It has been found that a blow to the sagittal crest of the fixed head of the intact dog generally will produce an experimental concussion twice as severe as an equivalent blow to the free head. In preliminary experiments the dog has been found to be much more susceptible to concussion from a blow to the external occipital protuberance than any other location, and the effect appears to be equally severe in either fixed or free head condition.

The physiological response of the macaca speciosa (stump tail) monkey in the 15 to 20 lb range has been found to be different and much less sensitive than that of the dog or cat. The authors believe that to relate experimental concussion results to man more investigation is necessary on the anesthetized and relatively conscious primate.