Further evidence of the reliability of the flicker method of studying temp. sensation was outlined. Two types of spatial summation for warmth were found. One occurred peripherally, probably between branches of a single fiber; the other occurred centrally, between different fibers. The 2d type of summation was not the result of a lowered synaptic resistance. One fiber and its branches served about 3-5 sq. cm. of the forehead. Areal discrimination of warmth was relatively poor at areas less than about 3 sq. cm. and was a rapidly changing function of area. For areas larger than 3 sq. cm., the relative discrimination was better and was practically constant. A general expression for sensory response in terms of the threshold sensation was obtained for the forehead for areas larger than 3 sq. cm. and intensities below 1,000 units. Super-liminal sensations obeyed the same law as the threshold sensation.