its mechanism and functionality.  It introduces us to biological combustion processes and ascorbate’s value as reducing agents.

It takes this vitamin out of the realm of academia and makes it “accessible” by giving it a human face in the persons of King and Szent-Györgyi.   Szent-Györgyi tells a story involving his wife and supper that gave him the inspiration to examine paprika for a possible source of vitamin C.

In 1933, he was looking for additional, natural sources of ascorbic acid to use in further study’s.  Orange and lemon juice have high levels of ascorbic acid, but they also contain sugars that complicated purification. “Szent-Györgyi solved the problem by making imaginative use of the local specialty, paprika.”  (Schultz, J.; 2002)

“Szeged is the paprika capital of the world.”  Szent-Györgyi accounts how his wife prepared supper one night with fresh red paprika.  He writes, “I did not feel like eating it so I thought of a way out. Suddenly it occurred to me that this is the one plant I had never tested. I took it to the laboratory … [and by] about midnight I knew that it was a treasure chest full of vitamin C.”  (Schultz, J.; 2002)

Within weeks he was able to extract almost 1.4L of pure crystalline ascorbic acid from paprika, “enough to show — when fed to the vitamin C-deficient guinea pigs — that the acid was equivalent to vitamin C.”  (Schultz, J.; 2002)

The story of the discovery of ascorbate is a human story.  Rivalry, controversy and disappointment but also of triumph, tenacity, discovery and the creative mind.  To us in the meat curing industry, ascorbate would become the reducing agent of choice in our brine preparations and the story of its discovery, an example of a life of passion, excellence and another contribution by the favourite spice of Roy Oliver (the production manager for Woodys Consumer Brands) –  paprika!

 

Notes

1.The Function of Ascorbate in Bacon Curing

There are at least four benefits in using ascorbate in meat curing.
a.  Ascorbate or its isomer, erythorbate were originally used to speed up cured meat colour formation.  (Pearson, A. M. and Tauber, F. W.;  1984:  53)  It achieves this apparently by reducing the brown meat pigment, metmyoglobin to myoglobin with its purple-red colour.  (Chichester, C. O.; 1984:  14)
b.  “Ascorbate reacts chemically with nitrite to increase the yield of nitric oxide from nitrous acid.  Nitric Oxide is responsible for meat curing.”  (Pearson, A. M. and Tauber, F. W.;  1984:  53)
c.  “Excess ascorbate acts as an antioxidant, thereby stabilising both colour and flavour.  It prevents rancidity and the fading of sliced bacon when exposed to light.  It achieves this through the prevention of heme-catalyzed lipid oxidation which results in both pigment degradation and rancidity.  As long as excess ascorbate is present, the pigments are protected against breakdown.     (Pearson, A. M. and Tauber, F. W.;  1984:  53)
d.  Under certain conditions, ascorbate has been shown to reduce nitrosamine formation.  (Pearson, A. M. and Tauber, F. W.;  1984:  53)

Only sodium ascorbate or sodium erythorbate (as opposed to ascorbic acid and erythrobic acid) are used in meat cures since ascorbic and erythorbic acid reacts with nitrite to form nitrous oxide.  Nitrous Oxide is dangerous in confined spaces and its formation reduces the amount of nitrite available to participate in meat curing.  (Pearson, A. M. and Tauber, F. W.;  1984:  53)

2.  The Function of Nitrite and Nitric Oxide in Bacon Curing
Nitrite is the starting ingredient in meat curing.  It undergoes several reactions in  the meat, ending with the formation of Nitric Oxide.  Nitric Oxide is the active ingredient that combines with meat pigments.

3.  Articles I have written on the subject of nitrite in curing brines.

Formal Article’s:

Concerning the direct addition of nitrite to curing brine

Concerning Nitrate and Nitrite’s antimicrobial efficacy – chronology of scientific inquiry

Concerning Ladislav NACHMÜLLNER and the invention of the blend that became known as Prague Salt

Factual, but an informal story format:

The history of curing

4.   Tillmans, J. and Hirsch, P.  Über das Vitamin C.  Biochem Ztschr 250:  [312] – 320; Zilva, S. S. 1927.  The Antiscorbutic Fraction of Lemon Juice.  v. Biochem.  Jour. 21:  689 – 697; 1928.  Jour 22:  779 -785

5.  Szent-Györgyi, A.  1928.  Observations on the Function of Peroxidase Systems and the Chemistry of the Adrenal Cortex. Biochem. Jour. 22:  1387 – 1409.  illus.

