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In his article "On the Speed of Mental Processes," Donders explores the relationship between the brain and mental phenomena, examining the known anatomy and anthropology of the brain to conclude that there must be a direct connection between the two. Through experimentation, physiology attempts to locate the various faculties of the mind and trace the nature of the action accompanying mental phenomena. Donders finds that the blood supply is essential for mental processes and that metabolism is at the root of brain life. He also discovers that the blood undergoes a change as it nourishes the brain, including the consumption of oxygen, the formation of carbonic acid, and the generation of heat. Donders posits that this heat may have originated from other forms of energy in the brain, such as electromotive action.