James L. Franklin
Chicago, Illinois, United States

On December 10, 1986, Rita Levi-Montalcini and Stanley Cohen shared the Nobel Prize in Physiology or Medicine for their work in neurobiology and for the discovery of “nerve growth factor” (NGF) that has since shed light on tumors, wound healing, and other medical problems. Levi-Montalcini was the first Italian recipient of the prize in sixty years and the fourth woman in the category of physiology or medicine.¹ Her life and the journey that led to Stockholm is inspiring and one that deserves a granular telling. It is a chronicle of how she obtained an education in science and medicine in spite of immense social pressures; how as a Jew in fascist Italy, her very survival in peril, she managed to continue her research amidst the chaos of World War II; and how, after enduring the dislocation of war, she was able to resume her academic career and research in neuroembryology. The path that led to her discovery of NGF is illustrative of the maxim “chance favors the prepared mind.” Chance, however, was coupled with two traits she believed essential to success and personal fulfillment in a scientific career: “total dedication and a tendency to underestimate difficulties which cause one to tackle problems that other more critical and acute persons instead opt to avoid.”²

Rita Levi-Montalcini (let us refer to her as Rita) was born in Turin, the industrial and cultural center of northern Italy in 1909. It was the capital of the Piedmont region set along the banks of Italy’s longest river, the Po. With the unification of Italy (the Risorgimento) in 1860, Turin became Italy’s first capital under King Victor Emmanuel II of Savoy. Rita and her fraternal twin sister Paola were the children of Adele Montalcini, a talented artist, and Adamo Levi, an electrical engineer and mathematician.³ The twins had two older siblings: her brother Gino, who was seven years older, and her sister Anna (Nina, the family nickname), who was five years her senior. They were an upper-class Jewish family and lived comfortably in a fourth-floor apartment overlooking the large avenue of Corso Umberto, which lead to a nearby square featuring an imposing monument to Vittorio Emmanuele II. Rita enjoyed a loving and privileged childhood with a maid, governess, and chauffeur. The family was able to spend the hot summer months in a vacation house in the Asti Hills. The total population of Turin in 1911 was 430,000, while the Jewish population of Turin and the surrounding areas was about 6,700.

Her mother’s family, who had traced their origins as far back as the fourteenth century, had originally settled in the Tuscan city of Montalcino at the time of the Republic of Siena (the 12^th to 16^th century). Her father Adamo’s family were Sephardic Jews who were well integrated into Italian society and had many Catholic friends. Although her family was nominally Jewish, they rarely attended synagogue except on Yom Kippur. On Passover, they would attend a family seder at the home of more observant relatives. Rita was perplexed as to how to respond to playmates from the neighborhood, most of whom were Catholic, who wanted to know her religion. Her father counseled her to tell them that they were “free thinkers.” He told her that when she was 21, she could decide what religion she wanted to adopt.

Despite the family’s lack of practice, in terms of religion, her father held strong beliefs—and this was not the only subject. He determined that his daughters would attend a nearby high school for girls, which offered no possibility of attending a university, as mathematics and the exact sciences were not included in the curriculum. His conviction stemmed from observing two of his sisters who had earned doctorate degrees in literature and mathematics, which was very unusual at the time, and who both struggled to continue their careers while handling marital and maternal obligations. Rita saw how in the case of her older sister, Anna, those roles subsumed aspirations to become a writer, as she was soon married after her schooling was complete and began a family. For her twin sister Paola, their father’s decision did not create a serious dilemma. Paola had gotten excellent grades and pursued a career in art, a talent she had exhibited early in childhood. For Rita, though, the decision was problematic. She had shared with her older sister a passion for literature, desiring to write. On completing high school, she realized she had no desire for marriage or motherhood and found herself adrift. It was at this time she witnessed the suffering and death of a beloved governess from stomach cancer. The experience kindled a wish to study medicine. But she faced two hurdles: first, convincing her father to support this plan; and second, because she lacked the science background required for admission to medical school, she would have to receive private tutoring to pass the required examinations.

