vni BLOOD-STREAM : MOVEMENT IN VESSELS 247 



Marey's sphygraonianometric method consists in applying a 

 variable external counter-pressure not to a limited point of an 

 artery, but to the whole surface of a limb. He introduced the 

 forearm into a cylindrical vessel closed by a rubber ring, which 

 was filled under easily adjustable pressure with water, and 

 connected with a recording manometer, and then took a tracing 

 of the total pulsations of all the arteries of the forearm. He saw 

 that with gradual increase of hydrostatic pressure within the 

 cylinder, the pulsations increased during a first period, and then 

 diminished in a second, till they ceased entirely. In the tracings 

 of Fig. 94 it can be seen that the pulsations attain 

 their maximal excursion when the counter-pressure 

 on the forearm reaches 8 cm. Hg ; they then gradu- 

 ally diminish, and almost entirely disappear at a 

 counter-pressure of-19'5 cm. Hg. 



In a second series of experiments Marey, in order 

 to make his method more practicable, gave up the 

 pressure on the whole forearm, and confined himself 

 to one finger of the hand, as seen in the apparatus 

 of Fig. 95. In order to make the pulsations of the 



FIG. 95. Marey's sphygmomanometer. It consists of a glass holder M, which is completely closed 

 after introducing the fore-finger, and communicates on the one hand with a capillary mercury 

 manometer 6, on the other with a stout bag c, which is gradually compressed by a screw. The 

 whole apparatus should be filled with water, care being taken to avoid air-bubbles. 



digital arteries more conspicuous, he employed a mercury mano- 

 meter of ^ mm. diameter, and limited himself to reading the 

 maximal and minimal values of the pulsatory oscillations on the 

 scale. This method again confirmed the preceding observation, to 

 the effect that the pulsations, with increase of counter -pressure, 

 are greater at first, and subsequently diminish and tend to die out. 

 But he also found that it was very difficult to obliterate them 

 completely, even when the counter-pressure reached a height of 

 28-30 cm. Hg, i.e. a value which is certainly higher than the 

 pressure exerted by the blood on the arteries of the fingers. 

 According to Marey, however, the value of his method lies in the 

 determination of the counter-pressure with which the most "ample 

 oscillations of the mercury column are obtained. "At that moment," 



