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to the arm with a special clamp. The inflating apparatus is a double bulb such as is employed with a thermocautery.
Advantages.—The apparatus stands firmly on a solid base has a scale easily read, it is adjusted rapidly and is rapid in operation.
Disadvantages.—The armlet is too narrow for accurate readings, the apparatus is too fragile and totally unavailable for pressures over 260 mm. (10 in.) of mercury.
Fig. 10.—Riva-Rocci's sphygmomanometer. (Sahli and Potter.)
2. Cook's Modification of the Riva-Rocci (Fig. 11).-This is very similar to the preceding but is of lighter construction, and is provided with a jointed manometer tube which allows the instrument to be packed in a smaller space. It employs the double bulb inflator, and gives readings directly in millimeters Hg. which are read from a scale etched upon the glass.
Disadvantages.—It does not stand firmly being easily upset and broken. Without special care in packing and transportation the mercury is frequently spilled. The caliber of the tube (1 mm.) is too small. The scale etched upon the glass is difficult to read.
3. Stanton's (Later Called Sands) Sphygmomanometer (Fig. 12).—This instrument was devised in an effort to increase portability, to reduce the probability of breakage
Fig. 11.-Cook's modification of the Riva-Rocci sphygmomanometer,
showing narrow arm-band in place, with cautery bulb inflator.
and to lessen the elasticity of the tubular system, thereby improving the diastolic fluctuation of the mercury.
These changes were effected by substituting a metal cistern and by arranging over this a screw joint for the attachment of the vertical glass tube; also by the introduction of a stopcock in the short tube as it emerges from the cistern to serve for attachment of the inflating bulb. This eliminates the elasticity of the inflating apparatus during the diastolic reading. The instrument employs the standard 12-cm. (442-in.) cuff, retained on the arm by a canvas outer cuff and buckle straps.
Disadvantages.—Chiefly the time and skill required to set up the apparatus before using, and the great difficulty
Fig. 12.-Stanton's sphygmomanometer, showing arrangement of parts
with cautery bulb inflator.
in avoiding the loss of mercury during the setting-up process. Also the cistern arrangement gives low readings in high pressures.
4. Janeway's Sphygmomanometer (Fig. 13).—In the construction of the Janeway apparatus we see a return to the U-tube type, first devised by von Basch. This form appears to be a more accurate method of employing the mercury column, as in the cistern form no cognizance is taken of the change in the level of the mercury in the cistern, which must, for physical reasons, give too low readings when employed in the study of high pressures.
This instrument employs the circular compression band of standard width and a Politzer bag for inflation. In
addition to this the only original feature of this instrument is the jointed U-tube which allows the instrument, with the exception of the cuff and inflating bag, to be contained in a case measuring 1044 X 458 X 178 in. and weighing 212 lb. The open end of the manometer tube is closed with a cork when not in use, and the rubber connection on the other limb leading to the attachments is compressed by closing the case, to prevent loss of mercury from the manometer. The scale is arranged to slide down into the box when not in use. The arm-band is 12 cm. (442 in.) wide and is retained on the arm by a non-elastic outer cuff provided with friction straps.
Advantages. This apparatus is light, compact and portable and the readings accurate.
Disadvantages.—The frailness of jointed U-tube. The mercury is easily spilled because of the inadequate method employed to confine it when the instrument is not in use. The rubber connections are short-lived and must often be renewed.
5. The Faught Standard Mercury Sphygmomanometer (See Fig. 14).—This apparatus was devised early in 1909, in an endeavor to overcome the shortcomings of existing