Finally, at the age of 20, she was able to convince her father “not to stand in her way” and allow her to pursue a medical career. In preparing for the exams as an “external candidate” (home study), she recruited a cousin, Eugenia de Lustig, whose educational background was similar to her own, to embark on an eight-month course of study of Greek and Latin with Professor Lobetti-Bodoni and mathematics with Professor Guido Ascoli, both highly regarded teachers in Turin. Recollecting in her memoir In Praise of Imperfection, “It was in the autumn of 1930 that I entered for the first time the somber and stately amphitheater of the Institute of Anatomy of the Turin School of Medicine.” Freshmen and sophomores together attended a two-year course in normal human anatomy. Of some 300 students, she and her cousin Eugenia were two of seven “girls” split between the freshman and sophomore class who endured “the less gallant remarks about their aesthetic merits.” It was during her gross anatomy lectures that she was first introduced to Professor Giuseppe Levi, who was universally feared and respected by her classmates. Legendary for his fearful rages, a booming voice, and red hair, his research was in the histology of the nervous system. In spite of his imperious manner, Levi would become a surrogate father who nurtured her endeavors in research until his death in 1965. Giuseppe Levi had the distinction of mentoring three Nobel Prize recipients: Rita, Salvador Luria, and Renato Dulbecco. All three became close friends in Turin and, enduring similar hardships, would remain such throughout their careers.

In 1936, Rita graduated summa cum laude from the Turin School of Medicine and remained at the university as Levi’s research assistant. It was in his laboratory that she would master the techniques of histology and the chrome-silver impregnation stain, which makes nerve cells stand out in the smallest detail. The stain had been discovered by Camillo Golgi and pioneered by the Spaniard Santiago Ramón y Cajal in the study of the nervous system, for which both men shared the Nobel Prize in Physiology and Medicine in 1906. Cajal succeeded in identifying the different cell populations of the nervous system by analyzing the earliest stages of development in the chick embryo. By 1938, Rita was collaborating with Fabio Visentini, an electrophysiologist, in studying the motor and sensory centers of chick embryos. Unfortunately, this research came to a dramatic end in September 1938 when Mussolini instituted racial laws that in part forbade Jewish students and faculty members, including her mentor Levi, from access to university premises. Rita was allowed to complete a specialization course she had begun in neurology and psychiatry at the Clinic for Nervous and Mental Diseases but was obliged to discuss her dissertation in a separate session for Jewish students. Her research with Visentini was rejected when it was submitted to an Italian specialty journal “because it was excessively tainted with Judaism”; they were forced to publish the results in a Swiss journal.

By March 1939, no longer able to work at the university, she accepted an invitation to continue her scientific work with Dr. Léon Laruelle, director of a neurological institute in Brussels. Her decision was influenced in part because Giuseppe Levi was nearby in Liége at the Institute of Pathologic Anatomy, and also because her family had fled the mounting danger in Turin to Westende on the Flemish coast. Belgium was gripped by the fear of imminent conflict, felt most acutely by older citizens who had suffered the consequences of German invasions in the Great War. For these reasons, Rita did not return to Turin until Christmas Day. During her months in Belgium, according to historian Marco Piccolino, her aspiration to pursue experimental research became well defined.⁴

Back in Turin and still unable to attend the university, Rita attempted to practice outpatient medicine in a “clandestine fashion.” She tried to look after patients who had been under her care at the university’s clinic but was constrained by having to turn to Aryan doctors to sign her prescriptions, thereby placing them in danger as well. Ultimately, she was forced to abandon this activity. By the spring of 1940, Germany had rapidly occupied Denmark, Norway, the Netherlands, Belgium, and France, leading Mussolini to declare war on France and Great Britain. Inactivity weighed heavily on Rita, and she found herself depressed, restless, and unmotivated. In a surprise visit, Rodolfo Amprino, a colleague from her days in the Anatomy Institute who she had not seen for eight years, brusquely challenged her to take up her interrupted research. He held up the example of Ramón y Cajal, who in a poorly equipped lab in Valencia had revealed foundational knowledge of the nervous system.

Thus began a new chapter in her career: the equipping of a laboratory in her family’s apartment, which they still occupied after the death of her father in 1932⁵; she referred to this bedroom lab as “á la Robinson Crusoe.” Assembling a laboratory dedicated to her delicate work posed significant challenges, the foremost being the purchase of two Zeiss microscopes, one with low magnification for microdissection and the other with high magnification for cellular detail. Before embarking on this project, as described in her memoir, a family conference was convened, and she secured the approval of her mother, brother, and twin. Her brother Gino, an architect, built her a sterile “thermoregulated box” with openings for embryo operation. Her lab also required assembling improvised surgical equipment and reagents for preparing histologic materials. The “tour de force” was fitting everything into her small room. Fortunately, the family had the resources to purchase the array of equipment. Increasing air raids frequently forced them into bomb shelters, into which Rita would carry her treasured microscopes.⁶

