The famous affection of melancholy derives its name to the Greek notion of black bile 
one of the bodily humours that was believed to determine health and disease. The Hippocratic treatise On Human Nature lists black bile alongside blood, phlegm and yellow bile, thus stating a quartet that was destined to have a long career in the history of medicine. But this would not have happened were it not for Galen of Pergamum (129–c.216 CE), who championed the authenticity of On Human Nature (or, to be more precise, its first eight chapters) and its theory of the four humours as innate components of our nature. It should therefore be taken into account by scientific, or philosophical, medicine in relation to the physical qualities and elements. The Hippocratic author associates black bile with two qualities in particular, the cold and the dry, and one of the four seasons in particular, viz. autumn as marked by the predominance of the same qualities. As Stewart points out in this book (a slightly revised Exeter dissertation), Galen has been and still is influential in presenting his particular view on black bile and related diseases, most notably melancholy, as the original Hippocratic one adopted by all the best doctors (e.g. Praxagoras, Diocles, Herophilus and, more recently, Rufus of Ephesus) and philosophers (Plato, Aristotle) after Hippocrates. This is of course just one example of Galen’s general influence on the subsequent interpretation of the history of ancient medicine, his ‘fatal embrace’ as it has been called somewhat dramatically if not inappositely by Vivian Nutton, who also refers to the theory of the four humours as having become the universal standard only after Galen (‘The Fatal Embrace: Galen and the History of Ancient Medicine’, Science in Context, 18 (2005)).
Taking his starting point from a 2009 article by Jacques Jouanna, ‘Bile noire et mélancolie chez Galien,’ in C. Brockmann et al. (eds), Antike Medizin im Schnittpunkt von Geistes- und Naturwissenschaften (2009), Stewart sets out to explore Galen’s theory of black bile, which has so far suffered from relative neglect at the hands of scholars, who have referred to it mainly as part of the four humours schema or dismissed it as incoherent. Thus, Jouanna in the aforementioned article noted two different views on black bile in Galen: a morbid, acidic variety springing from yellow bile that is overcooked (as found in Rufus, whom Galen follows) and an innate humour belonging to our healthy state (in accordance with the Hippocratic Human Nature). Stewart too seems reluctant to speak of an articulated theory. His main contention is that the quest for a systematic theory is self-defeating because it disregards two guiding principles of Galen’s approach: first, there is his bid to present his doctrine as originated by Hippocrates and accepted by a line of good physicians and philosophers leading up to himself. To keep Hippocrates and these other authorities on board, so to speak, Galen has to gloss over differences between them and himself and use loose language in doing so (thus he may speak of ‘black bile’ in cases where, strictly speaking, it is not black bile but what he calls ‘melancholic humour’ at issue).
This is no doubt correct. Far from commending his doctrine as original, Galen presents it as the most recent articulation of a venerable tradition deriving from Hippocrates. Stewart calls this Galen’s ‘doxographic explanation’, a rather unilluminating expression (strictly speaking, ‘doxography’ and ‘doxographic’ refer to a particular genre of compilations of doctrines, viz. the Placita tradition reconstructed by Hermann Diels and, more recently, Jaap Mansfeld and David Runia on the basis of extant specimens; the term was coined by Hermann Diels by analogy with ‘biography’, which does have an ancient counterpart). The practice of grounding one’s position in an authoritative tradition and so in the ‘ancient account’ 
was typical of Galen and his age. It is often found in conjunction with the second point to which Stewart draws our attention: the fact that Galen’s statements and arguments concerning black bile are determined by their particular, often polemical, context and so by the particular adversary or adversaries whom he takes as his butt. Against them he plays off the grand tradition of good medicine and philosophy. Galen, Stewart argues, is particularly concerned to refute the medical scientists Erasistratus of Keos (first half of third century BC) and Asclepiades of Bithynia (active in the first half of the first century BC) as having ignored the existence of black bile and its crucial role in health and disease. This polemical attitude may lead to apparent and sometimes real inconsistencies, at least if one tries to build a coherent doctrinal system out of Galen’s disparate statements, even within one and the same treatise. This too is a salutary reminder: dialectical context does matter a lot in Galen, as in other ancient authors.
Stewart feels able to distinguish between three varieties of ‘melancholic humour’, starting from On Affected Parts III, 9 (pp. 75–92). Here, Galen subsumes under the generic heading of ‘melancholic humour’: (1) black bile in the strict sense, which arises naturally from our bodily mixture or the process of digestion – it is therefore beneficial, but may turn pathological under certain conditions such as combustion; (2) the sediment of blood, lees-like or mud-like, which he calls melancholic blood or ‘melancholic humour’ in a specific sense – it is natural too, but when altered or displaced can cause such diseases as melancholy; (3) an acidic, thinner form of black bile that results in the extreme heating of the humours and of yellow bile in particular, unnatural and harmful and often fatal. What these three forms have in common is that they are defined by the pairing of the cold and dry qualities, as black bile is in ‘Hippocrates’. Stewart calls these three forms ‘ideal natural black bile’, ‘non-ideal natural black bile’ and ‘altered black bile’ respectively (see pp. 92–3). In these terms, Stewart goes on to discuss how harmful black bile arises, how it may be cleansed (with particular reference to the role of the liver and the spleen) and which diseases are attributed to black bile or ‘melancholic humour’ (chapters 5–7). Stewart persuasively argues that Galen needs the above distinction because he wants to dissociate the illness of melancholy from natural black bile. But, as we have noticed, he also argues that Galen does not always apply a strict nomenclature. This may certainly be explained as loose usage for reasons of a strategic kind. In another key passage, Black Bile 8, pp. 93.22–28 (quoted by Stewart on p. 78), Galen himself says as much with respect to the expression ‘melancholic humour’, in line with On Affected Places III, 9. Even so, a lot is made to depend on the passage from the latter work. Not everything falls into place by applying the trifold distinction drawn there, e.g. quartan fevers seem to be due to both types (2) and (3) (pp. 136–42). Given the importance of context, Stewart notes in the general conclusion, it remains difficult to summarise the analysis of Galen’s account of black bile on the basis of a single comprehensive framework (p. 149). But this makes it all the more useful to have this careful discussion focused on black bile and based on so many relevant passages from Galen’s vast corpus of writings.
