CIRCULATION OF THE BLOOD. 505 



This may be accomplished by the following experiment : 



A large dog should be rendered unconscious by a subcutaneous injection of 

 morphine, fastened securely on his back, and a long, slender, steel needle then 

 passed perpendicularly through the walls of his chest into his heart at the point 

 of greatest intensity of the cardiac impulse. Then, following the line of the ven- 

 tricle up to the aorta, three more steel needles should be inserted, one in each 

 succeeding intercostal space above the first, and then again one on each side of 

 the second needle, about one inch from it and in the same interspace. -Then it will 

 be seen that, although each of these needles moves at each contraction of the heart, 

 the movements described by their free ends widely differ. 



No. 1, inserted in the apex, merely quivers at each pulsation without describ- 

 ing any definite motion dependent upon the cardiac contraction, though it is seen 

 tolbllow the ascent and descent of the diaphragm. 



Nos. 2, 3, 4, inserted in the intercostal spaces above, describe an instantaneous 

 upward movement at each contraction, the degree of excursion of their free ends 

 being directly dependent upon their distance from No. 1. The fulcrum on which 

 each needle moves is its point of transfixion of the chest-wall ; therefore, an up- 

 ward movement of the free end of the needle indicates a downward movement of 

 the body in which the other end is inserted. Finally, Nos. 5 and 6 oscillate more 

 or less horizontally, their free ends receding from each other as well as from 

 No. 1 at each contraction of the ventricle. 



From these facts we learn that the apex, the point at which the car- 

 diac impulse is felt, is itself nearly motionless, while the base of the 

 heart at each ventricular systole approaches the apex, and that the other 

 parts of the ventricle are drawn toward the apex in a degree propor- 

 tionate to their distance from it, while, as seen in the exposed heart, the 

 shortening of the ventricles is compensated by the elongation of the 

 great vessels at the base. The impulse, therefore, is the hardening of the 

 ventricle, transmitted through the stationary portion which is in contact 

 with the chest-walls, through the chest-wall to the finger. It is improper 

 to speak of the impulse as a blow, as the apex never leaves the chest- 

 wall. But while this is so, there is, nevertheless, a certain amount of 

 motion in the apex which results in the elevation of the chest-wall at 

 the point of cardiac impulse. If an excised heart is placed on a hori- 

 zontal surface, the base of the ventricles in a state of diastole takes on 

 the form of an ellipse with its largest diameter horizontal, while the 

 apex falls until it is in contact with the supporting surface. When the 

 ventricle passes into systole the base of the heart passes from an ellip- 

 tical to a circular form, and since the apex takes a position in a line with 

 the central point of the base of the heart it leaves the surface on which 

 it rested and tilts forward, at the same time approaching the base from 

 the reduction in the length of the ventricles. The state of affairs is 

 somewhat similar while the heart is in its normal position in the 

 thorax. There the base of the heart takes on an elliptical form from 

 contact with the chest-walls, while the apex tends to fall away from the 

 chest. In systole, the base, assuming a circular form, must cause the apex 

 to move forward, and, so producing stronger pressure on the ribs, cause 

 the elevation which constitutes the cardiac impulse, the base descending 

 in systole as already described. 



