THE PHYSIOLOGY OF THE NERVOUS SYSTEM 2ll 



(a) Record the condition before and symptoms as they arise after 

 exhibition of the drug, especially with reference to: 

 (I) Muscular activity. Describe convulsions. 

 (II) Respiration. How affected by reflexes. 



(III) Circulation. Rapidity and rhythm of heart. 



(IV) If death occurs, which stops sooner, the circulation or 

 respiration ? 



(6) Formulate results. 



(2) Ligate thigh of frog, except sciatic nerve, at junction with 

 body. Sever all structures, except nerve and femur, just below 

 ligature. Separate cut surfaces with rubber tissue to prevent diffu- 

 sion of the drug. Turn the frog over and make a median abdominal 

 incision. Pressing viscera aside, pick up the sacral plexus of nerves 

 going to the uninjured leg. The sacral plexuses may be readily recog- 

 nized, lying on each side of the median line. Pass a thread loosely 

 around the nerves, so as to quickly find them when wanted. Inject 

 into dorsal lymph space 0.0001 grm. strychnine. 



(a) What part of the frog is reached by poison? What part is 

 protected from it? Illustrate by diagram. 



(6) Were strychnine a convulsant through its action on the sen- 

 sorium, would the legs be equally convulsed? If it acted on the 

 spinal cord? If it acted on the motor nerves? If it acted on the 

 muscles directly? 



(c) Are both legs convulsed? 



(d) To what parts in the reflex arc have you limited the action of 

 the strychnine? 



(3) Using as a guide the' thread formerly passed around it, pick 

 up the sacral plexus and sever it high up. 



(a) Does this strychnine reach the motor nerve and the muscles 

 of the uninjured leg? 



(b) If strychnine were a convulsant through its action on either 

 the motor nerves or the muscles, or both, would the uninjured leg 

 still participate in the convulsions? 



(c) Demonstrate that muscles, sciatic nerve, and sacral plexus 

 below the point at which it was severed are still intact by stimulating 

 distal portions of the latter. 



(d) To what elements of the reflex arc have you limited the pos- 

 sible action of strychnine? 



(4) Expose the heart of a frog and ligate the aortse at the base. 

 Operation as follows: 



Freely expose sternum by + shaped incision and laying back of 

 flaps. Remove lower half of sternum with scissors, taking care not 

 to injure vessel in abdominal wall, which comes just to the tip of 

 sternum. Freely incise exposed pericardium, bringing heart into 

 view. Grasp apex of heart with forceps, taking care not to use force 

 enough to cut through ventricular wall, and draw heart down and 



