Holly Hill is one of Hampstead's most secluded streets — a steep, narrow lane that climbs from the bustle of Heath Street toward the quieter reaches of the village, passing the Friends Meeting House and a row of handsome Georgian cottages before reaching the summit at Mount Vernon. The houses here are discreet and well-maintained, their gardens shaded by mature trees, and the general atmosphere is one of cultivated privacy. Nothing about the street suggests that it was once the site of one of the most important scientific laboratories in the world — a place where pioneering research into viruses, bacteria, and the mechanisms of immunity laid the foundations for modern medicine and contributed to the saving of millions of lives.
The National Institute for Medical Research occupied the Mount Vernon site from 1914 to 1950, a period that spanned two world wars, the worst pandemic in recorded history, and a revolution in the understanding of infectious disease. During those thirty-six years, the institute's scientists conducted research of extraordinary range and significance — from the isolation of the influenza virus to the development of new vaccines, from the study of bacterial genetics to the exploration of the chemical basis of immunity. The work done on Holly Hill attracted some of the finest scientific minds of the twentieth century, produced multiple Nobel Prize winners, and established a tradition of publicly funded medical research that continues to shape British science to this day.
The Founding of the Institute
The National Institute for Medical Research was established in 1913 as part of the Medical Research Committee (later the Medical Research Council), a body created by the National Insurance Act of 1911 to coordinate and fund medical research in Britain. The act, one of the landmark achievements of Lloyd George's Liberal government, recognised that the nation's health depended not merely on the provision of medical treatment but on the systematic investigation of the causes and mechanisms of disease. The creation of a dedicated research institute was the practical expression of this recognition — a statement that medical science deserved the same kind of institutional support that the nation provided for its universities, its museums, and its military.
The choice of the Mount Vernon site was not accidental. The building — a substantial Victorian house that had previously served as a hospital — offered the space, the privacy, and the distance from the noise and pollution of central London that laboratory research required. The Hampstead location also placed the institute within easy reach of the capital's medical schools and teaching hospitals, facilitating the exchange of ideas and personnel between clinical practice and basic research. The proximity of Hampstead Heath, with its clean air and open spaces, was an additional attraction in an era when tuberculosis and other respiratory diseases were still major killers and when the benefits of fresh air and elevation were taken seriously by the medical profession.
The institute's first director was Sir Henry Dale, a pharmacologist whose work on the chemical transmission of nerve impulses would eventually earn him the Nobel Prize in Physiology or Medicine in 1936. Dale was a scientist of exceptional breadth and rigour, equally comfortable in the laboratory and in the committee room, and he brought to the institute a vision of medical research that combined the highest standards of experimental technique with a practical concern for the application of scientific discoveries to the prevention and treatment of disease. Under his leadership, the Mount Vernon laboratory attracted a team of researchers whose collective achievements would transform the understanding of infectious disease.
The early years of the institute were dominated by the practical demands of the First World War. The conflict generated medical problems on a scale that no previous war had approached — wound infections, gas gangrene, tetanus, trench fever, and the devastating effects of chemical weapons — and the institute's scientists were mobilised to address them. Research into wound bacteriology, antiseptics, and the treatment of gas injuries produced results that saved lives on the Western Front and advanced the understanding of infectious disease in ways that would bear fruit for decades after the war's end.
The 1918 Influenza Pandemic
The catastrophe that defined the institute's early history and shaped its subsequent research programme was the influenza pandemic of 1918-1919 — the so-called "Spanish flu" that killed an estimated fifty million people worldwide, more than the total combat deaths of both world wars combined. The pandemic struck with terrifying speed and lethality, killing young and healthy adults as readily as the elderly and the infirm, and overwhelming the medical systems of every country it touched. In Britain, the pandemic killed approximately 228,000 people, and its effects were felt with particular severity in the crowded cities where the virus spread most easily.
