THE FLOW OF BLOOD IN THE ARTERIES 



203 



e.g., the radial), and pressure is applied until no pulse can be felt by the finger 

 placed peripherally to the instrument. The pressure which the manometer now 

 shows is the desired value. This instrument appears to be incapable of giving 

 an absolute value of sufficient accuracy, although it has proved admirably fitted 



FIG. 76. Erlanger's apparatus for determination of the blood pressure in man. The appa- 

 ratus is provided with a pneumatic cuff, C, which consists of an inside rubber bag and an 

 outside leather band. The whole cuff can be buckled around the arm above the elbow. 

 The air cavity within the rubber bag of the cuff communicates through a thick-walled 

 rubber tube and a four-way connection, 2 =f^= with the three other essential parts of the 

 apparatus, namely: (1) downward, with the valved bulb, V B, by means of which air can be 

 forced into the cuff and can thus be made to compress the arm ; (2) to the left, with the mer- 

 cury manometer, M, from which the amount of pressure applied to the arm can be read 

 directly in mm of Hy; and (3) upward, with the distensible bag, B, inside the glass cham- 

 ber, G. This bag, last mentioned, responds to fluctuations of pressure inside the rubber bag 

 of the arm, which are due to vibrations of the arterial wall, and the tambour at the top 

 records such vibrations on the drum, D. 



for the determination of variations in pressure in the same person, provided 

 neither too little nor too much time is covered by such variations. 



Other authors compress a section of a whole limb by means of a suitably 

 constructed pneumatic cuff, and measure the pressure inside the cuff at which 

 the pulse in some distal artery disappears or reappears. As H. v. Reckling- 

 hausen has shown, one must choose for this purpose a cuff of considerable breadth, 

 for otherwise a portion of the pressure is consumed by the neighboring soft parts 

 and one obtains too high a value. The broader the cuff, the more is this disad- 