During this period, she recalled, her “aim was to analyze how excision of still non-innervated tissues in the peripheral territories, or limbs, affects the differentiation and subsequent development both of motor cells in the spinal cord and sensory cells in the dorsal root ganglia.” The inspiration for this project came to her one summer day while riding to a small mountain village in an open cattle car with her friend Guido. With her legs dangling over the side of the car, she read an article by Viktor Hamburger,⁷ given to her by Levi from an American journal. Hamburger was a pupil of the German biologist and Nobel Prize winner Hans Spemann, and he had studied how ablation of the chick embryo limb buds affected the sensory and motor neurons responsible for their innervation. Using the chick embryo model, he had observed “that one week after the operation, the motor column and the sensory spinal ganglia were greatly reduced in volume.” Hamburger interpreted these findings as pointing to the absence of an inducing factor normally released by the extirpated tissues necessary for the differentiation of motor and sensory nerve cells. As Rita notes in her memoir:

I don’t know how far the idyllic circumstances in which I read the article contributed to my desire to delve into this phenomenon, but in memory my decision is indissolubly bound with that summer afternoon and the smell of hay wafting into the wagon. I did not imagine at the time however, that this intent and my subsequent research would determine my future.

During the winter and spring of 1942, her experiments proceeded well. Professor Levi, who had also returned to Turin from Belgium, joined her in her laboratory, now more as her assistant—albeit a somewhat dangerously heavy-handed one. Studying serially the development of neural tissues to the twentieth day of incubation, they found that neurons developed normally until they reached the stump of the amputated limb, then underwent a degenerative process. Rather than the absence of an inductive process originating in the amputated limb as suggested by Hamburger, they interpreted the cellular death as the absence of a trophic effect. Here one begins to see the first hint of the thinking that would lead to the discovery of nerve growth factor.

By the latter half of 1942, the Allied bombing of Turin and industrial cities of Northern Italy had become so dangerous that Rita and her family, as well as her lab, retreated to a small house in the highlands of Astigiano, 55 kilometers east of Turin. There she worked at a small table in the family dining area. Eggs were scarce, and she had to ride her bicycle to neighboring farms and beg for fertilized eggs to continue her experiments until the war again intervened. On July 25, 1943, Mussolini was forced to resign, and in his place, King Victor Emmanuel III appointed Pietro Badoglio to head the new government. The event was met with jubilation by Italians, who were generally oblivious to the German troops massing on their frontier; the small Jewish community knew they were in the “Nazi gunsights.” By September, German troops and tanks occupied Turin. Rita’s family had no option but to flee. Furnished with fake identity cards and false surnames by partisans, they boarded a train heading south to Florence. Through a friend of her sister Gina, they were taken in by a Signora Consilia Leoncini, who agreed to rent a room on the condition they were not Jews. They remained with the Leoncini family until May 1945.

In September 1943, Italy had been divided into two regimes. German troops “liberated” the northern cities, freeing Mussolini, who had been under arrest, and proclaiming him head of the Italian Social Republic (RSI), a puppet state based in the town of Salò on Lake Garda. The policies of the new government were fiercely anti-Semitic, resulting in the confiscation of Jewish property, internment within Italy, and deportation to concentration camps including Dachau and Auschwitz. Of over 8,000 Jews deported between 1943 and 1945, only 610 survived.

What had been a very dangerous situation for Rita and her family ended in August 1944. Initially, with the exception of the Ponte Vecchio, all bridges across the Arno had been destroyed, leaving the city without electricity, food, and water. But on August 11, the entire city rose up against the Germans. By September 2, partisans and Allied troops liberated Florence. Rita, donning a Red Cross insignia, devoted herself to caring for war refugees under primitive and extreme conditions. Overcrowding led to an epidemic of typhus. The emotional toll of impotence in the face of suffering and death further convinced her that she was not cut out to practice medicine.

By April 1945, the Allies had freed the Po Valley and the entire northern region from Piedmont to Veneto. On April 28, Mussolini, disguised as a German officer, attempted to escape Italy, but was killed by partisans and hung upside down in Piazzale Loreto, Milan, his body and that of his mistress “displayed for the vituperation of those who had once been happy to cheer him.” By May, because of her medical service, Rita was allowed to travel with her brother north by military truck first to Milan and finally to Turin.

