504 CIRCULATION OF BLOOD AND LYMPH. 



ered again the pulse reappears. Among other sources of error involved in 

 this method it is to be remembered that trie tactile sensibility is not sufficiently 

 delicate to detect a minimal pulse in the artery. Other methods of determin- 

 ing the systolic pressure (see below) indicate, as a matter of fact, that the 

 pulse continues some time after an individual of average tactile sensibility is 

 unable to detect it. 



For practical purposes, a great improvement was made by 

 Korotkoff in the introduction of the auscultation method by means 

 of which both systolic and diastolic pressures may be determined 

 rapidly with approximate accuracy. In this method the cuff 

 with its pneumatic bag (a) is placed round the arm above the elbow, 

 and by means of a bulb (c) or pump the pressure within the pneu- 

 matic bag is raised until the brachial artery is completely obliter- 

 ated. A stethoscope is now applied to the location of the brachial 

 artery just below the lower edge of the cuff, and by means of a 

 needle valve the pressure on the artery is allowed to drop slowly. 

 The moment that the pressure falls to a point at which a pulse 

 wave can break through the constricted area a distinct sound 

 will be heard in the stethoscope. If the mercury manometer is 

 read at this point, it will give the value for the systolic pressure. 

 As the outside pressure continues to fall the sound alters in char- 

 acter. According to the description of Ettinger* it passes through 

 five phases: 1, The initial sharp clear sound; 2, muffled with the 

 character of a murmur; 3, clear and loud; 4, dull; 5, cessation. 

 Some observers have thought that the fifth phase, the cessation of 

 the sound, marks the point of minimal or diastolic pressure, but 

 later workers seem to agree that this pressure is indicated more 

 accurately by the transition from phase 3 to phase 4, at the begin- 

 ning of phase 4. The difference in pressure between this point 

 and that at which the sound disappears may be slight ordinarily, 

 but in some cases may be considerable.! If, however, for any 

 reason it is desirable to obtain a record of the systolic and dias- 

 tolic pressures, some form of sphygmomanometer must be employed 

 in which the pulse from the artery under the cuff is recorded upon 

 the smoked surface of a kymographion. Several instruments of 

 this kind have been described, but the one devised by ErlangerJ 

 is probably the most complete. This instrument is illustrated in 

 Figs. 203 and 204, and is described in some detail below. When 

 the pressure in the cuff is raised above the systolic level the brachial 

 artery is completely closed, but the pulsations of the stump above 



* Ettinger, "Weiner Klin. Wochenschrift," 20, 992, 1907. 



t Weysse and Lutz, "American Journal of Physiology," 32, 427, 1913; and 

 Melvin and Murray, "Quarterly Journal of Experimental Physiology," 8, 125, 

 1914. 



t" American Journal of Physiology," "Proceedings of the American 

 Physiological Society," 6, xxii., 1902; and "Johns Hopkins Hospital Reports," 

 12, 53, 1904. 



