ACTION OF STRYCHNIA. 257 



4. Chemical Stimulation. 



(a.) In a small glass place some strong acetic acid and a 

 few pieces of filter paper 3 mm. square. Either when the 

 frog is lying on its back, or while it is suspended, apply 

 with a pair of forceps one of the pieces of paper moistened 

 with acid the surplus removed to the skin on the inner 

 side of the thigh. At once the leg on that side is violently 

 drawn up, perhaps both legs are drawn up, and the foot of 

 the leg first drawn up is swept over the spot stimulated, 

 as if to remove the piece of paper i.e., purposive, well- 

 co-ordinated movements are executed. At once dip the 

 frog in water to remove the acid, allow it to rest for some 

 time. 



(b.) After an interval of five minutes repeat the experi- 

 ment, but hold the leg to which the acid is applied. In all 

 probability the other leg will be moved, and the opposite 

 foot will be used to remove the irritating acid paper. Wash 

 the frog and allow it to rest. 



(c.) Test further by applying papers to the flank, the skin 

 over the gastrocnemius, c., and in all cases characteristic, 

 but different reflex movements will be elicited, if sufficient 

 interval for recovery (5 inins. at least) be allowed between 

 the successive experiments. 



(d.) With a needle destroy the spinal cord, all reflex 

 action is then abolished, although the nerves and muscles 

 retain their excitability, and the heart continues to beat. 

 Expose the heart and observe it beating. Test the excita- 

 bility of the nerves and muscles in the usual way with an 

 interrupted current. 



5. Action of Strychnia. 



(a.) Using a frog with iits brain destroyed, inject with a 

 fine glass pipette or a hypodermic syringe into the dorsal 

 lymph-sac a drop of dilute solution of sulphate of strychnia 

 (0'5 per cent.) 



(b.) Observe, that as soon as the poison is absorbed i.e., 

 within a few minutes cutaneous stimulation of any part of 

 the body, even tapping the table excites violent tetanic 



17 



