256 



EXPERIMENTAL PHARMACOLOGY 



respond? Stimulate the left gastrocnemius (through the 

 skin) directly. Does it contract? What conclusions can 

 you draw ? Where does curara act? Does your experiment 

 prove the nerve trunks are not paralyzed ? Are the sensory 

 nerve endings paralyzed J ? Does your experiment give you a 

 chance to test this point? Count the lymph heart rate 



Fig. 230. Tracing showing the action of a solution of curara dropped on the heart 

 of a frog. Lower line normal, showing the inhibition caused by stimulation of the 

 vagus trunk. Second line, curara was applied at "x" and the vagus was again stimulated 

 as shown by the short line and legend. Third line, the application of the drug was con- 

 tinued and the vagus trunk was again stimulated as indicated. No noticeable results fol- 

 low the stimulation. Why not? Fourth and fifth lines, application of the drug was con- 

 tinued and its action on the heart is shown. 



again. What conclusions can you draw from this ? What 

 is the action of curara on the central nervous system? (See 

 McGuigan : Journal of Pharmacology and Experimental 

 Therapeutics, 1916, viii, p. 471.) 



Do you know of any other substances possessing an ac- 

 tion on motor nerve endings in striated muscles like curara 

 does ? How does this drug differ from atropine in its action 

 on nerve endings ? 



