The juice of Cavernularia filtered through filter paper does not re spond to the strongest interrupted induced shocks. The living colony, however, responds readily.
When a galvanic current is passed through one of the excised polyps mounted between non-polarizable electrodes, a flash of light occurs on the make and a series of flashes while the current is passing, which cease on the break. There is no flash of light on the break. A similar response can be observed with Noctiluca (2). It will be remembered that Romans (es) observed a series of contractions in the bell of a medusa during the passage of a galvanic current, and the sartorius muscle of the frog often contracts on the make of a galvanic current, remains contracted during the passage of the current, and relaxes on the break.
If the whole colony be stimulated by weak induced shocks, there is a local production of light. There is usually no response to a single shock, but a ready response to three or more sent in in rapid succession.
With stronger stimuli, a wave of light, easily followed by the eye, passes over the colony in each direction from the point stimulated.
With interrupted induced shocks, a series of waves of light follow one another in quick succession (not corresponding to the number of stimuli, however), reminding one of the series of electric shocks given out by the torpedo, only on a slower scale. The time-interval between separate flashes no doubt corresponds to the refractory period of the cells concerned.
On pressing deeply into the tissue and stimulating strongly, a much brighter light-response also results, which very slowly moves away from the point of stimulation and usually does not extend more than 2 or 3 cm. At the same time the whole colony contracts, the polyps are drawn in, and in this condition do not respond to electrical stimu lation by light-production.
The wave of light above mentioned will pass in any direction over the colony and across a cut around the middle of the colony involving the whole of the external tissue. Some inner tissue must therefore be capable of conducting the stimulus.