[Distinction of fast fibers and slow fibers in frog abdominal muscle using certain choline esters]

We have registered the contractions of the frog's abdominal muscle in Ringer's solution. The contractions were produced either by acetylcholin or by succinyldicholin. The graphics showed that the succinyldicholin contractions were much slower than the acetylcholin ones. The tracings were not equalized by a preliminary addition of eserin. We conclude that acetylcholine excites the fast fibers and that succinyldicholin excites the slow fibers of the muscle.