ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. VIII

The upward geotropic orientation (angle theta) of adult rats (race A) has been measured as a function of slope of substratum. The relative variation of orientation angle is a declining rectilinear function of theta. The fraction of the total observable variation of performance (theta) which is controlled by the intensity of excitation (56 per cent) is identical with that found for young rats of the same strain, although the total variation is a little greater. Injection of adrenin distorts the theta vs. alpha graph in a manner quite concordant with the effect obtained in young rats. With the adults the absolute magnitudes of the variations of theta, at corresponding intensities of excitation, are not affected by the action of adrenin, and, as with the young, the proportion of modifiable variation of theta is not altered. The variability of performance, considered as a function of the performance, must therefore be regarded as an organic invariant. Certain consequences of this finding are referred to.