Fig. 61.—Muscle in tube of oxygen over mercury. "a", platinum wire fused into end of tube and connected with small hook, from which a frog's limb is suspended; "c", toe of limb ; "b", trough containing mercury. A small amount of mercury is on the side of the tube between mercury in "b" and toe at "c", so that induction shocks sent in by "x" and "y" readily tetanise the limb. The limb receives tetanising shocks at intervals of thirty seconds, and the experiment may go on for sixty or eighty minutes.