INFLUENCE OF THE CARDIAC NERVES ON THE FROG'S HEART 267 



hypoglossal away, and also to cut the brachial and the laryngeal nerves 

 to prevent the stimulation of undesired structures. 



FIG. 216. Arrangement of Apparatus for Studying the Contractions of the Strip of the 



Apex of the Ventricle. 



Prepare an induction coil, see laboratory experiments on muscle. Use 

 platinum electrodes of the Harvard pattern, set the coil for a mild stimulus 

 tested by the lips or the tongue, 

 lift up the vagus gently and lay 

 it on the platinum tips of the 

 electrodes. Take care that the 

 electrodes do not come in contact 

 with the adjacent tissue. Arrange 

 a signal magnet as shown in the 

 diagram, so that the magnet and 

 the stimulating key of the induc- 

 tion coil may be closed and opened 

 at the same instant. When all is 

 ready (a) secure a normal record, 

 then (b) stimulate the vagus for 

 five to ten seconds, recording the 

 time with the signal magnet and 

 allowing the record to continue 



until the heart has returned to its 



i T. j FIG. 217. Diagram Showing the Rela- 



normal rate and amplitude, -I.e., tions of the f vago-sympathetic Nerve to the 



Hy, Hypoglossal; Gl, 

 V, vago- 



usually one circuit of the drum. Heart, in the Frog. 

 Most students fail in this experi- 

 ment by 'not allowing sufficient 

 time in the record for a normal before stimulation, and by not allowing 



