86 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



Study the character of the heart-beats occurring directly after the 

 inhibition. They may be small at first and gradually become larger, 

 or large at first, and slowly decrease to normal. No explanation can 

 be given for this difference. 



FIG. 54. RECORD OF THE CONTRACTIONS OF THE FROG'S HEART DURING STIMULATION 



OF THE VAGUS NERVE (TENSION LEVER). 

 The time is given in seconds, the stimulation is indicated by the signal. 



Stimulate the right vagus nerve with the same strength of current. 

 Do the nerves possess the same inhibitory power? They differ, but not 

 always in the same manner, i. e., the left or the right nerve may be more 

 powerful, but most generally the right. The same differences may be 



\ 



*. 



LAS 



FIG. 55. SCHEMA OF THE SYMPATHETIC NERVE IN THE FROG. 

 OC, Occiput; LAS, levator anguli scapula?; Rym, sympathetic; GP, glossopharyngeus ; 

 V-/S, vagosympathetic ; G, ganglion of the vagus; Ao, aorta; &A, subclavian artery. 

 (Stirling.) 



noted in the mammals. Occasionally a turtle will be found in which 

 neither vagus possesses this function. 



Stimulate either vagus nerve for three or four minutes. Note that 

 the heart "escapes" from the inhibition in a very short time, and sub- 

 sequently continues to beat in spite of the stimulation. 



