B. XERYE CELLS. (PHYSIOLOGY OF CENTRAL XLR- 

 VOUS SYSTEM 1.) 



A. REFLEXES. 



214. In a normal frog observe the following: Movements of the 

 head when the animal is revolved in ( i ) a vertical plane parallel to 

 the axis of the body, (2) in a vertical plane perpendicular to axL 

 of body, (3) in a horizontal plane. Make a general statement 

 denning movements in the above cases. 



215. Pith a frog (brain only) and stimulate by pinching or 

 touching the following regions : a toe of right foot : a toe of 

 left foot ; a finger ; an eye ; the skin of the abdomen. Record 

 the movements resulting in each case. 



216. Record what happens in the following reflexes in yourself 

 or partner: Pupil rcflc.rcs. (i) Light reflex. Close one eye for 

 several seconds, then open it quickly. Xote any change in pupil. 

 (2) Consensual reflex. Close one eye as before, but watch the pupil 

 of the other eye when the first is opened again. ( 3) Accommodation 

 reflexes. Look, alternately at a near and a far object. Xote any 

 change in pupil. This experiment cannot be performed on yourself. 

 (4) If you are not already familiar with the "knee jerk", demon- 

 strate this. 



217. Purposiveness of rcflc.rcs. Suspend from a hook a frog 

 with its brain pithed. Dip in acetic acid a piece of filter paper about 

 a quarter cm. square. Shake oft" the excess of acid, then apply the 

 paper to the front of the frog's body, \Yhat movements result? 

 Remove the paper, dip the frog in water to remove the acid from his 

 skin, and again suspend the animal from the hook. After five 

 minutes repeat the experiment, but apply the acidulated paper to 

 the inside of the thigh. If only one foot is drawn up hold that 

 foot. Does the other foot now move? After washing off the 

 acid and waiting again for five minutes, apply the acidulated paper 

 to the back near the tip of the urostyle. To what region is the re- 

 sponse now directed? Are the directions of the reflex movements 

 sufficiently different in these three instances, and pointed toward a 

 definite end with sufficient clearness, to indicate purposive action ? 



Are the reflexes in sections 214, 215, and 216 obtained when the 

 spinal cord is also destroyed J . 



218. Summation. Suspend by a hook a frog with brain pithed. 

 Tie two fine copper wires i cm. apart around the left foot, near 

 the toes, and attach the wires to a secondary coil of the inductorium. 



