ABSTRACT
When the crop of Aplysia is bathed by a solution containing 0.011 M KC1, tonic contraction and inhibition of the rhythmic movements result if potassium is either withdrawn or added in excess.
The action of potassium on tone in the Aplysia crop is independent of the calcium concentration.
Rb, Cs and NH4 act like potassium on the Aplysia crop, but Li does not. Rb is about twice as active, Cs about one-half as active, and NH4 about one-fifth as active as potassium.
The changes of tone seen in the Helix crop when the potassium concentration is varied are identical with those seen in vertebrate plain muscle under like conditions.
Addition of a little potassium to the heart of Maia perfused with a potassium-free fluid causes a drop of tone. High concentrations of potassium have two opposed effects, a contracting action and a secondary depressing action.
The action of potassium on the striped muscle of the Maia heart is essentially like its action on molluscan or vertebrate plain muscle.
A valuable review of the different kinds of muscle-fibre found in gasteropods has been published by Plenk (1924)
For a full account of the behaviour of the preparation in sea-water see Bottazzi (1898).
This effect is more clearly seen in the adductor muscle of the claw, which is contracted by isotonic NaCl or CaCl2, but relaxes in NaCl 100 c.c. +CaCl2 4 c.c. The NaCl contraction is accompanied by spontaneous twitches and is rapidly reversible ; the CaCl2 contraction is smooth and only slowly reversible.