6.  Svirbely, J. L. and Szent-Györgyi.  1932.  The Chemical Nature of Vitamin C.  Biochem.  Jou. 26:  865 – 870.illus. and by the same authors, Hexuronic Acid and the Antiscorbutic Factor.  Nature [London] 129:  576

7.  Herbert, R. W., Hirst, E. L., Percival, E. G. V., Reynolds, R. J. W. and Smith, F.  1933.  Constitution of Ascorbic Acid.  Jour. Chem. Soc. [London] 1933 (pt. 2):  1270 – 1290. and Hirst, E. L.  1932.  Hexuronic Acid as the Antiscorbutic Factor.  Nature [London] 129:  576 577

8.  King, C. G.  and Waugh, W. A.  1932.  The Chemical Nature of Vitamin C.  Science (n.s.) 75:  357 – 358 and  Waugh, W. A. and King, C. G.  1932.  Isolation and identification of Vitamin C.  Jour. Biol.  Chem.  97:  325 – 331.  illus.  (Wikipedia.  Beriberi)

9.  The first person to postulate that certain foods contained “accessory factors” (in addition to in addition to proteins, carbohydrates, fats, and salt), necessary for human life was Sir Frederick Hopkins in 1898.

 

References

The Albert Szent-Gyorgyi Papers.  Szeged, 1931-1947: Vitamin C, Muscles, and WWII.  U.S. National Library of Medicine

Carpenter, J. K..  1986.  The History of Scurvy and Vitamin C.  Cambridge University Press.

Chichester, C. O..  1984.  Advances in Food Research, Volume 29.  Academic Press, Inc.

Daniel E. P.  and Munsell H. E.  1937.  Vitamin Content in Foods.  United States Department of Agriculture.

Halver J. E., and Scrimshaw, S..  2006.  CHARLES GLEN KING 1896–1988.  A Biographical Memoir.  Biographical Memoirs, VOLUME 88.  National Academy of Sciences.

Hughes, R. E..  2000. Vitamin C.  Cambridge World History of Food.  2000.  Editor: Kenneth F Kiple & Kriemhild Conee Ornelas. Volume 1. Cambridge, UK: Cambridge University Press.

Jukes, T..  1988.  The Identification of Vitamin C, an Historical Summary.  University of California, Berkeley, CA 94720, from  American Institute of Nutrition. Received 29 lune 1988. /. ÑutÃ-.118: 1290-1293, 1988

McCollum, E. V., The newer knowledge of nutrition, New York, 2nd edition, 1922.

Pearson, A. M. and Tauber, F. W..  1984.  Processed Meats, second edition.  AVI Publishing Company, Inc.

Pereira, C., Ferreira, N. R.,  Rocha, B. S.,  Barbosa, R. M., Laranjinha, J..  2013.  The redox interplay between nitrite and nitric oxide: From the gut to the brain.  Redox Biol. 2013; 1(1): 276–284. Published online 2013 May 9. doi: 10.1016/j.redox.2013.04.004

Ridd, J. H..  1998.  Some Unconventional Pathways in Aromatic Nitration, Acta Chemica Scandinavica, 1998:  52:  11 – 22

Semba RD.  2012.  The discovery of the vitamins.  Int J Vitam Nutr Res. 2012 Oct;82(5):310-5. doi: 10.1024/0300-9831/a000124.

Schultz, J..  2002.  Albert Szent-Györgyi’s Discovery of Vitamin C,  International Historic Chemical Landmark.  On occasion where the American Chemical Society and the Hungarian Chemical Society designated Albert Szent-Györgyi’s work in biological combustion and the identifying of vitamin C as an International Historic Chemical Landmark with a ceremony at at the University of Szeged Albert Szent-Györgyi Medical Faculty in Szeged, Hungary.

https://en.wikipedia.org/wiki/Beriberi

https://en.wikipedia.org/wiki/Vitamin

 

Images

Picture 1:  Casimir Funk.  http://beforeitsnews.com/health/2014/08/synthetic-vitamins-are-toxic-2545050.html

Picture 2:  Albert von Szent-Györgyi.  http://www.chemistryexplained.com/St-Te/Szent-Gy-rgyi-Albert.html

Picture 3:  C. Glen King.  1954.  http://www.asbmb.org/uploadedfiles/aboutus/asbmb_history/past_presidents/1950s/1954King.html

Picture4:  Albert Szent-Gyorgyi and his laboratory staff at Szeged, Hungary:  https://profiles.nlm.nih.gov/ps/retrieve/Narrative/WG/p-nid/149/p-visuals/true

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