374 THE OUTGO OF ENERGY 



Note the level below which no section can be 

 made without rendering the reflex impossible. 

 The nerve cells concerned in this reflex lie on 

 the caudal side of this line. 



Now in a second frog make transverse sections, 

 beginning at the caudal end of the cord, and test 

 the reflexes as before, until the level is reached 

 beyond which a section will destroy the reflex. 



Observe that the portion of the cord comprised 

 between the two levels determined forms a seg- 

 ment which contains the central apparatus con- 

 cerned in the reflex studied. 



Reflexes in Man. 1. From the Skin. Rub 

 the plantar surface of the foot gently with some 

 hard object. 



The foot will be retracted reflexly. 



Similar results may be obtained by rubbing 

 the skin of the inside of the thigh, which will 

 cause contraction of the cremaster muscles ; or by 

 rubbing the skin of the abdomen, which will be 

 followed by contraction of the abdominal muscles. 



These reflexes are of importance in clinical 

 diagnosis because by means of them the seat of a 

 diseased area in the central nervous system may 

 sometimes be defined, since the reflex depends on 

 the integrity of the corresponding reflex arc. 



2. Cornea Reflex. Touch the cornea gently 

 with a thread. 



