The story of a friendly relationship between two great scientists, Gregorio Marañón (G.M.) and Walter B. Cannon (W.B.C.), is reported. Both share a common interest for the biology of emotion. In the early twenties they had already made important contributions to the nature of the emotional processes. The meeting point was in the interpretation of the somato-visceral response elicited by the injection of adrenaline in humans (G.M.) and of the emergency reaction (W.B.C.). The relevant moment in their relationship was the utilization by W.B.C. of the G.M.'s results concerning the artificial induction of the visceral changes typical of strong emotions as the main argument against the James-Lange theory of emotion, as no specific emotion was generated by the adrenaline; instead, only "as if" subjective feelings were reported by patients. A clear distinction then was drawn by G.M. between perception of the vegetative changes and the physical emotion proper. Since then it was clearly defined the cognitive component as essential and primary as concerns to the nature of emotion. The visceral changes are not determinant of the emotional quality. Its role was restricted to the strength and duration of the emotional experience.