LVIIL] PERFUSION OF FLUIDS. 279 



apart. They will act as electrodes. Connect the other ends of the wires to 

 a Du Bois key introduced into the secondary circuit of an induction machine. 

 Arrange the primary coil for single induction shocks, introducing a Morse 

 key in the circuit. 



(6.) Make an "apex preparation," and place it on the electrodes on the 

 glass slide. Rest on the heart a heart-lever properly balanced and arranged 

 to record its movements on a slow-moving drum (5 mm. per second). The 

 preparation does not contract spontaneously, but responds to mechanical or 

 electrical stimulation. 



(c.) Stimulate the apex preparation with single break induction shocks at 

 intervals of about ten seconds. To do this, un-short-circuit the secondary 

 circuit, depress the Morse key, short-circuit the secondary circuit, and close 

 the Morse key again. Repeat this at intervals of ten seconds, and note that 

 the amplitude of the second contraction is greater than the first, that of 

 the third than the second, the fourth than the third, and then the successive 

 beats have the same amplitude (fig. 201). Allow the heart apex to rest for a 

 few minutes, and repeat the stimulation. Always the same result is obtained. 

 From the graduated rise of the first three or four beats after a period of rest, - 

 the phenomenon is known as the "staircase." The increment is not equal 

 in each successive beat, but diminishes trom the beginning to the end of the 



(rf.) If, while the apex is relaxing, it be stimulated by a closing shock, it 

 contracts again, so that the lever does not immediately come to the abscissa. 



(<?.) li the Morse key be rapidly tapped to interrupt the primary current, 

 the contractions become more or less fused, and the lever remains above the 

 abscissa writing a sinuous line. 



4. Effect of Destruction of the Nervous System on the Heart and Vas- 

 cular Tonus. 



(a.) Destroy the brain of a frog, and expose its heart in the usual way, 

 taking care to lose no blood ; note how red and full the heart is with blood. 



(6.) Suspend the frog, or leave it on its back, introduce a stout pin into the 

 spinal canal, destroy the spinal cord, and leave the pin in the canal to prevent 

 bleeding. Observe that the heart still continues to beat, but it is pale and 

 collapsed,, and apparently empty ; it no longer fills with blood. The blood 

 remains in the greatly dilated abdominal blood-vessels, and does not return 

 to the arterial system, so that the heart remains without blood. It the belly 

 be opened, the abdominal veins are seen to be filled with blood. 



(c.) Amputate one limb, perhaps not more than one or two drops of blood 

 will be shed, while in a frog with its spinal cord still intact, blood flows freely 

 after amputation of a limb. 



LESSON LVIII. 



PERFUSION OP FLUIDS THROUGH THE HEART 

 PISTON-RECORDER. 



1. Perfusion of Fluids through the Heart. 

 The Fluid. (a.) Take two volumes of normal saline, add one 

 volume of defibrinated sheep's blood, mix, and filter. See that 



