VELOCITY AND PRESSURE OF BLOOD-FLOW. 507 



factor, such as would be necessary, for example, if the determi- 

 nations were made on an artery in the leg in a person standing 

 erect. 



The way in which the Erlanger apparatus is used may be understood from 

 the schematic Fig. 203. a is the rubber bag, which is buckled upon the arm 

 by a leather strap. This bag communicates with the mercury manometer, b, 

 with a pressure bag, c, through the two-way stopcock, i, and through the 

 stopcock d with a rubber bag, e, contained in a glass chamber, .f. This glass 



Fig. 205. To show the method of detecting the systolic pressure upon the tracing given 

 by the Erlanger sphygmomanometer. The pressure upon the arm is raised above systolic 

 pressure and is then dropped 5 mm. at a time, a short record being taken after each drop. 

 Records are shown for 130, 125, 120, 115, and 110 mm. At 115 mm. it will be seen that 

 the limbs of the pulse-wave show the separation or spreading which indicates the first pulse- 

 wave to get through the occluded artery, and therefore the systolic pressure. 



chamber communicates above with a sensitive tambour, h, and by means of the 

 stopcock g can be placed in communication with the outside air. The systolic 

 pressure may be determined in two ways: By one method only the mercury 

 manometer is necessary, the instrument corresponding with the Riva-Rocci 

 apparatus described above. By means of the pressure bag, c, the bag, a, up 

 the arm is blown up until the pressure is above the systolic pressure and the 

 radial pulse below disappears. By turning stopcock i properly the system is 

 allowed to communicate with the air through a capillary opening, k. Conse- 

 quently the pressure upon the artery in the arm falls slowly, and by palpating 

 the radial artery one can determine the pressure, as measured by the mercury 

 manometer, at which the pulse just gets through. This pressure will measure 

 approximately the systolic pressure. The second method (method of v. 

 Recklinghausen) gives higher and doubtless more accurate results. In this 

 method the pressure is at first raised above systolic pressure with stopcocks 

 d and g open, a, e, and b are under the same pressure. If stopcock g is now 

 turned off, the pulsations in a are transmitted to e and through it to the 

 tambour, h, and the lever of the tambour writes these pulsations on a kymo- 

 graphion. It should be explained that pulsations are obtained even when 

 the pressure on the arm is much more than sufficient to completely obliterate 

 the brachial artery. The reason for this is that the pulsations of the central 

 stump of the closed artery will be communicated to bag a. When the pressure 

 is suprasystolic these pulsations are small. If now the pressure in the system 

 is diminished slowly by turning stopcock i so as to communicate with the 

 capillary opening, k, it will be found that at a certain point the pulsations 

 suddenly increase in height (Fig. 205) . This point marks the moment when 

 the pulse wave is first able to break through the brachial artery, and it gives, 

 therefore, the systolic pressure. In many cases this method of determining 



