PRACTICAL EXERCISES 



203 





D 



(b) Dissect out the vago-sympathetic on one side in the neck of the 

 dog. The guide to the nerve is the carotid artery. These two struc- 

 tures and the internal jugu- 

 lar vein lie side by side in 



a common sheath. Feel 

 for the artery a little ex- 

 ternal to the trachea, cut 

 down on it, open the sheath , 

 isolate the vago - sympa- 

 thetic for about an inch, 

 pass two ligatures under it, 

 tie them, and divide be- 

 tween the ligatures. The 

 peripheral and central ends 

 of the nerve may now 

 be successively stimulated. 

 Stimulation of the peri- 

 pheral end causes slowing 

 of the heart, or stoppage 

 in diastole. Feel that it 

 softens when it stops. It 

 soon begins to beat again. 

 Stimulation of the central 

 end of the vago-sympa- 

 thetic may or may not 

 cause inhibition . 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, 

 withopened 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 prep- 

 aration so that the nerve 

 touches the heart also by 

 its longitudinal surf ace. At 

 each cardiac beat the nerve 

 is stimulated by the action 

 current (p. 833), 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 



P\U 



Fig. 95- Myocardiograph of Adami and Roy 

 (modified by Cushny and Matthews). AB, a 

 perpendicular rod descending from a universal 

 joint, which is not shown in the figure; CD, a 

 brass sheath, moving easily on the rod, and 

 bearing on its upper end an ivory pulley, and at 

 its lower end a horizontal bar, which is inter- 

 rupted by a plate of hard rubber, I. The per 

 pendicular rod EF moves on the horizontal bai 

 by the hinge-joint, J. EF is hooked at one end 

 for attachment to the heart, and bored at the 

 other for a thread which, passing over the pulley 

 at C, passes through the universal joint and 

 moves a writing lever not shown in the figure. 

 CD is prevented from moving up AB by a ring of 

 brass, G, which is screwed to AB, but is not 

 attached to CD ; the hook F can therefore move 

 to and from AB, and can rotate round it, while 

 it cannot move up or down. The hooks F and B 

 are insulated from each other by the hard rubber, 

 I. H is a binding post through which, and 

 through another connected with A, induction 

 shocks may be sent at will into the portion 

 of the heart lying between the hooks. 



