The authors of this book have taken on the challenging task of tracking the origins, rise and eventual demise of the concept of ‘animal spirits’ over nearly two and a half thousand years. It was not until well into the nineteenth century that the doctrine finally dropped out of use as a newer paradigm came to the fore, one in which the modern discipline of neurophysiology gradually took shape. To provide an overall framework for this narrative, the book is divided into five historical periods, starting with the ancient Greeks to Galen, followed by a section on early Christian and Islamic treatments of the doctrine, which the authors argue are rarely considered in historical overviews of scientific development that pass over the ‘Dark Ages’ to the dawn of the Renaissance. The remaining sections encompass the Scientific Revolution (‘The doctrine questioned’) and the Enlightenment (‘The doctrine in retreat’), and conclude with a section on ‘The doctrine discarded’ that goes back to 1600 and ends in the mid-twentieth century because it traces the early history of electricity and its eventual linkage with the nervous system as experimental physiologists gradually came to understand the nature of nerve action in electrical terms. Presumably because it is targeted more at a general audience than at professional historians, the book includes maps and timelines to help orient the reader, and the story is told chiefly through the biographies of its key protagonists.

As the early part of the book makes clear, the concept of animal spirit or spirits emerged in the context of fundamental discourses about the nature of life, the universe and everything, including the existence of deities and their relationship with mankind. The authors pay close attention to the early Greek categories of psyche and soma (which broadly translate as ‘soul’ and ‘body’), linked as they were by pneuma (breath), the self-moving substance or fluid that eventually became Latinized as spiritus, or spiritus animalis, and which in turn was understood to mediate between anima and corpus. Galen's model of the nerves (i.e. as hollow tubes through which the wind-like animal spirits flowed and acted as the agent for sensation and motion) proved compatible with the Christian doctrine of the immaterial soul, a link which in part accounts for its longevity in the Western medical tradition and also gives rise to a tension within the book. On the one hand the authors express a view that readers of this journal may question, namely that religion has mostly ‘held back’ scientific progress, and that neurophysiology only properly advanced once it was separated from metaphysics. On the other hand, they spend a lot of time exploring the fruitful contamination between different kinds of spirit, and plainly demonstrate the striking extent to which research into nerve action has been linked to broader discourses about the animating principle of the universe and even the nature of divinity itself.

For example, one of the pivotal figures in this book proves to be Newton, who postulated the existence of a subtle, vibrating aether that permeates the entire cosmos and acts as the medium for light, gravity and also electricity, a material substance which he thought might also account for sensation and motion by means of its rapid vibrations within the solid nerves. By the nineteenth century the animal spirit concept ‘grudgingly gave way to the idea that the nerves and muscles function electrically’ (p. 203), a paradigm shift which meant that Newton's neurophysiology can be seen by the authors as ‘the first coherent successor theory to the ancient hydrodynamic model’ (p. 149). Although glossed over here, however, Newton also suggested that this electrical medium served as God's sensorium, the instrument for His actions in the universe. In other words, holding a ‘materialist’ theory of nerve action and mental functioning was not incompatible with a belief in the Deity and the existence of souls, even though the authors keep trying to make this point. That this was still the case in the nineteenth century is shown, for example, in L.S. Jacyna's ‘The physiology of mind, the unity of nature, and the moral order in victorian thought’ (BJHS (1981) 14(2), 109–132).

For a general audience, including readers who are abreast of the neurosciences, there is much to learn from this book. It is written in an engaging style, making accessible often complex and also competing theories from the past about how the nerves function. One of its strengths is its use of primary material, which is quoted extensively and translated where appropriate, although the original texts are not provided alongside the translations. As well as focusing on major figures (e.g. Galen, Descartes, Haller, Galvani, Helmholtz), the authors pay attention to the ideas of less familiar individuals (e.g. Stensen, Croone, Swedenborg, Bernstein) in each period. However, professional historians may well react negatively to the way that the authors portray their discipline as a model of scientific progress once the dead hand of the animal spirit doctrine was finally lifted. As they rightly say, there are many ways that their story could have been told, and they have raised some intriguing questions yet to be answered. For example, could the way that the term ‘animal spirits’ dropped out of medical discourse over a relatively short period in the early nineteenth century (p. 243) be compared to the shift that Thomas Dixon, in From Passions to Emotions: The Creation of a Secular Psychological Category (2003), found taking place over the same period? For while the animal spirits constituted the vehicle of the passions, the emotions have been more associated with nervous electricity. Perhaps the authors can now be persuaded to follow Jacyna's example and track the relationship between physiology and psychology once the animal spirits no longer served as their intermediary?