176 ESTIMATION OF THE CAPACITY OF THE VENTRICLES. 



dromograph. Fig. 69 III shows the velocity-curve taken from the 

 carotid of a horse and which corresponds with the pulse-curve in 

 indicating the primary elevation (P), as well as the dicrotic elevation 

 (R). Examination of an extremity with the plethysmograph also 

 discloses this velocity-pulsation or volume-pulsation. In the small 

 arteries an additional pulsatory acceleration is observed, which occurs 

 more rapidly in the first phase than in the later ones. The small trunks 

 themselves are not visibly distended under such circumstances. As 

 the capillary region is approached this phenomenon, ..like the pulse- 

 movement in general, disappears. 



In the arteries the velocity must be retarded by each inspiration 

 and increased by each expiration; but the differences here are exceed- 

 ingly small. 



If what has been said in the foregoing concerning the influence of the respira- 

 tory pressure on the dilatation and contraction of the heart, and, therefore, on the 

 movement of the blood, be compared, it will be evident that the respiration must 

 also have an accelerating influence on the blood-current. Likewise, artificial 

 respiration has the same effect: When artificial respiration is suspended in a 

 curarized animal, the blood-current at once becomes slower. If, however, the 

 suspension is continued for some time, the current becomes again accelerated 

 in consequence of the resulting dyspneic irritation of the vasomotor center. 



In the veins many derangements in the uniform flow of the blood 

 occur : i . Regular fluctuations caused by respiration and the movements 

 of the heart at the points where the large trunks empty into the heart. 

 2. Irregular effects due to pressure, friction in the direction of the 

 current or in the opposite direction, changes in the position either of 

 the body or of the limbs, a pump-like action in the iliac vein due to 

 walking, etc. During extension and outward rotation of the thigh the 

 crural vein relaxes and collapses in the iliac fossa and the internal 

 pressure becomes negative; while when the thigh is flexed and elevated, 

 the vein becomes filled to distention and the pressure rises. By means 

 of this pump-like action the blood (with the aid of the valves) is forced 

 upward. A somewhat similar phenomenon takes place during walking. 



ESTIMATION OF THE CAPACITY OF THE VENTRICLES FROM 



THE CURRENT- VELOCITY BY THE METHOD OF 



CARL VIERORDT. 



There may be considered at this point Vierordt's attempt to estimate the 

 capacity of the ventricles, which is based on the velocity of the blood-current 

 in the innominate artery, in the aorta immediately before the origin of this trunk ^ 

 as well as in the coronary arteries; although his ^premises are exceedingly 

 uncertain. 



(a) The velocity of the current in the right carotid is 26.1 cm. in a second; 

 the cross-section of the vessel is 0.63 square cm.; hence, the quantity of blood 

 that flows through it is 26.1 X 0.63 = 16.4 cu. cm. (i). 



(&) The velocity of the current in the right subclavian artery is 26.1 cm. a 

 second; the cross-section of the vessel is 0.99 square cm.; hence, the quantity of 

 blood that flows through it is 26.1 cm. X -99 = 2 5-8 cu - cm - ( 2 ) By adding i 

 and 2 the quantity of blood that flows through the innominate artery is obtained: 

 16.4 + 25.8 = 42.2 cu. cm. The cross-section of this artery is 1.44 square cm. 



(c) The cross-section of the aorta immediately before the origin of the in- 

 nominate artery is 4.39 square cm.; the velocity of the current in the aorta is 

 estimated to be about one-fourth greater than in the innominate, that is, 36.6 

 cm.; hence, the quantity of blood that flows through it is 161 cu. cm. (3). 



(d) The quantity of blood that flows through the two coronary arteries may 

 be assumed to be 4 cu. cm. (4). Hence, the entire quantity of blood that flows 



