VELOCITY AND PRESSURE OF BLOOD-FLOW. 



503 



must be employed in which the pulse from the artery under the 

 cuff is recorded upon the smoked surface of a kymographion. 

 Several instruments of this kind have been described, but the one 

 devised by Erlanger* is probably the most complete. This in- 

 strument is illustrated in Figs. 203 and 204, and is described in 

 some detail below. When the pressure in the cuff is raised above 



Fig. 204. Erlanger apparatus. The collar for the arm is not shown. The parts may be 

 understood by reference to the schema given in Fig. 203. 



the systolic level the brachial artery is completely closed, but the 

 pulsations of the stump above 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 taken at each level. The point 

 of systolic pressure is indicated either by a sudden increase in the 



* "American Journal of Physiology," "Proceedings of the American 

 Physiological Society," 6, xxii., 1902; and "Johns Hopkins Hospital Reports," 

 12, 53, 1904. 



