The cuff was made 12 cm. in diameter because it was shown (v. Recklinghausen) that with narrow cuffs much pressure was dissipated in squeezing the tissues. Janeway has shown that with the use of the 12 cm. cuff accurate values are obtained independently of the amount of muscle and fat around the brachial artery. In other words if an actual systolic blood pressure of 140 mm. is present in two individuals, the one with a thin arm, the other with a thick arm, the instrument will record these pressures the same where a 12 cm. arm band is used. We need have no fear of obtaining too high a reading when we are taking pressure in a stout or very muscular individual. Janeway also was the first to call attention to the fact that the diastolic or minimal pressure was at the point where the greatest oscillation of the mercury took place. This is difficult to estimate in many cases as the eye can not follow slight changes in the oscillation when the pressure in the cuff is gradually reduced. Practically this is the case in small pulses. The Riva-Rocci instrument was modified by Cook. (See Fig. 13.) He used a glass bulb containing mercury into which a glass tube projected. The bulb was connected by outlet and tubing to the cuff and syringe. The glass tube was marked off in centimeters and millimeters and for convenience was jointed half way in its length. The instrument could be carried in a box of convenient size. This instrument is fragile and more cumbersome, although lighter in weight, than others and is very little used at present. [Illustration: Fig. 13.--Cook's modification of Riva-Rocci's blood pressure instrument.] Stanton's instrument (Fig. 14) is practically Cook's made more rigid in every way but without the jointed tube. The cuff has a leather casing, the pressure bulb is of heavy rubber, the glass tube in which the mercury rises is fixed against a piece of flat metal and there are stopcocks in a metal chamber introduced between the bulb and mercury with which to regulate the in- and out-flow of air. The pressure can be gradually lowered conveniently without removing the pressure bulb. [Illustration: Fig. 14.--Stanton's sphygmomanometer.]