vin BLOOD -STEEAM: MOVEMENT IN VESSELS 267 



of pressure within the artery investigated ; it is only proportional 

 to the magnitude of the 

 local oscillations of the 

 pulse, which (as we saw 

 on p. 248) are, ceteris 

 paribus, in inverse ratio 

 to the tension of the ar- 

 terial walls. As a matter 

 of fact, not only the prim- 

 ary, but also the secondary 

 dicrotic wave is lower 

 with greater, and higher 

 with reduced arterial 

 pressure. Not even this 

 fact, however, can be 



taken as a "eneral law '' IG - 107. Burdon-Sandei son's cardiograph, which can also 



be used as a sphygmograph for the carotid, and a 



of contraction or relaxa- 

 tion in the artery explored 



lias great influence upon 



the amplitude of the 



sphygmic undulations. 



In order to realise this, 



we have only to consider the marked changes that appear in 

 the form and magnitude of the sphygmo- 

 gram after inhalation of amyl nitrite, which 

 immediately produces depression of arterial 

 tone (Fig. 105). The beats of the heart 

 become more frequent, and yet the amplitude 

 of the primary as well as^of the dicrotic 

 wave increases. 



Far more interesting and instructive, from 

 the clinical point of view, is the comparison 

 of the sphygmogram with the simultaneously 

 recorded cardiogram, as also the comparison 

 of two or more sphygmograms simultaneously 

 recorded from different arteries. For this 

 purpose, however, the direct sphygmograph 



FIO. los.-Edgren's sphygmo- is not suitable, and others with air transmis- 

 K 11 receivlng^anibonr'at" sion must beresortecl to. These are essentially 

 tached to a semicircular identical with cardiographs, but are different 



spring intended to fit round /> . . , 1 i i p 



the neck. The pressure of in form, since they are intended for use on 



pneumograph (Zimmermann's type). The apparatus rests 

 on three ebonite feet, which can be adjusted by screws. 

 It is fixed by a band to the thorax or nerk, so that the 

 central button, which has a steel spring (the tension of 

 which can be altered by a screw), presses against the 

 spot at which the beat of the heart or carotid pulse is 

 most perceptible. The transmission by air of the move- 

 ments of the spring is effected through a receiving 

 tambour, the position of which in regard to the spring 

 can be regulated by a screw. 



the 





the several arteries. One of these trans- 

 piate applied to the neck, mission spliyqmociraplis is that of Marey 



which stretches the spring f J '. Vi - x " ^ 1 



more or less according to the (represented in Jbig. 106), tor the radial 

 artery. A simpler model is that of Edgren 

 Burdon- Sanderson's cardiograph (Fig. 107) 



position of the screw. 



for the same artery. 



