Intense emotion, especially fear, is one of the most injurious of human experiences. In fact, fear may be defined as the typical emotion, since practically every emotional state is allied to it, even anger, which must have originated in the impulse of self-protection against threatened danger. In the hope of discovering which organs participate in the production of fear, and the role assumed by each, I began a research to this end in 1908, the earlier results of which were reported in the Ether Day Address at the Massachusetts General Hospital, in 1910. In its various phases, this research has continued to the present time in the laboratory and the clinic, the emotive experiences of the war adding an overwhelming amount of human data to laboratory findings. As stated in the preceding report, 1 it is practically impossible to formulate any experiment so that but one stimulus will act upon