230 



PHYSIOLOGICAL PHYSICS. [Chap. xxi. 



By the cardiograph (Fig. 107) Marey has ap- 

 plied the same method to obtain tracings of the 



movement of the heart from the 

 outside. The tambour is fitted in 

 a vulcanite box c. On the disc 

 in the centre of the membrane a 

 is fixed a vulcanite knob 6, which 

 is applied to the spot on the chest 

 where the shock of the heart is 

 felt. By means of the spiral 



Fig. 107. Cardiograph J , 7 , 



of Marey (in section), spring and screw a the sensi- 

 bility of the instrument can be 

 increased or diminished. The variations of pressure 

 produced by the movements of the heart are conveyed 

 by an iiidiarubber tube efto a registering instrument 

 in the usual manner. 



The speed of the Moocl stream has been deter- 

 mined by various forms of ap- 

 paratus. First in point of time is 

 that of Yolkmann (1850), which is 

 called the haeinodromoiiBeter. 

 It consists of a bent U-tube with 

 limbs of equal length 2, 3 (Fig. 108), 

 between which a scale is fixed. 

 These are fixed in a basement piece 

 5, 6, fitted with cocks 1, 4, and sup- 

 plied at each end with a caiiule 

 7 8. The cocks of the basement 

 piece communicate with one 

 another, and have a passage bored 

 straight through and a passage at 

 right angles to it opposite each limb 

 of the U-tube. By a simple 

 mechanical contrivance the cocks can be turned so 

 that the through passage only is open, or the cross 

 passages only. By this means, in the first case, fluid 

 would pass straight through without entering the 



108. Volkmann's 

 Hamiodromometer. 



