Since the first description of the auscultatory blood pressure sounds by Korotkov in 1905, this method has been more and more employed until today it is the standard, recognized method of determining the points in the blood pressure reading. When one applies the 12 cm. arm band over the brachial artery and listens with the bell of the stethoscope about one cm. below the cuff directly over the brachial artery near the bend of the elbow, one hears an interesting series of sounds when the air in the cuff is gradually reduced. The cuff is blown up above the maximum pressure. As the air pressure around the arm gradually is lowered, the series of sounds begins with a rather low-pitched, clear, clicking sound. This is the first phase. This only lasts through a few millimeters fall when a murmur is added and the tone becomes louder. This click and murmur phase is the second phase. A few millimeters more of drop in pressure and a clear, sharp, loud tone is audible. Usually this tone lasts through a greater drop than any of the other tones. This is the third phase. Rather suddenly the loud, clear tone gives place to a dull muffled tone. In general the transition is quite sharp and distinct. This is the fourth phase. The tone gradually or quickly ceases until no tone is heard. This is the fifth phase (Ettinger.) The first phase is due to the sudden expansion of the collapsed portion of the artery below the cuff and to the rapidity of the blood flow. This causes the first sharp clicking sound which measures the systolic pressure. The second, or murmur and sound phase, is due to the whorls in the blood stream as the pressure is further released and the part of the artery below the cuff begins to fill with blood. The third tone phase is due to the greater expansion of the artery and to the lowered velocity in the artery. A loud tone may be produced by a stiff artery and a slow stream or by an elastic artery and a rapid stream. This tone is clear cut and in general is louder than the first phase. The fourth phase is a transition from the third and becomes duller in sound as the artery approaches the normal size. The fifth phase, no sound phase, occurs when the pressure in the cuff exerts no compression on the artery and the vessel is full throughout its length. It is generally conceded that the sounds heard are produced in the artery itself and not at the heart. The tones vary greatly in different hearts. A very strong third tone phase or prolongation of this phase usually means that the heart which produces the tone is a strongly acting one, although allowances must be made for a sclerosed artery in which there is a tendency to the production of a sharp third phase.