THE GEOTROPIC CONDUCT OF YOUNG GUINEA PIGS.

Young guinea pigs while progressing on an inclined surface orient upward in a way such that the path of progression is at a mean angle theta to the intersection of the plane with the horizontal. The angle theta increases as the angle alpha of the inclination of the plane increases. The results of this experiment indicate that in principle the formulation of similar behavior in the cases of young rats and mice holds essentially for young guinea pigs, and further supports a general muscle tension theory of the limitation of geotropic orientation. The relation of theta to log sin alpha is sigmoid in character and cos theta is a nearly rectilinear function sin alpha. It is notable however that in this case the functions are in reality compound, being made up of two curves with a break occurring at a slope of alpha = 45 degrees . Observation of a blinded guinea pig in light upon an inclined plane reveals the fact that in the neighborhood of 45 degrees the mode of progression changes. Below this angle the animal walks with the feet on the two sides of the body moving forward alternately, while above alpha = 45 degrees the animal hops in such a way that both front feet and both hind feet move forward together. This change in the mode of progression clearly involves a change in the organization of muscular tensions, and in all probability accounts for the change in the relation of the values of theta to the magnitudes of the slope. The behavior of the mean theta's is closely paralleled by that of their P.E.'s, an automatic check being in this way given upon the significance of the measurements.