246 PHYSIOLOGY CHAP. 



a metal manometer, the indicator of which shows the pressure 

 exercised on the artery. When the indicator no longer shows 

 pulse -waves in the compressed artery, the internal pressure, 

 according to v. Basch, must (at any rate approximately) be equal 

 to the external compression. Tigerstedt rightly pointed out the 

 untrustworthy character of the values obtained by this method. 

 In spite of the improvements introduced by Eabinowitz (1881) 

 and Potain (1889) in the apparatus, and adopted by von Basch in 

 the latest model of his sphygmornanoineter (1890), and notwith- 

 standing the many control experiments carried out by various 



FIG. 94. Tracings of pulsatory oscillations in volume of forearm, recorded with Marey's 

 sphygmoinanometer. Shows the variations under the influence of increasing external 

 pressure, as indicated in cm. Hg at the side of each tracing. (Marey.) 



authors upon animals (which show that while the pressure values 

 obtained from this instrument are unreliable, they still yield 

 results comparable inter se on the same individual), there are 

 certain obvious drawbacks to its practical application to man 

 which are not easily removed, and which render it untrustworthy. 

 The results may vary considerably in different cases, according to 

 the depth of the paniculus adiposus, the development of the 

 muscles, the arrangement and normal or sclerotic state of the 

 arterial walls, and in particular the tension of the aponeurotic 

 fascia which cover the arteries investigated, and more or less hinder 

 their compression. 



The investigations initiated by Marey (1876), resumed in 1878, 

 and continued in Italy in 1895 by Mosso, were more successful. 



