METHODS

TWO different groups of animals have been used. One group consisted of young albino rats weighing from 90 to 110 gm. at the time of operation. The other group was made up of rats definitely past the age when sex maturity appeaw: the females weighed about 175* a. and the males over 250 gym. when operated. All animals of the series were operated under Evipal (0.1 gin. per kilogram of body weight) anesthesia. Lesions were placed in the hypothalamus by the Horsley-Clarke technic, employing Clark's ('39) modification of the stereotaxic instrument which enables one to use the apparatus on rats. S o chart series of the rat hypothalamus has as yet been made; and since a separate chart series would be necessary for each new variation in weight-range it has been found more practical to deteriiiine any desired set of Horsley-Clarke coordinates by operating a couple of animals of a given size and examining the lesions macroscopically at once. Following this practice we have in all rats selected coordinates which would