If non-polarisable electrodes are placed upon the body of the toad, the one contact lying on the muscle near the root of the neck in front and on the right side, while the other contact rests on the muscle in the centre of the abdominal wall, and these contacts are united to the string galvanometer in such a way that relative negativity of the cephalic contact yields in our photograph an upward excursion ; then the form of the curve which is written at each cycle of the heart may be exemplified by the upper curve of fig. 1 (next page). This curve is representative, and is a record of events which are almost uniform when the heart is beating normally and its rate is about 25 beats to the minute. It consists of an upward, rounded, and sometimes subdivided deflection, P ; this deflection is followed by a period of rest, during which the string lies on the zero line or near it. Ventricular activity is first signalled by the summit R , and this elevation invariably begins in a gradual fashion, its steepness increasing as it proceeds. The string, after a variable interval of from 0∙0400 to 0∙0900 second, falls back towards the base line. It may or may not attain that line, but it usually does, and, travelling somewhat beyond, produces a diminutive deflection S ; this ends the first part of the ventricular complex. Then follows a second period of rest, which is finally disturbed by a slow and upward movement of the string in the inscription of the deflection T . In many cases a notch, B , is found in the interval between S and T . (The little deflection B has usually a downward direction, and is the result of activity in the truncus arteriosus .)