The scientists at Mount Vernon were among the first to attempt a systematic investigation of the pandemic. The challenge was formidable. The causative agent of influenza was unknown — the very concept of a virus, as distinct from a bacterium, was still poorly understood, and the laboratory techniques required to isolate and study viral agents were in their infancy. Many researchers believed that influenza was caused by a bacterium, Haemophilus influenzae (also known as Pfeiffer's bacillus), which had been isolated from influenza patients during an earlier pandemic in 1892. The Mount Vernon scientists undertook a rigorous investigation of this hypothesis, examining clinical samples from pandemic victims and attempting to reproduce the disease in laboratory animals.
Their findings were inconclusive — the bacterial hypothesis could neither be confirmed nor definitively ruled out — but the work established the methodological framework within which the influenza problem would eventually be solved. The recognition that the causative agent of influenza might be too small to be seen under a conventional microscope and too small to be trapped by the filters used to separate bacteria from liquid cultures pointed toward the concept of a "filterable virus" — an agent so tiny that it could pass through barriers that would stop any known bacterium. This concept would prove to be the key to understanding influenza and a host of other diseases, and it was the scientists at Mount Vernon who, through their painstaking and often frustrating investigations, helped to bring it into focus.
The pandemic also demonstrated the urgent need for better understanding of respiratory diseases in general. The Mount Vernon institute emerged from the pandemic with a renewed commitment to virology — the study of viruses — and this commitment would drive its research programme for the next three decades. The pandemic had shown that infectious diseases could overwhelm even the most advanced medical systems, and that the only reliable defence was scientific understanding of the agents that caused them. This lesson was not lost on the institute's leadership, and the investment in viral research that followed would produce results of incalculable value.
Pioneering Viral Research
The breakthrough that established the Mount Vernon institute's international reputation came in 1933, when a team of scientists led by Wilson Smith, Christopher Andrewes, and Patrick Laidlaw succeeded in isolating the human influenza virus for the first time. The achievement was the culmination of years of patient experimental work, and it depended on a combination of scientific insight, technical innovation, and a measure of good fortune.
The critical innovation was the use of ferrets as experimental animals. Laidlaw, who had been studying distemper in dogs and ferrets, observed that ferrets were susceptible to a respiratory infection that closely resembled human influenza. When throat washings from human influenza patients were introduced into the nasal passages of ferrets, the animals developed symptoms — fever, nasal discharge, lethargy — that precisely mimicked the human disease. The filtrates from these infected ferrets, when passed through bacteria-proof filters, retained their ability to cause disease, confirming that the causative agent was a virus rather than a bacterium. The human influenza virus had been identified at last.
The significance of this discovery was immense. For the first time, scientists had an animal model in which the influenza virus could be studied under controlled laboratory conditions. This opened the way for systematic research into the virus's biology, its mechanisms of transmission, its genetic variability, and — most importantly — the development of vaccines against it. The isolation of the influenza virus at Mount Vernon was the foundation on which all subsequent influenza research has been built, from the development of the first influenza vaccines in the 1940s to the ongoing global surveillance programme that monitors the emergence of new influenza strains and guides the annual formulation of seasonal vaccines.
The ferret model also provided an unexpected bonus. Wilson Smith, one of the three scientists who isolated the virus, contracted influenza from a ferret in the course of the experiments — one of the earliest documented cases of reverse zoonotic transmission from a laboratory animal to a human. The incident confirmed the identity of the viral agent and provided the first human-derived viral isolate, which was preserved and used in subsequent research. Smith's illness, though unpleasant, was a contribution to science that he bore with characteristic good humour.
Nobel Prize Winners
The Mount Vernon laboratory was a nursery of Nobel Prize-winning talent. Sir Henry Dale, the institute's first director, received the Nobel Prize in Physiology or Medicine in 1936 for his discoveries relating to the chemical transmission of nerve impulses. Dale's work demonstrated that nerve signals were transmitted across synapses not by electrical impulses alone, as had previously been believed, but by chemical substances — neurotransmitters — that were released from the nerve endings and acted on receptors in the target cells. This discovery was fundamental to the understanding of the nervous system and opened entirely new fields of pharmacological research.
