According to the medieval medical concept, ultimately going back to Galen, memory is a psychical faculty located in the posterior ventricle of the brain. When this faculty is affected by a disturbance of the balance of the four bodily humours, i.e., by too much moisture and/or coldness of the brain, forgetfulness will be the result. One way to treat this affliction is to restore the humoral balance by administering warm drugs. A popular but also notorious drug for forgetfulness was balādhur (Semecarpus anacardium L; marking-nut), indigenous in India, and called by the Arab physicians ‘ḥabb al-fahm’ (nut of apprehension). The popularity of the marking-nut is sometimes explained from the fact that its juice when exposed to the air turns into a black corrosive fluid which was used as an indelible ink for marking linen and woollen clothes. Another explanation is that the nut has the shape of a heart, cf. the Latin ‘anacardia’ and the Arabic epithet ‘ḥabb al-qalb’. The black, resinous, viscid and acrid juice of the nut is called ‘honey’ by the medieval physicians; it is, according to them, hot and dry in the fourth degree and is recommended for a variety of diseases, but above all forgetfulness.