In turn, the mixture of the humours produces the uniform parts of the body (al-ʾaǧzāʾ al-mutašābiha), such as bones, nerves, muscles or veins. In its normal state, blood is red in colour, has no unpleasant smell, and is sweet to the taste. It is produced in the liver. Phlegm is a whitish discharge that is produced in the liver or in the stomach. The two biles were more hypothetical substances, and generated many disputes about their nature and functions. Yellow bile was generally understood as a foam produced during the formation of blood. It is bright red in colour and is light and pungent. Finally, black bile in its normal state is a sediment of blood, and is refined and bright. Health is understood as a balanced state between the four humours. Disease, on the other hand, can in most cases be explained by the excess of one or several humours, or by the corruption of one or several humours.
Arab physicians inherited the theoretical frame-work of humoral pathology from the Greeks, and especially from Hippocrates’ On the Nature of Man and Galen’s commentary. But they refined this theory in various ways, and also challenged it to a point. Modifications included the potential transformations of the humours into one another as well as the introduction of additional faculties to certain humours. Attempts to challenge humoral pathology remained marginal: for most Arabo-Islamic physicians, humoral pathology should be accepted as a given principle (Gutas 2003, 151). Nonethelesss, these attempts constituted breaches within the overall philosophical framework underlying Islamic medicine…
The Four Humours
According to the prevalent theory of humoral pathology, health results from a balance of the four humours, each of which has two of the four primary qualities, cold or warm, and dry or moist. Yet, there are also contributing factors outside the human body, or, to put it in contemporaneous terms, ‘outside human nature’. These contributing factors are called the six non-naturals (al-ashyāʾ ghayr al-ṭabīʿīya); they are:
1) the ambient air, that is, the environment;
2) food and drink, the things ingested;
3) sleeping and waking;
4) exercise and rest;
5) retention and evacuation, that is, urine, stool, constipation, but also sexual intercourse; and
6) the mental state, such as joy, sadness, fear, elation, apprehension and so on, often inﬂuenced by personal interactions.
The mental states, in particular, were the focus of many physicians’ attention. In the case of certain diseases, music, conversation, and light entertainment could be prescribed. Take melancholy as an example. This disease, caused by an excess of black bile and characterised by despondency, fear and delusions, reacted also to mental stimuli. Avicenna, for instance, recommended listing to music, pleasant conversations with friends, and intercourse with slave girls. In this, he followed a long tradition, going back to the Greek medic Rufus of Ephesus (ﬂ. ca. D 100), who advocated a similar course of action.