“_Method by Auscultation._--This is by far the most accurate method of determining the blood-pressure, and the results obtained in this way should be free from error, or the dangers of personal equation in palpating the artery at the wrist. “_Systolic or Maximal Pressure._--Bare the arm and adjust the sleeve well up; place the stethoscope over the brachial artery about 1 cm. below the border of the cuff, then constrict the arm by inflating the bag until no sound is heard in the artery through the stethoscope. At this point release the air slowly by means of the escapement valve, and soon a clear, clicking sound will be heard, which indicates the first passage of the blood stream below the constricting arm band and is the true systolic or maximal pressure. “_Diastolic or Minimal Pressure._--Still gradually releasing the air, this clear, clicking tone (first phase) is followed by a low tone or murmur (second phase), and this murmur is followed by a loud, clear tone (third phase), this in turn by a perceptibly dull tone (fourth phase), and this dull tone represents the diastolic or minimal pressure. “Below are given the five different phases of tone to be heard in the auscultatory blood-pressure phenomena as found by Louis M. Warfield, A.B., M.D., and confirmed by his clinical observations on animals. “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.” He also says that blood pressure always depends on four factors, viz.: 1. Cardiac energy. 2. Peripheral resistance. 3. Elasticity of the arterial walls. 4. The amount of blood in circulation.