296 LAB OR A TOR Y G UIDE IN PHYSJOL Of Y. 



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

 What part protected from it? Illustrate by diagram. 



() Were strychnin a convulsant through its action 

 on the sensorium, would the legs be equally con- 

 vulsed ? 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 strychnin ? 



(3) Using as a guide the thread formerly passed around 

 it, pick up sacral plexus and sever it high up. 



(#) Does the strychnin reach the motor nerve and 

 muscles of uninjured leg ? 



() If strychnin were a convulsant through its action 

 on either the motor nerves or the muscles, or both, 

 would the uninjured leg still participate in the con- 

 vulsions ? 



(c) Demonstrate that muscles, sciatic nerve and sacral 

 plexus below the point at which it was severed, are 

 still intact, by stimulating distal portion of latter. 



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

 ' ited the possible action of strychnin ? 



(4) Expose the heart of a frog and ligate the aortae at 

 the base. Operation as follows : 



Freely expose sternum by -f- 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 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 forward. This gives 

 ready access to bulbus arteriosus and aortas. With an aneurism needle 

 pass fine thread around latter, taking care not to injure auricles, and 

 ligate. 



With scalpel cut through occipito-atlantoid membrane, from side to 

 side, and bend head forward. Remove posterior wall of upper end of 



