112 



A MANUAL OF PHYSIOLOGY 



FIG. 32. PITOT'S TUBES. 



Of these methods, 3 and 4 are alone suited for the study 

 of thevelocity -pulse, that is, the change of velocity occurring 



with every beat of the heart. 

 The curves obtained by 

 Chauveau'sdromograph show 

 a general agreement with 

 blood-pressure tracings taken 

 by a spring manometer, and 

 with records of the external 

 pulse obtained by a sphygmo- 

 graph. There is a primary in- 

 crease of velocity correspond- 

 ing with the ventricular systole, and a secondary increase 

 corresponding with the dicrotic wave (Fig. 37). Like all 



the other pulsatory phenomena, 

 the velocity-pulse disappears in 

 the capillaries, and is only 

 present under exceptional cir- 

 cumstances in the veins. 



Pick, from a comparison of 

 sphygmographic and plethys- 

 mographic tracings (p. 116), 

 taken simultaneously from the 

 radial artery and the hand, has 

 demonstrated that in man the 

 velocity-pulse exhibits the same 

 general characters as in animals 

 (Figs. 34 and 35). And v. Kries 

 has confirmed Fick's conclu- 

 sions by actual records of the 

 velocity-pulse obtained by means 

 of an arrangement called a gas 

 tachograph (Fig. 38). 



This consists of a plethysmo- 

 graph connected with the tube 

 of a gas-burner. When the 

 part enclosed in the plethys- 



membrane of which is connected with mograph expands, air isSUCS 



FIG. 



DROMO- 



33. CHAUVEAU'S 

 GRAPH. 



A, tube connected with bloodvessel ; 



B, metal cylinder in communication 

 with A. The upper end of B has a 

 hole in the centre, which is covered by 

 a membrane, m, through which a lever, 



C, passes ; C has a small disc p, at its 

 end, which projects into the lumen of 

 A, and is deflected in the direction of 

 the blood-stream through A. The de- 

 flection is registered by a recording 

 tambour in communication by the tube 

 E with a tambour D, the flexible 



the lever or pendulum C. 



from the connecting tube, and 



