ACTION ON THE HEART OF THE FROG. 219 



(6.) Expose the heart and attach its apex to a lever sup- 

 ported by an elastic thread as in Gaskell's method. Record 

 several contractions, and then stimulate the sympathetic 

 with interrupted shocks by means of fine electrodes. The 

 heart beats quicker. If the heart is beating quickly, reduce 

 the number of beats by cooling it. 



(c.) If desired, the vagus may be isolated and stimulated, 

 and the effects of the two nerves compared (although the 

 vagus outside the skull is really the vago-sympathetic). 



Fig. 100. Scheme of. the Frog's Sympathetic. LAS, Levator anguli 

 scapulae ; Sym, sympathetic ; GP, glossopharyngeal ; V-S, vago-sym- 

 pathetic ; G, ganglion of the vagus ; Ao, aorta ; SA, subclaviau artery 

 (Gaskell). 



Stimulation of the intra-cranial vagus i.e., before it is joined 

 by the sympathetic is somewhat too difficult for the average 

 student, and is therefore omitted here. 



LESSON XLYIII. 



ACTION OF DRUGS AND THE CONSTANT 



CURRENT ON THE HEART DESTRUCTION 



OF THE CENTRAL NERVOUS SYSTEM. 



1. Action of Drugs on the Heart Muscarin and Atropin. 

 Either the excised heart, placed in a watch-glass, or the heart, 

 in situ, may be used. 



