The behavioral changes ascribed to bilateral removal of the amygdala and piriform lobe, especially "angry" behavior, has been restudied in 13 cats. Excision of this region was proved in 9. While observed for periods of 6 months to more than 1 year, no state of intractable savageness replaced previously normal tame behavior. Indifference to the presentation of live mice was a curious behavioral deviation in 11 animals, in striking contrast to their preoperative responses. Two animals with incomplete removals became moderately hostile to observers after several months, as indicated by hissing and growling; however, despite such unfriendly demonstrations they could be handled with impunity. The only significant histological difference between these and the unchanged animals was damage to the ventrolateral portion of the hypothalamus on one side. Whether this could be pertinent requires further experimentation, but a possibility of bilateral functional derangement from this type of lesion remains.

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