PRACTICAL EXERCISES 179 



If it does, expose the other vago-sympathetic, divide it, and repeat 

 the stimulation of the central end. There will now be no inhibition 

 of the heart. Incidentally it may be seen that stimulation of the 

 central end of the vago-sympathetic causes strong, though, of course, 

 with opened chest, abortive, respiratory movements. 



(c) Pith a frog (brain and cord), dissect out the sciatic nerve on 

 one side up to the sacral plexus. Cut off the whole leg. Drop the 

 cut end of the nerve on the heart, and hold the preparation so that 

 the nerve touches the heart also by its longitudinal surface. At 

 each cardiac beat the nerve is stimulated by the action current 

 (Chap. XL), and the muscles of the leg contract. 



(d) Raise the board so that the head of the animal is down and 

 the hind-feet up, and note whether there is any effect on the action 

 and filling of the heart. Repeat the observation with head up and 

 feet down. 



(e) Compress the aorta with the fingers, and observe the effect on 

 the degree of dilatation of the various cavities of the heart. Repeat 

 the experiment with the inferior vena cava, and compare the 

 results. 



(/) Stop the artificial respiration, and observe the changes which 

 take place in the auricles and ventricles, comparing particularly the 

 right side of the heart with the left. Before the heart has stopped 

 beating, recommence the artificial respiration. 



(g) When the heart is again beating with a fair degree of regularity 

 and strength, make a small penetrating wound with a scalpel in the 

 left ventricle. Observe the course of the haemorrhage, and note 

 especially the difference in systole and diastole. 



(h] Lay the electrodes on the heart, and stimulate it with a strong 

 interrupted current. The character of the contraction soon becomes 

 profoundly altered. Shallow irregular contractions flicker over the 

 surface, with a kind of simmering movement suggestive of a boiling 

 pot (delirium cordis, fibrillar contraction). Now kill the animal by 

 stopping the artificial respiration. Observe how long the heart 

 continues to beat, and which of its divisions stops last. 



(/) Make a dissection of the cervical sympathetic up to the superior 

 cervical ganglion, and down through the inferior cervical ganglion to 

 the stellate or first thoracic ganglion. Make out the annulus of 

 Vieussens and the cardiac sympathetic (accelerator) branches going 

 off from the annulus or the inferior cervical ganglion to the cardiac 

 plexus (Fig. 50, p. 139). 



13. Action of the Valves of the Heart. (i) Study the action of 

 the valves of the ox-heart in the artificial scheme. Connect the ox- 

 heart provided with the pump P and bottle B, as shown in Fig. 67. 

 The cavity of the heart is illuminated by means of a small electric 

 lamp, the wires of which pass in at A. When the piston of the pump 

 is pushed down, water is forced through the aorta D along the tube 

 T into the bottle, and flows back again into the left auricle by the 

 tube T'. During each stroke of the pump the auriculo-ventricular 

 valve is seen through the glass disc inserted into C to close, and the 

 semilunar valve is seen through the glass in D to open. When 



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