Michael Bresalier, <i>Modern Flu: British Medical Science and the Viralisation of Influenza, 1890–1950</i> London: Palgrave Macmillan, 2023. Pp. xxvii + 458. ISBN 978-1-137-33953-9. £95.00 (hardcover).

Influenza is a virus.Of its four genera, three infect humans (influenza A, B and C).How did we come to 'know' this?This is the question that Michael Bresalier aims to answer in his wonderful new book.Bresalier argues that although the biological truth that influenza is a viral disease is an ancient reality, 'medical and scientific knowledge of influenza is historically recent, contingent on and contextualized through developments from the late nineteenth century to the 1940s' (p.5).Modern Flu seeks to centralize British laboratory science in how we have come to 'know' the viral nature of influenza.Influenza provides Bresalier with an important historical example of the 'alignment and integration of virological knowledge with existing epidemiological, clinical, and pathological knowledge' which he argues was 'integral to creating the identity of a viral disease' (p.20).Bresalier carefully guides the reader through a series of pivotal moments in the history of influenza research.He argues that before the twentieth century, the medical understanding of influenza was highly protean.Influenza was little more than 'a plethora of respiratory, nervous, or gastral symptoms' (p. 1).After a contextual chapter on nosology in the eighteenth and early nineteenth centuries, Bresalier traces the origins of 'modern' flu to the 1889-94 influenza pandemic, during which medical scientists established a 'modern' identity for the disease, constructed from bacteriological, clinical and epidemiological knowledge.That identity was ultimately wrongcontemporaries misattributed the cause of flu to the bacterium Bacillus influenzae (Pfieffer's bacillus)but Bresalier sees this as an important moment in modernizing flu, establishing an identity for influenza that was 'cause-based' rather than 'symptom-based' (p.104).Bresalier then shows how collaboration between the Army Medical Service and the Medical Research Council (MRC) during the 1918-19 pandemic broke the stranglehold of Pfieffer's bacillus yet created new uncertainties about the disease's nature.'The pandemic had ignited interest in the possible role of a filterable virus and the general nature of such agents, yet the way forward was unclear ' (p.162).Bresalier examines how the MRC sought in the 1920s to 'transform viruses into workable laboratory objects and to develop new methods for their control ' (p.162).Flu was at the centre and the pandemic was the catalyst.Research on a different virus, canine distemper, at the National Institute for Medical Research (NIMR) laid the foundations for influenza virus research, but the inability to identify the virus left flu as protean as ever.It was not until 1933, when a team of scientists working at the NIMR 'joined physicians and pathologists in a crucial series of studies on influenza', used ferrets as a proxy for humans, and at last brought influenza 'within