502 



CIRCULATION OF BLOOD AND LYMPH. 



and at a certain point disappears entirely. The pressure, as re- 

 corded by the manometer, at which the arterial sound disap- 

 pears marks the diastolic pressure, approximately at least. Ac- 



Fig. 202. Record (Erlanger) to show the maximum size of the recorded pulse 

 wave when the outside or extra vascular pressure is equal to the internal diastolic pressure 

 Ine artery is compressed first with a pressure above systolic, sufficient to obliterate the 

 lumen. As this pressure is lowered in steps of 5 mms. the recorded pulse wave increases in 

 size to a maximum and then again becomes smaller. The outside pressure with which the 

 maximum pulse is obtained measures the amount of the internal diastolic pressure (Marey'a 



cording to some observers, the diastolic pressure is indicated 

 more accurately by a change in the character of the sound, from 

 sharp to dull, which takes place just before it disappears.* If, 



Fig. 203. Schema showing the construction of the Erlanger apparatus: a, Rubber 

 bag of the arm piece ; c, bulb for blowing up this bag and putting pressure on the arm ; 6, 

 the manometer for measuring the pressure ; i, two-way stopcock (when turned so as to 

 communicate with the capillary opening, k, it allows the pressure in a to fall slowly); e, 

 a rubber bag in a glass chamber,/; e communicates with a when stopcock d is open and 

 the pulse waves from a are transmitted to e; the pulsations of e in turn are transmitted 

 to the delicate tambour, h, and are thus recorded. 



however, for any reason it is desirable to obtain a record of the 

 systolic and diastolic pressures, some form of sphygmomanometer 



* Taussig and Cook, "The Archives of Internal Medicine," 11, 542, 1913; 

 also Hooker and Southworth, ibid., 13, 384, 1914. 



