ABSTRACT
Some years ago, the writer published an account of the action of potassium on the crops of Aplysia and Helix, and the hearts of Maia and Homarus (Wells, 1928). It was pointed out that the preparations used show a general resemblance in their responses to changes in potassium concentration, although they include plain and striped muscle, and are taken from molluscs and crustaceans. Since that time he has made similar experiments on other preparations. The results are now described and discussed from a comparative standpoint. It appears that potassium—in contrast to calcium, which has the most diverse effects—-produces essentially similar responses in muscles from animals of various different phyla, and of quite different histological and functional nature. The suggestion is made that all types of rhythmic muscle are essentially alike in their responses to comparable changes in the potassium concentration of the environment.
It is assumed throughout this paper that the divalent ion concentrations are kept constant. The fore-gut of Dytitcus remains active at very high potassium concentrations if the calcium is also greatly increased (Hobson, 1928).
