Observation was performed on 23 subjects with marked propagated sensation along meridians(PSM)and 30 without PSM.The electroretinogram(ERG)was recorded with surface electrode and added by an averager.The b wave of ERG evoked by flash stimulation was positive with a latent period about 60 ms and amplitude of 22±1.66μv(n=53).There were 2 types of ERG response during puncturing Hegu(LI 4).The amplitude of ERG b wave increased in 33 subje- cts and decreased in 20 subjects.However

the acupuncture effect was kept rela- tively stable in each subject.The spontaneous variation of ERG amplitude was about 10%.In contrast

it changed by 26.5±2.43%(n=20)when Hegu(LI 4)was acupunctured alone.It is particularly to be noted that the amplitude of b wave almost remained unchanged

with in the range of 10.08±2.42%(n=20)

as the pressure was applied on Shousanli(LI 10)during acu puncture

no matter whether the subjects with or without PSM.However

the variation rate of b wave increased by 24.83±3.74%(n=15)once again

if the pressure was applied on both side of Shousanli(LI 10)

it was nearly equal to the value caused by acupuncture Hegu(LI 4)alone.The contrast between the two is striking.The result revealed again that there may be a certain substantial process advancing along the channel during acupuncture.It is the blokade of this process by me chanical pressure which leads to the decrease of the acupuncture effect.