ANNOTATION The Efect of Potassium and Calcium on The Electrocardiogram

The force and general behaviour of cardiac con-traction can be altered in striking fashion under experimental conditions by varying the physical and chemical composition of the fluid bathing the heart muscle. Slight increases in alkalinity or acidity bring about a lengthening or shortening of systole respectively and influence the transmission of the impulse in the conduction system. The ionic content of extracellular fluid, its historical deriva-tion from its primitive forerunner sea water, and the importance of changes in its composition to the economy of the individual have been portrayed lucidly by Gamble (I942). The three cations potassium, calcium and sodium must be present in fairly inflexible con