ITMP. July, 2013; No. 1, Vol. 1 Available at: http://itmp.tums.ac.ir 15 JOURNAL OF IRANIAN TRADITIONAL MEDICINE AND PHARMACY The structure of vital spirit through Avicenna's Canon on Medicine and its similarity to electricity F. Amini Behbahani a , H. Emamdjomeh b , E. Nazem a , M. Keshavarz *a,c a School of Traditional Medicine. Tehran University of Medical Sciences, Tehran, Iran b Rasoul Akram Hospital, Department of Research center of ENT & Head & Neck Surgery. Tehran University of Medical Sciences, Tehran, Iran c Department of physiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran * Corresponding author at: Department of Histology , School of Medicine, Tehran University of Medical SciencesTehran, Iran E-mail address: mkeshavarz@tums.ac.ir Abstract For describing structure and quality of spirit in traditional medicine sources and achieving a common language between today and past knowledge, we search traditional medicine sources in Islamic era (dark ages in European history). In this way Avicenna's notes was our main source. This study presents a comparison between some spirit replacement candidates and spirit characteristics in Canon on Medicine. Traditional medicine in Islamic era follows both ancient Egyptians' belief in immortal soul and Aristotle's belief in material quality of soul. Islamic scientists divided it to two parts. Material part (known as medical spirit) acts as a connector of immortal part (soul) to body. This material part initially is produced in heart and is known as vital spirit. That is origin of other spirits. Similarity of vital spirit to heart electrical activities is more prominent than the other equal candidates. This can leads us to a new understanding of spirit. Keywords:spirit – traditional medicine – Unani medicine – Avicenna – vital spirit