CHAPTER VIII. 

 THE PHYSIOLOGY OF THE NERVOUS SYSTEM. 



I. REFLEX ACTION. 



1. Material and Appliances. Three large, vigorous frogs; operat- 

 hig~case; sulphuric acid, 0.5 per cent.; acetic acid, 50 per cent.; dis- 

 tilled water; cork beard, 10 cm. square; hand basin; filter paper; 

 six watch-glasses. 



2. Preparation. Pith two of the frogs, taking care to sever the 

 medulla completely; destroy the brain but leave the spinal cord intact. 

 If there is hemorrhage plug the puncture with absorbent cotton. 

 Lay the pithed frogs ventrum down, with legs extended, upon a 

 moist paper, Jsfote that if the toes be pinched the leg will not be 

 flexed. There is no reflex response. The animal is under the in- 

 fluence of shock. This condition will probably last for half an hour 

 or more. Recovery will be indicated by the drawing up of the legs, 

 first one leg and then the other being flexed. 



3. Observations, a. Modifications of General Functions by Pithing. 

 (1) The pithed frogs lie upon the ventrum with legs flexed. The 

 position simulates the normal. Make a detailed comparison of 

 the posture of the pithed frogs with that of the normal frog under 

 the bell-jar. 



(2) Compare pithed frogs with normal as to the appearance of the 

 eyes. 



(3) Study the respiratory function of the pithed frogs. 



(4) Is the heart, as observed through the body wall, acting with 

 usual rate and force in the pithed frogs? 



(5) Gently lower a pithed frog into a basin of cold water. Is 

 there an adaptation to the conditions? Does the frog swim? Vary 

 the experiment by dropping the frog from a height of six inches. 

 Take a yard of cord and tie one end around the brachium of the 

 normal frog. Repeat the experiments with the normal frog and 

 note the character of response. 



(6) Place a pithed frog upon a cork board; gently tip the board 

 in any direction, noting whether there is adaptation in equilibration. 

 Repeat the experiment with the normal frog. Describe differences. 



(7) Lay a pithed frog on its back on the table; will it right itself? 

 Try a normal frog. 



