8 4 



THE MECHANISM OF THE CIRCULATION. 



volume of blood which has passed during * the period of observation, and this 

 volume, divided by the time and the sectional area of the artery, gives the 

 mean velocity per second. In using the stromuhr, the mean velocity in an 

 artery is found to vary greatly. This, for the most part, is owing to the 

 variations of resistance in the peripheral arterioles. During the operative 

 procedure the blood-flow must for a time be cut off by clips in order that 

 the tubes of the stromuhr may be introduced within the artery. From the 

 anaemia thus produced there results a temporary paralysis of the tone in the 

 arterioles. Variations of resistance arise when the blood-flow is re-established 

 and the tone commences to recover. By means of Ludwig's stromuhr, for 

 example, Dogiel x found the velocity to vary from moment to moment thus : — 



Tigerstedt has by means of the stromuhr been able to measure 

 directly in the rabbit the velocity of the blood-flow in the root of the 

 aorta, and thus the systolic output of the heart. Other instruments 

 have been invented for obtaining continuous records of the variations 

 of velocity of flow in any given vessel. Chauveau and Lortet, employ- 

 ing the principle of the hydrometric pendulum, constructed an instru- 

 ment of this kind, named the dromograph. 2 



As is seen in the diagram, this instrument consists of a chamber (B), which 

 communicates with a tube (A), and is closed at the top by a membrane. The 



tube (A) is inserted in the course of the artery 

 which is under investigation. In this tube 

 there hangs a small pendulum, which issues 

 through the membrane in the roof of the 

 chamber (B). The membrane affords a fulcrum 

 to the pendulum, and the movements of the 

 latter are brought to bear upon a tambour, 

 which communicates by an indiarubber tube 

 with the recording tambour (I>). 



If the mass of the pendulum be small, the 

 accuracy of this instrument is found to be considerable. Before use, the 

 excursion of the dromograph must be calibrated by recording the now of water 

 at known velocity through it. 



In Fig. 55 is shown the synchronous record obtained of the velocity 



1 Ba: d. k. Sachs. Gcsclhch. d. Wissensch., Math.-Phys. CI., Leipzig, 1867, S. 239. 

 - Joum. de physiol. de I'homme, Paris, 1860, tome iii. p. 695; Lortet, "Recti, sur la 

 vitesse du cours du sang," Paris, 1867. 



Fig, 54. — Diagram of Chauveau 

 and Lortet's dromograpli. 



