viii BLOOD-STEEAM: MOVEMENT IN VESSELS 275 



section on the right. The tube TT is intended for insertion in 

 the carotid artery of a horse or other large animal ; L represents 

 the bar of the pendulum which ends in a very light plate or disc 

 p, dipping into the axis of the blood-stream. The bar of the 

 pendulum passes at m through a rubber membrane, which acts 

 as a pivot to the pendulum, and is then prolonged externally till 

 it joins a Marey's air tympanum. The tube TT has a narrow 

 longitudinal cleft along which the terminal disc of the pendulum 

 can move, in accordance with the oscillations of current velocity ; 

 these are reversed at the membrane of the receiving tambour, 

 which again transmits them to a tambour with a writing lever. 

 No blood can enter the groove in which the bar of the pendulum 

 oscillates freely, because it is connected with an external space 

 filled with an alkaline solution through the side tube B, and then 

 closed with a clamp. The sphygmoscope S is applied at the side 

 of the tube TT, and records the oscillations of pressure on a 

 revolving cylinder by means of a second writing tambour which 

 acts synchronously with the first. 



Just as sphygmograms do not give absolute values of oscilla- 

 tions of blood pressure, so the tachygrams or dromograms recorded 

 by Chauveau's haeniodroinograph yield only relative values of the 

 oscillations of current velocity above and below the zero line, 

 which is reached when there is no movement, because the disc of 

 the pendulum is under ecpial pressure on both sides. In order to 

 ascertain the absolute value of velocity and its oscillations, the 

 apparatus must be graduated. Chauveau did this by sending a 

 stream of water through it, of which the outflow was regulated 

 until the deflections of the pendulum attained the maximal, 

 minimal, and mean values obtained on applying the apparatus to 

 the carotid of the horse. It is then easy to determine the velocity 

 corresponding to these points, by calculating it from the diameter 

 of the arteries, and from the respective amount of outflow, obtained 

 with different degrees of deflections of the pendulum. 



Ohauveau and his pupils Bertolus and Leroyenne were able to 

 determine that the velocity of the blood-flow amounted to 520 mm. 

 per second in the carotid of the horse during systole, to 220 mm. 

 during the dicrotic wave, and to 150 mm. during diastole. 



When the carotid is ligatured on one side, a compensatory rise 

 of velocity is visible in the other carotid. During the masticating 

 movements also, in consequence of a dilatation of the vessels of 

 the masticatory muscles and salivary glands, there is an increase of 

 circulatory velocity in the carotid, which may become five or six 

 times greater than the initial value. When any considerable 

 vascular dilatation is produced by dividing the spinal cord, the 

 rate of flow is considerably augmented during systole, but becomes 

 extremely low during diastole. At the end of diastole the 

 velocity is greater in the peripheral than in the central arteries ; 



