Baglivi published in Perugia, for the first time in 1700, his reflections about the fibers as fundamental parts of the living organisms. The text, conceived as a letter to Alessandro Pascoli, underlines the role of the cerebral membrane in physiological and pathlogical phenomena. The Specimen quatuor librorum de fibra motrice et morbosa has been printed in 1702 as an answer to the book of A. Pacchioni De durae matris fabrica et usu. Living fibres are the fundamental structural elements making up the human body and the living organisms, seats of the vital functions and main causes of diseases. In formulating the living fibers theory, Baglivi places himself as a first bridge between classical medicine and the reductionist method of natural sciences.