The end of the war brought an end to the racial laws in Italy. Professor Levi was returned to his position as professor at the University of Turin, and he offered Rita her previous position as assistant. Possessed of inexhaustible energy, Levi resumed the activity “he had been engaged in for more than half a century,” but for Rita, the scars were inward. She felt the inadequacy of her training and enrolled in a course of biological study to rectify the deficit. Her doubts as to the direction of her research were resolved in the summer of 1946 when Levi showed her a letter he had received from Viktor Hamburger, then chairman of the department of zoology at Washington University in St. Louis. The results of the studies she and Levi had performed “à la Robinson Crusoe” had appeared in the Belgian Archives de Biologie in 1942. Hamburger, having read these papers, asked Levi if she might be allowed to spend a semester in St. Louis to further investigate the issues raised (i.e., the cause of the loss of neural elements in response to limb extirpation). Not wishing to interrupt her course of study and experiments already in progress, she delayed her departure until September 1947.

She sailed from Genoa aboard a Polish ship, the Sobieski, accompanied by friend Renato Dulbecco, who headed to the University of Indiana to work with Salvador Luria. Disembarking in New York, Rita spent two days touring the city with a cousin who lived in New Jersey. She then traveled by train to St. Louis and Washington University, where she was warmly welcomed by Hamburger. He had seen to it that she had suitable living arrangements and welcomed her to his home for dinner her first evening in the city. So began this new phase in her career—what was to have been a few months of research morphed into thirty years as a faculty member of the zoology department at Washington University.

Viktor Hamburger—“Victor,” as he was known to friends and colleagues—was born in the small Silesian town of Landeshut on July 9, 1900. His interest in developmental biology was kindled by a two-summer advanced course in experimental biology in Heidelberg, which led him to the University of Freiburg and the laboratory of Hans Spemann. A life-changing event occurred in 1932 when he was awarded a Rockefeller Fellowship to work at the University of Chicago, where Frank R. Lillie’s laboratory excelled in experimental studies of the chick embryo. While at the University of Chicago in April 1933, Viktor received a letter from the dean of faculty at Freiburg informing him that under the recent law “for the cleansing of the professions,” he had been dismissed from his faculty position with the zoology department. The Rockefeller Foundation responded quickly by creating emergency funds to support displaced German scholars. By the fall of 1935, he had been offered an assistant professorship at Washington University, becoming chairman of zoology in 1941.⁸ That he and Rita would establish a close bond is evident in their shared love of research and struggle with anti-Semitism in their native countries. Rita brought to the study of neurobiology at Washington University her excellence as a neuroanatomist, her mastery of silver-impregnation methods for studying neural tissue, and her grasp of the field of neuroembryology. Their initial efforts centered around reexamining the effect of limb ablation on the developing nervous system.

The crucial moment on the path to the discovery of NGF came on a freezing, snowy morning in January 1950. Viktor shared a letter he had received from a former student, Elmer Bueker, describing experiments he had performed implanting bits of mouse sarcoma on the vesiculated membrane that envelopes a chick embryo. He observed a rapid proliferation of nerve fibers from nearby sensory ganglia after eight days of incubation. Both Rita and Viktor believed that they should interrupt their current work and repeat these experiments to investigate the phenomenon further. Bueker was informed and “flattered” by their interest in his work. Using two strains of mouse sarcoma, S-37 and S-180, Rita observed nerve fibers growing profusely from the embryo and invading the tumor “like rivulets flowing over a bed of stones.” It was an epiphany for Rita, evoking the Piedmontese expression “smelling the fragrance of truffles in the air.” Perhaps Bueker undervalued what he found or was distracted by other projects, but Rita immediately knew the finding was pointing the way forward. The goddess of chance (La Fortuna) was shining her light on a prepared mind.

The findings pointed to a “humoral” substance produced by the tumors that stimulated neural cellular growth, but there was much work to be done to understand it. In September 1952, Rita, concealing two white mice with transplanted sarcoma in her coat, traveled to Rio de Janeiro to work with Hertha Meyer in the laboratory of Carlos Chagas, director of the Institute of Biophysics of the University of Rio de Janeiro. Before the war, and until the anti-Semitic campaigns began, Meyer worked for six years with Professor Levi in Turin, maintaining tissue culture facilities for studying axonal growth. She left Italy to work with Carlos Chagas in setting up a specialized unit for in vitroculture techniques. At first the in vitroexperiments proved very difficult, but finally Rita was able to place small fragments of sarcoma within one to two millimeters of explanted chick embryo sensory ganglia. She observed a “striking outgrowth of neuronal processes giving the ganglia a characteristic halo-like appearance,” and this “halo” produced by the tumor had the potential to serve as a bioassay. While in Rio until January 1953, Rita kept Viktor informed of her work by including careful pen-and-ink drawings of the “halo” effect in her letters.⁹

