Abstract
1. The relations between the length and the resting tension, contraction tension, potentiated tension and the tension of spontaneous contraction were determined in guinea-pig's taenia coli.
2. The resting tension was measured during relaxation induced by 10-7g/ml adrenaline, and the active tension was measured during contraction developed by optimum a. c. field stimulation.
3. The slightest resting tension was produced at 75% of the in situ length. The elastic modulus was 0.007 kg/mm2 and it was markedly decreased in the procainized preparation.
4. The in situ length was 90% or less of the optimum length, at which the active tension was maximum.
5. The maximum tension potentiated by successive stimuli was attained at 75% of the in situ length.
6. On stretching, the number of muscle cells participating in spontaneous contraction increased.
7. On stretching, the time of spontaneous contraction increased and that of relaxation decreased. Consequently the period of spontaneous contraction did not change at lengths less than 125% of the in situ length, but contraction pattern changed at lengths more than 125% length.
