Abstract: The movement and stretching behavior of experimental animals, which is significant in different tests of the effect of drugs, is rendered objectively analyzable by the photoelectric conversion of the shadow of the animal into an electric signal. The shadow of the animal is projected onto a photoelement (4) forming a projection surface. The signal generated by the photo-element-projection surface (4) is conducted by means of a current/voltage converter (5) to an aplifier (6). The amplified signal (S) is passed on the one hand to a recorder (7) and on the other through an amplitude threshold value detector (8) and a time interval threshold value detector to a counter (9). The threshold values are set in a manner such that the counter counts only the significant stretchings of the experimental animal.