NERVOUS SYSTEM. 



6. Apparent Purposive Character of Reflex Responses. 



A pithed frog is prepared as in the previous experiments. Take 

 a small piece of filter paper wet with acetic acid diluted one-half 

 with water, and apply this to the ventral aspect of one thigh. Note 

 the attempt to remove this with the foot of the same side. If this 

 is unsuccessful, or if the leg be held fast, the foot of the opposite 

 side will be brought into play and even the fore limbs, in an attempt 

 to brush off the offending irritant. 



6. To Show the Centres of Reflex Exchange in the De- 

 cerebrized Frog. Using the frog of the previous experiment, 

 run a long needle through the neural canal to destroy the spinal cord. 

 After a sufficient interval, test the frog as before for reflexes. Result ? 

 What is the function of the cord in relatioli to reflex action? 



Test the excitability of the muscles and nerves with the induced 

 current. Open the thorax and observe the beating of the heart. 

 The frog is still alive so far as the vegetative functions are con- 

 cerned, but the entire cerebro-spinal axis is destroyed and conse- 

 quently all reflex action is abolished. 



7. Action of Strychnine. Decerebrize a frog. Test the re- 

 flexes as in experiment 2. Now inject under the skin a solution 

 containing one-half milligram of strychnine sulphate. Test re- 

 flexes again, as before, at five-minute intervals. If there is no ap- 

 preciable change after ten minutes, repeat the injection. What 

 is the effect upon reflex time as compared with the normal for 

 the frog used ? 



Repeat the injection until the frog is thrown into tetanic spasms 

 upon the slightest stimulation. What is the character of these 

 spasms? What is the position of the frog during a convulsion? 

 Explain. 



Now destroy the cord by passing a needle through the neural 

 canal. What is the effect upon the strychnine spasms ? What is 

 the seat of the strychnine action ? 



8. Action of Chloral Hydrate. Pith another frog. Estab- 

 lish the normal reflex time to some stimulus, taken as a stand- 

 ard. Inject under the skin 10 drops (about 0.6 c.c.) of a 2-per- 



4 [49] 



