1966 Volume 7 Issue 2 Pages 1-7
1) When a heating source was approached in front of Trimeresurus flavoviridis whose eyes were covered for the absence of vision, the snake sensitively responded to the radiation. The first reaction of response was tongue flickering and rotation of head to chase the movement of a radiant body and afterwards the snake stroke it. The threshold of the radiation to evoke the snake's first reaction was measured and both sides of the facial pits were plugged using putty and polyvinyl tape. The sensitivity to the radiation was remarkably reduced in this state and became recovered when the plugs were removed. It was proved that the snake could find and strike the warm-blooded pray in the darkness at night and this sensory organ was the facial pits.
2) The radiant body used in this experiment was mostly a small electric heater of which radiant energy was variable in the range under 0.7 cal/sec. The others partially used were a candle with the energy 11.5 cal/sec, a man's hand and a rat, Rattus rattus weighing 80 g whose radiant energy was estimated as 0.222 and 0.083 cal/sec respectively calculated from their basal metabolisms.
3) In the absence of vision, the end-point of sensible radiation from an electric heater was presented as 0.34-3.37 × 10-4 cal/cm2/sec with an average 1.22 × 10-4 cal/cm2/sec among 9 snakes. In the snakes of the plugged pits, no response was observed in the radiation 11.86-21.7 × 10-4 cal/cm2/sec and the end-point of the sensibility was 22.4-58.5 × 10-4 cal/cm2/sec with an average 36.6 × 10-4 cal/cm2/sec. After the plugs were removed the sensitivity was recovered to 0. 32-2. 04 10-4 cal/cm2/sec with an average 0.71 × 10-4 cal/cm2/sec. In the last state, the threshold was one tenth less when a hand or a rat were applied as a radiant source as presenting 0.11 and 0.09 × 10-4 cal/cm2/sec respectively. The radiation from living things was differed from that of the electric heater in irradiating from a certain spread of areas and in having longer wave length of infrared radiation.
4) In a blindholded snake whose end-point of radiant response was first 0.68 × 10-4 cal/cm2/sec and little difference presented in the sensitivity, when one side of facial pits was plugged. The latter value was 0.45 × 10-4 cal/cm2/sec. The median limit of the sensitive field of a pit organ extended not acrossing the sagittal line, 7.4° lateral to the same side and the external limit was 114.30 from the sagittal line in average of 3 specimens. Orientation of striking was still correctly held when one side of pits was plugged.