Dale shared the 1936 Nobel Prize with Otto Loewi, an Austrian pharmacologist whose complementary experiments had confirmed the chemical nature of neurotransmission. The collaboration between Dale and Loewi — conducted across national boundaries, in different laboratories, using different experimental approaches — was a model of international scientific cooperation, and it demonstrated the value of the kind of basic research that the Mount Vernon institute was designed to support. Dale's neurotransmitter work was not directed toward any immediate medical application — it was driven by pure scientific curiosity about the mechanisms of nerve function — but its practical consequences were enormous, leading to the development of drugs for the treatment of conditions ranging from depression to Parkinson's disease to myasthenia gravis.
Sir Peter Medawar, who worked at the institute during the 1940s and would later serve as its director at the Mill Hill site, received the Nobel Prize in Physiology or Medicine in 1960 for his discovery of acquired immunological tolerance. Medawar's research demonstrated that the immune system's ability to distinguish between "self" and "non-self" — between the body's own tissues and foreign material — was not entirely innate but was partly learned during embryonic development. This discovery was transformative for the field of organ transplantation, providing the theoretical foundation for the immunosuppressive techniques that would eventually make transplant surgery a practical reality.
The concentration of Nobel-calibre talent at Mount Vernon and its successor at Mill Hill was not coincidental. The institute's research culture — its emphasis on basic science, its tolerance of long-term investigations that might not yield immediate results, its willingness to support researchers who followed their curiosity wherever it led — created an environment in which exceptional work was not merely possible but expected. The institute attracted scientists who were drawn by the freedom to pursue fundamental questions without the pressure to demonstrate short-term commercial value, and this freedom, paradoxically, produced results of immense practical importance.
The Building's Architectural History
The Mount Vernon building that housed the National Institute for Medical Research had a history that predated its scientific incarnation by several decades. The original house on the site was a substantial Georgian villa, built in the late eighteenth century as a gentleman's residence on one of Hampstead's most elevated and desirable streets. The house commanded views across the Heath to the spires of the City, and its gardens, terraced into the hillside, enjoyed the clean air and abundant light that made Hampstead a favoured location for those who could afford to live above London's smoke.
In the nineteenth century, the property was converted into a hospital — the Mount Vernon Hospital for Consumption and Diseases of the Chest, which treated patients suffering from tuberculosis and other respiratory conditions. The choice of Hampstead for a tuberculosis hospital was logical: the elevation, the fresh air, and the proximity of the Heath provided exactly the environmental conditions that Victorian medicine considered essential for the treatment of lung disease. The hospital's patients could sit in the garden, breathing the clean hilltop air, while looking down on the smoky city that had made them ill.
When the hospital moved to a larger site in Northwood, Middlesex, the Mount Vernon buildings became available for repurposing, and the Medical Research Committee seized the opportunity to establish its new institute in premises that were already equipped for medical use. The conversion from hospital to laboratory required extensive modifications — the installation of autoclaves, incubators, centrifuges, and the specialised ventilation systems required for work with infectious agents — but the basic structure of the building, with its large, well-lit rooms and its generous circulation spaces, proved well suited to its new function.
The building's architecture, though not distinguished by the standards of Hampstead's Georgian heritage, had a solid, dignified quality that suited its scientific purpose. The entrance hall, with its tiled floor and substantial staircase, gave an impression of institutional permanence. The laboratories, with their high ceilings and large windows, provided the light and air that microscopy and chemical analysis demanded. The gardens, which had once served the therapeutic needs of tuberculosis patients, now served the recreational needs of scientists who spent their days in the focused concentration of laboratory work and needed, in their breaks, the restorative effects of fresh air and green space.
The Move to Mill Hill
By the late 1930s, it had become clear that the Mount Vernon site could no longer accommodate the institute's expanding research programme. The building was too small, its laboratories too cramped, and its facilities too outdated to support the increasingly sophisticated experimental work that modern biomedical research demanded. The decision to relocate was taken before the Second World War, and a new purpose-built laboratory was constructed on a site at Mill Hill, in the London Borough of Barnet, that offered the space, the facilities, and the security that the institute's work required.
