1. Medium and large doses of digitalis applied in Ringer solution have after a short while a systolic effect, minimal effective doses after a long time, a diastolic effect.
2. Raising the calcium concentration after large doses of digitalis increases, after small doses decreases the systolic action.
3. The immediate action of increased calcium content of the Ringer solution on the normal heart consists in an increase of the systolic contraction, the prolonged action in a decrease.
4. Systolic or diastolic standstill of the heart as produced by digitalis cannot be produced by the application of high calcium concentration on the normal heart.
5. The mode of the interaction of digitalis and calcium is discussed.