A satisfactory apparatus for study of analgesia in mice.

The white mouse is a suitable animal for the study of the threshold to induced pain because if dropped upon a heated surface it will sharply withdraw its paws when the sensation of heat is succeeded by pain, the time lapse before this withdrawal being quite constant in individual animals. The only difficulty in our experience has been to obtain a constant and uniformly heated surface upon which to drop the mouse, a handicap now overcome through the development of the herein described apparatus, which is a modification of an arrangement discussed with one of us (H. B.) by N. B. Eddy, of the National Institutes of Health, who based his method upon that described by Woolfe and MacDonald (1). The apparatus, shown in Fig. 1, consists of a copper teakettle, the large opening of which is sealed with a copper plate and the spout of which is con-