Analysis of the Geotropic Orientation of Young Rats. Vi

The result of crossing two well-inbred lines of organisms for each of which there has been established by repeated test a characteristic relationship between some aspect of performance or behavior and a measured external condition governing the performance, is important in at least two respects. I t should contribute to the demonstration of the degree of reality inhering in the formulation used to express the characteristic relationship in point, and thus by implication at least to provide interpretation for it; constants in equations must be accorded physical significance if they can be shown to exhibit unitary behavior in inheritance. Conversely, the genetic utilization of such constants should provide rational, serviceable units of inheritance,J a means of really defining a gene 1 (cf. Crozier and Pincus, 1929-30, a). A first illustration of primitive steps in the technic of such experiments has been given in the treatment of the geotropic orientation of young rats (Crozier and Pincus, 1929-30 a; 1929-30, b; 1931-32, a, b). Essential additional features of such experiments (cf. also: Crozier, 1929; Crozier, Stier, and Pincus, 1929; Pincus, 1930-31; and Crozier and Pincus, 1931-32, a) are: the establishment of the connection between intensity of excitation, or of a condition controlling performance, and the measured response, for single individuals over a range of values of the experimental variable; the analytical description and utilization of the variability of performance; and the provision of