While Rita was in Rio, Viktor had realized that further progress in understanding the tumor effect on nerve growth would require a biochemist. He offered Stanley Cohen, who was completing a postdoctoral fellowship at Washington University in physical chemistry, a research position. Cohen, the son of Jewish immigrants, was born in Brooklyn in 1922 and had earned a doctorate from the University of Michigan. At the time, Cohen was thirty and married with two children, a modest man arriving at work each morning with his dog Smog and a pipe in his mouth. “Stan” and Rita, from the winter day in 1953 when they first met until 1959, conferred frequently on “the sequence of events, each turn of which revealed the properties of that mysterious character who having made an appearance in Rio, [and] received identification papers in 1954, to become known as Nerve Growth Factor.”¹⁰

For Rita, these were the most productive six and a half years of her life. The “fibrillar halo” phenomena proved the basis of a bioassay for NGF. It was first identified as a nucleoprotein. On the advice of another future Nobel Prize winner, Arthur Kornberg, Stan treated the sample with snake venom, which split off the nucleoprotein, proving that the protein part of the molecule was the active component. Further study revealed that snake venom and male mouse salivary glands were rich sources of NGF, while antivenom inactivated it. In addition to his work with NGF, Cohen also discovered and purified the epidermal growth factor (EGF) molecule, which bears a powerful proliferative effect on connective tissue and dermal tissue.

In December 1958, Viktor informed them that budgetary restriction prevented him from offering Stan a permanent position at Washington University, forcing Cohen to accept a position at Vanderbilt University School of Medicine. Rita wistfully watched him depart “one hot July evening … his limping step [from childhood polio], smoking his pipe, Smog as always by his side.” She would often ask herself:

[W]hat lucky star caused our paths to cross. … If I, in fact knew nothing about biochemistry, Stan when he joined us had but vague notions about the nervous system. … Rita, Stan said one day, you and I are good, but together we are wonderful.¹¹

With Cohen’s departure from Washington University, Rita began to feel the emotional tug of her family and homeland. A solution was found through her collaboration with a young scientist at Washington University, Pietro Angeletti. Facilitated by Viktor through the dean’s office, she received a grant to establish a laboratory in Rome with ties to Washington University and continue her research on NGF. Eventually she would alternate at six-month intervals with Angeletti between Rome and St. Louis. Her activities in Rome continued to expand, and with additional funding, she was invited to direct the Research Center for Neurobiology in Rome, attracting promising young scientists whom she could mentor and instill her love for research within.

In 1959 when Rita and Stan first announced their discovery of NGF, it initially attracted little enthusiasm, but over the subsequent two decades, NGF studies soared in many well-organized laboratories. By 1971, two researchers at Washington University had worked out the molecular structure of the protein. It was shown to be critical for the survival and maintenance of sympathetic and sensory neurons and of pancreatic beta cells, which produce insulin, as well as playing a role in the regulation of the immune system.

Rita retired from Washington University in 1977. During the years leading up to October 1986 when she and Cohen were awarded the Nobel Prize for Physiology or Medicine, she garnered an impressive series of awards and honorary degrees. Viktor, who had continued to work at Washington University until his retirement in 1980, was not included in the Nobel Prize. This omission resulted, sadly, in a severing of the strong bond of friendship between them. The misunderstanding was fueled by inaccurate reporting of some remarks she had made on the issue and allegations that an Italian pharmaceutical company had pressured the Nobel committee to give her the prize. Ultimately, the Swedish newspaper Dagens Nyheter was forced to retract its accusation, but the damage was done and caused a scar that never healed.¹² A review by W. Maxwell Cowan in the Annual Review of Neurosciences attempted to right the wrong by highlighting the crucial role Hamburger played in the discovery.¹³ Rita donated her share of the Nobel Prize to various charities and to the restoration of Jewish monuments in Italy.

