210 



CIRCULATION OF THE BLOOD 



can calculate the volume of blood which flows through the artery in a certain 

 time. Registering current clocks have been devised by Ludwig and Hiirthle. 



In order to determine the variations of speed accompanying a single heart 

 beat, Vierordt employed a hydrometric pendulum. If a pendulum be hung in 

 a current of fluid, the length of its swing will depend on the linear velocity of 

 the current, and on a small scale it will reproduce correctly all the variations 

 of speed. Chauveau connected this pendulum with a writing 1 tambour and by 

 this means registered directly the variations in speed, and after graduating the 

 instrument, determined their absolute values (Fig. 81). 



The following results may be mentioned. The amount of blood expelled 

 per second by the left heart of a rabbit (of 1.59 kg. body weight) into the 

 aorta is on the average 1.35 c.c. The extremes in a series of fourteen experi- 

 ments were 0.91 and 3.76 c.c., the mean was 2.10 c.c. The mean linear velocity, 



FIG. 82. Velocity curve V and pressure curve P, carotid of the horse, after Lortet. The 

 lines 1, 2, 3, 4 give the corresponding points on the two curves. At 1 the blood is forced 

 into the aorta; between 3 and 4 the semilunar valves are closed. 



calculated from the diameter of the cannula tied into the aorta was 128 mm. 

 per second (extremes 72 and 340 mm.). 



During systole it is evident that the velocity is greater than during diastole 

 (cf. Fig. 82). In the carotid of the horse Lortet found 520 mm. per second 

 in systole and 150 mm. per second in diastole. At the end of diastole the 

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

 beginning of systole it increases considerably in the central and only slightly 

 in the peripheral. 



In dogs with a mean body weight of about 14 kg. Tschuewsky found for 

 the velocity in the carotid and crural arteries the values summarized in the 

 following table: 



