Sincethe "Paragone" of the 16^th c. the theoreticians of art emphasized the importance of the sense of touch for the per­ception of sculptural works. Nevertheless, there is yet no summarized treatise dealing with the problem of tactile perception in the history of art. The article "The Fifth Brother" (the title relates to Jacopone da Todi's allegory of the sense of touch) states the close relationship between the tactile approach of the connoisseur and the frequent literary theme of the sexual intercourse with a seductive statue in Renaissance and Baroque; it describes the beginnings of today's "Do not touch" attitude in museums; and it deals with the new ideal of the observer, emerged in the second half of the 18^th c. In this context, above all, the role of the sense of touch in the writings of Winckelmann, Herder and Heinse will be discussed.