The move to Mill Hill was completed in 1950, bringing to an end thirty-six years of scientific activity on Holly Hill. The relocation was a practical necessity, but it was also an emotional wrench for those who had worked at the Hampstead site. The intimacy of the Mount Vernon laboratory — its village setting, its proximity to the Heath, its compact scale that encouraged collaboration and the informal exchange of ideas — could not be replicated in a larger, more dispersed institution. Several of the institute's senior scientists noted that the move to Mill Hill, while essential for the future of the research programme, entailed a loss of the particular atmosphere that had made Mount Vernon a place where ideas could germinate in the spaces between formal experiments, in chance encounters on the stairs and conversations over lunch in the garden.
The Mill Hill laboratory would go on to an illustrious history of its own, continuing and extending the research programmes that had been initiated at Mount Vernon. The influenza work continued, producing new insights into the virus's behaviour and contributing to the development of improved vaccines. Medawar's immunological research, begun at Mount Vernon, reached its Nobel Prize-winning culmination at Mill Hill. New fields of research — molecular biology, structural biology, neuroscience — were added to the institute's portfolio, and the Mill Hill laboratory became one of the most productive biomedical research centres in the world.
The institute's eventual closure in 2015, when its remaining research groups were transferred to the Francis Crick Institute in central London, marked the end of a century-long tradition of publicly funded medical research that had begun on Holly Hill in 1914. The closure was controversial — many scientists argued that the dispersal of the institute's research groups would destroy the collaborative culture that had been its greatest strength — but the decision reflected the broader trend toward large, centralised research facilities that characterised early twenty-first-century science policy.
Legacy in NW3 Science
The Mount Vernon building still stands on Holly Hill, converted now to residential use, its scientific history invisible to the casual observer. No plaque marks the spot where the influenza virus was first isolated. No memorial records the Nobel Prize-winning research that was conducted within its walls. The building has been absorbed back into the domestic fabric of Hampstead, its laboratories transformed into living rooms, its garden returned to private use, its contribution to human welfare preserved only in the scientific literature and in the memories of those who worked there.
Yet the legacy of the Mount Vernon institute pervades the intellectual culture of NW3 in ways that are less visible but no less real. The presence of a major research laboratory in Hampstead during the first half of the twentieth century reinforced the neighbourhood's identity as a place of serious intellectual endeavour — a place where the life of the mind was not confined to the arts and humanities but extended to the natural sciences as well. The scientists who lived and worked in Hampstead during the Mount Vernon years were part of the same intellectual community that included the writers, the psychoanalysts, the philosophers, and the political thinkers who gave the neighbourhood its distinctive character. They attended the same concerts, frequented the same pubs, walked the same paths across the Heath, and participated in the same culture of informed, curious, analytical engagement with the world that has always been Hampstead's greatest asset.
The institute also contributed to the development of the broader scientific infrastructure of North London. The Hampstead area's association with medical research did not end with the institute's departure — the Royal Free Hospital, the Tavistock Clinic, the Anna Freud Centre, and numerous smaller research institutions have maintained a tradition of scientific and clinical investigation that owes something to the precedent established at Mount Vernon. The idea that Hampstead is a place where serious research is conducted, where the boundaries of human knowledge are pushed forward, and where the welfare of society is advanced through disciplined inquiry — this idea has its roots in the modest laboratory on Holly Hill where, in the early decades of the twentieth century, a small group of scientists changed the world.
The story of the National Institute for Medical Research at Mount Vernon is, in the end, a story about the value of sustained investment in basic science. The research conducted on Holly Hill was not driven by commercial imperatives or immediate practical needs — it was driven by curiosity, by the desire to understand the natural world, and by the conviction that understanding, once achieved, would find its practical applications in due course. This conviction was vindicated spectacularly. The isolation of the influenza virus, the discovery of neurotransmitters, the elucidation of immunological tolerance — these were achievements of pure science that transformed the practice of medicine and saved countless lives. They were achieved in a quiet laboratory on a quiet street in Hampstead, by scientists who worked without fanfare, without celebrity, and without the prospect of personal wealth, sustained only by the intellectual excitement of discovery and the knowledge that their work mattered. Their legacy deserves to be remembered, and the building on Holly Hill where they worked deserves a plaque.
*Published in the Hampstead Renovations Heritage Collection — exploring the architecture, history, and stories of London's most remarkable neighbourhoods.*