July 13, 1906.] 



SCIENCE. 



53 



due to intraventricular or to coronary pres- 

 sure, the heart was excised and the ventricles 

 slit open; injections under pressures varying 

 from 44 mm. to 200 nun. of mercury were then 

 made through the aorta and also directly into 

 the anterior coronary artery. On cessation 

 of the contractions following the external ap- 

 plication of the solution to the heart, per- 

 fusion through the coronary arteries was be- 

 gun, and with blood and its mixtures, oil, 

 hydrogen gas, and all solutions, rhythmical 

 beats followed, the magnitude and rate of 

 which varied with the pressure. The evi- 

 dence seems conclusive that there exists for 

 each solution a certain optimum pressure 

 which produces the maximum rate without a 

 diminution of the amplitude, and that this 

 optimum changes with the condition of the 

 heart. With hearts from the same species 

 of animals, the optimum pressure for each 

 solution may vary widely at corresponding 

 periods of the experiment. The actual change 

 in rate for a given change in pressure may not 

 be constant for different hearts under similar 

 conditions; nor for the same heart under dif- 

 ferent conditions. The rate may change 

 three hundred per cent, within the limits of 

 the pressure used, variations occurring when 

 the pressure is changed (1) from low to high, 

 or (2) from, high to low. Increase in pressure 

 may be considered as a stimulation in the ordi- 

 nary sense of the term, for the reason that an 

 increase above the optimum causes an increase 

 in rate, and that delirium cordis may be pro- 

 duced if the pressure be raised sufficiently 

 high. If the pressure now be gradually low- 

 ered a regular rhythm returns, which becomes 

 slower concomittantly with the fall in pres- 

 sure. With the same heart, several successive 

 increases and decreases of pressure m_ay cause 

 nearly identical rhythms at corresponding 

 pressures, the gradual increase or decrease of 

 pressure being attended by a fairly constant 

 change in rate for corresponding changes in 

 pressure. A sudden and profound fall in 

 pressure may cause either (1) an immediate 

 increase in rate succeeded by a decrease to the 

 rate previously observed for that pressure, or 

 (2) a slowing of the rate, even to total cessa- 

 tion, succeeded by a return to the rate pre- 



viously observed for that pressure. The first 

 phenomenon bears some resemblance to that 

 following a sudden fall of blood pressure in 

 the intact animal, i. e., acceleration, and the 

 second bears a striking resemblance to vagus 

 inhibition in the intact heart. In the pre- 

 liminary experiments with the heart in situ 

 the higher cardiac nerve centers were inactive. 

 When the animal is under light anaesthesia, 

 the changes in rate produced by changing the 

 pressure, both before and after section of the 

 cardiac nerves, are not the same as in the 

 isolated heart, or in the resuscitated heart in 

 situ. The changes in the rhythm are not due 

 to alterations in intraventricular pressure. If, 

 in the turtle, the cannula is introduced di- 

 rectly into the ventricle the beat may be prac- 

 tically stopped, owing, presumably, to disten- 

 tion of the ventricle. Eree incision of the 

 ventricles in the excised mammalian heart 

 precluded any distention. 



With hearts in situ, and in good condition, 

 following injection of blood dilutions into the 

 aorta, the left ventricle got up a pressure 

 greater than that used for injecting. In no 

 instance were efficient contractions obtained by 

 injecting artificial solutions alone. Their use 

 appears to cause a rapid deterioration of 

 cardiac tissue as regards its susceptibility to 

 restoration and efficiency, though complete 

 loss of irritability may not occur for a long 

 time; e. g., from strips of cats' ventricles 

 bathed in Locke's solution, tracings were 

 taken showing contractions for a period of 

 more than six hours, at which time the experi- 

 ment was discontinued. Efficient contrac- 

 tions, maintained for relatively long periods, 

 followed the injection of defibrinated blood or 

 blood dilutions. If the perfusion with arti- 

 ficial solutions had not been too prolonged, 

 the hearts could be restored to fairly good con- 

 dition by perfusion with blood mixtures. The 

 optimum pressure for blood and its dilutions 

 was considerably higher than that for the 

 artificial solutions. This difference may be 

 due in part to a difference in viscosity, but it 

 is also possible that artificial solutions increase 

 the excitability of the preparation by direct ac- 

 tion primarily on the vessel walls. Two facts 

 lend some support to this view: (1) bathing 



