VELOCITY AND PRESSURE OF BLOOD-FLOW. 



501 



ments are made upon the brachial artery at the level of the heart, 

 and consequently no correction need be made for a hydrostatic 



Fig. 204.- 



-Erlanger apparatus. The collar for the arm i.s not shown, 

 understood by reference to the schema given in Fig. S 



The parts may be 



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, h, 

 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 

 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 systoHc 

 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- 



