VELOCITY AND PRESSURE OF BLOOD-FLOW. 



505 



the closed area are recorded through the tambour system connected 

 with the cuff. By means of a suitable stop-cock the pressure in 

 the cuff is dropped, 5 mms. at a time, and a record of the pulse is 



Fig 202. Rec9rd (Erlanger) to show the maximum size of the recorded pulse 

 wave when the outside or extravascular 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*s 



taken at each level. The point of systolic pressure is indicated 

 either by a sudden increase in the size of the pulse or by a sudden 

 spreading of the limbs of the pulse wave. As the pressure is 



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 

 k> the delicate tambour, h, and are thus recorded. 



dropped in steps below this point the size of the pulse wave in- 

 creases to a maximum, and then again declines (Fig. 202). The 

 pressure at which the maximum pulse waves are obtained or (Er- 

 langer) the first decrease in the size of the waves indicates diastolic 



