ABSTRACT
The heart of Palinurus lalandii and the ventricle of Octopus horridus maintain their normal rhythm for long periods in solutions containing only sodium and calcium chlorides.
The removal of calcium from the perfusion fluids causes systolic arrest in both hearts.
Both hearts are sensitive to very low concentration of potassium when perfused with potassium-free fluid.
Excess of magnesium and strontium produce the same effect as excess of calcium, but magnesium cannot be successfully substituted for calcium in the perfusing fluid.
The physiological range of H ion concentration is determined for the two preparations.
Both hearts have low temperature optima, and the high limit of their range is in the neighbourhood of 20° C.
Recent experiments have shown that this sensitivity to potassium only develops in hearts that have been perfused for a short time with potassium free medium. When potassium is included in the medium from the beginning of perfusion the heart will beat normally in Na 100 : Ca 5 : K I, and will tolerate a triple increase of potassium without injurious effects. The complete removal of potassium, however, invariably brings about a marked improvement in tone, frequency and regularity of beat.
In a private communication from Prof. Hogben we learn that in some unpublished experiments carried out at Plymouth on Portunus and Cancer he obtained an analogous sensitivity to the inhibitory action of potassium.