Rita’s shared childhood dream to be a writer had been put on hold upon witnessing her sister’s engagement, marriage, and motherhood. A love of literature persisted, and Rita’s reading ranged from Ludovico Ariosto to William Butler Yeats and Primo Levi. She rekindled her ambition in 1987 by writing her memoir Elagio dell’imperezione, which was translated into English as In Praise of Imperfection (1988). The writing displays a literary flare with allusions to the poetry of Yeats and moving accounts of her family, the rise of fascism in Italy, her education and career, and the friendships she formed with colleagues both in Italy and in her adopted home in the US at Washington University. She went on to write ten books in Italian that included Eva era Africana (Eve Was African) on women in Africa, La galassia mente (The Galaxy of the Mind) exploring the origins of the science of the mind and nervous system, and L’altra parte del mondo (The Other Part of the World) analyzing global objectives for the third millennium that included eradicating poverty, illiteracy, and universal education. In 2001, at the age of ninety-two, she was appointed life senator to the Italian Parliament by Carlo Azeglio Ciampi, president of the Italian Republic. It was a title only given to one other woman in the history of the Italian Republic and a duty she fulfilled to the age of 103. As a public speaker and through her writing, she championed an enlightened attitude toward aging, stressing continued engagement and learning.¹⁴

Rita Levi-Montalcini was a scientist, an innovator, and a humanist. She challenged familial expectations. She was fortunate to have two mentors to shape and foster her career, Giuseppe Levi and Viktor Hamburger. Years studying neuroembryology allowed her to grasp the meaning of the neurotropic effect induced by mouse sarcoma tissue first observed by Elmer Bueker, pointing the way to the discovery of NGF. Returning to Italy after winding down her career at Washington University, she dedicated herself to supporting and creating an innovative laboratory that would enhance the nation’s standing in the international scientific community. Starting with the Laboratory of Cell Biology in Rome, she went on to found the European Brain Institute. Through her writings and her charities, she supported the cause of education and opportunity for women. She took pride in her civic responsibility as a senator in the parliament of a country that had once rejected her. She died peacefully in her apartment in Rome on December 30, 2012 at the age of 103. Her casket was brought to the Senate of the Italian Republic, where she was honored as “a luminous figure in the history of science, honoring Italy, as well as a symbol of the integration of women in society.”¹⁵ She was buried in the Monumental Cemetery of Turin in the family tomb designed by her brother Gino.

End notes

1. Grazia Deledda received the Nobel Prize in Literature in 1926. The three women who received the Nobel Prize in Physiology or Medicine prior to Rita Levi-Montalcini were Barbara McClintock in 1983, Rosalyn Sussman Yalow in 1977, and Gerty Theresa Cori (born Radnitz) in 1947. See “The Sixty Women Who Have Won the Nobel Prize” (https://stacker.com/history/60-women-who-have-won-nobel-prize) Accessed February 14, 2023.
2. Rita Levi-Montalcini, In Praise of Imperfection: My Life and Work, translated by Luigi Attardi (New York: Basic Books Inc., 1988): 5.
3. Initially Gino and then Rita would add their mother’s maiden name after their father’s death in 1932. Rita’s scientific papers prior to 1938 use “R. Levi”.
4. Marco Piccolino, “Rita Levi-Montalcini’s first intellectual emigration and her research in the laboratory ‘á la Robinson Crusoe’: the letters from Brussels and a ‘Wiggish’ recollection,” Confinia Cephalagica et Neurologica 31, no. 2 (2021): 1-27.
5. The Montalcinis owned the apartment building, and much of the family lived there.
6. A detailed account of the laboratory á la Robinson Crusoe can be found in chapter 10 of In Praise of Imperfection and in reference #3.
7. Viktor Hamburger, “The effects of wing bud extirpation on the development of the central nervous system in chick embryos,” The Journal of Experimental Zoology, 1934, p. 449.
8. W. Maxwell Cowan, “Viktor Hamburger and Rita Levi-Montalcini: The Path to the Discovery of Nerve Growth Factor,” Annu. Rev. Neurosci. 24 (2001): 551-60.
9. In June 1980, at the time of his retirement and eightieth birthday, Viktor gave her a large envelope containing her carefully-preserved onion skin airmail paper letters from Rio.
10. Levi-Montalcini, In Praise of Imperfection, 162.
11. Levi-Montalcini, In Praise of Imperfection, 163.
12. Francesca Valente, Rita Levi-Montalcini: Pioneer & Ambassador of Science (The Mentoris Project, 2021): 170.
13. W. Maxwell Cowan, “Viktor Hamburger and Rita Levi-Montalcini: The Path to the Discovery of Nerve Growth Factor,” 2001.
14. Valente, Rita Levi-Montalcini. See Chapter Twelve, “An Enlightened Attitude Toward Learning” for a fuller exploration of Rita’s writings and opinions on this topic.
15. Valente, Rita Levi-Montalcini, 202.