Abstract
On the sartorius muscle of Buf o vulgaris, dual stimuli of subthreshold strength were applied through Pratts pore-electrod or through the separating box devised by Sugi and the local excitation of muscle fiber evoked by the subthreshold stimulus was examined. Two contact keys of the pendulum of Azuma's type were used to produce the double electric pulses of short dura-tionwith short interval.
The duration of first puls was 55 usec and the second 60 μsec. The hight of local exita-tion coused by the first conditioned puls of subthreshold was tested by controlling the intensity of second puls. The minimal contraction of the muscle was used as the indicator of the effect of second puls. It became clear that the duration of the local excitation were ca 7 msec.
It developed promptly to its maximal strength in 1 msec and decayed to the nomal level after 1 msec, and then followed a reversed change (lowering of the excittability) for 3 msec. The change of the excitability caused by the subthreshold stimulus in the muscle showed in this way a quasi vibration.
Maximal height of the elevated excitability was proportional to the strength of the conditioned stimuli and the time constants of the decay were found to show similar values when the stimuli were weaker than 30-40% of the normal threshold.
Conditioned Stimuli stronger than 40% of the threshold caused to elongate the time nescessary for the descending of to the half value of the maximal height (half-time) . Half-time became longer and longer according to the strengthening of the conditioned stimuli, but the total duration of the appearance of local excitation was held strictly constant.
The local excitation was elevated under the influence of negative electrotonus and lowered by positive electrotonus. DFP and Eserine acts to lower the local excitability. Effect of the Acetylcholine upon the local excitation was not remarkable.
