I have hitherto described results obtained with the Method of Axial Rotation; I shall now take up the second method, that of Vertical Rotation, diagrammatic representation of which is given in figure 166V. The specimen is held vertical and two electrical contacts, A and B, made with the two lateral sides; it is then rotated round a horizontal axis perpendicular to the length of the specimen. Rotation may be carried in a right-handed direction with increasing angle with the vertical. The point A is thus subjected to enhanced geotropic stimulation and exhibits increasing electric change of galvanometric negativity; continuous decrease of angle of inclination to zero by rotation in the reverse direction causes a disappearance of the induced electric change. The rotation is next continued in the negative direction by which the point B is increasingly subjected to geotropic action. B is now found to exhibit excitatory reaction, the current of response having undergone a reversal. Rotation to the right and left will be distinguished by plus and minus signs. ELECTRIC RESPONSE THROUGH AN ENTIRE CYCLE. _Experiment 177._--When the specimen is vigorous, characteristic response with its changing sign may be obtained through an entire cycle from 0° to +45° to +90°; then back to 45° to 0° to -45° to -90°. With less vigorous specimens the responses becomes enfeebled under fatigue. I give below the results of a typical experiment carried out with a vigorous specimen, the response being distinguished as - when A is above, and + when A is below, the inversion bringing about a reversal direction of the responsive current. +------------------------------------------------------+ |Angle of inclination |+45°|+90°|+45°| 0°|-45°|-90°| |-------------------------+----+----+----+---+----+----| |Galvanometer deflection |-19 |-35 |-18 | 0 |+14 | +25| +------------------------------------------------------+ RELATION BETWEEN ANGLE OF VERTICAL ROTATION AND INTENSITY OF GEOTROPIC REACTION.