PHYSIOLOGY OF THE CENTRAL 

 NERVOUS SYSTEM. 



LESSON LVIII. 



REFLEX ACTION ACTION OF POISONS- 

 KNEE-JERK. 



1. Reflex Action. Destroy the brain of a frog, which should 

 be done without loss of blood. Place under a bell-jar a normal 

 frog for comparison. Observe that immediately the frog is 

 pithed, on pinching one of its toes, very probably the leg will 

 not be drawn up. Allow the frog to rest for half an hour or 

 more, and observe 



(a.) Its attitude; the head of the. pithed frog lies on the 

 plate on which it is placed, while in the intact frog, the 

 head is erect, the body and head forming an acute angle 

 with the surface on which the frog rests. 



(6.) Its eyes are closed, while those of the intact frog are 

 open. The fore limbs are either flexed and drawn under 

 the chest, or spread out, so that the body is no longer sup- 

 ported on the nearly vertical fore limbs as in the intact frog, 

 but lies flat upon the surface of support. The legs are 

 pulled up towards the body. 



(c.) The absence of respiratory movements in the nostrils 

 and throat. Observe that it makes no spontaneous move- 

 ments, if left entirely to itself. 



(d.) Turn it on its back, it lies in any position it is 

 placed. Do this with a normal frog, the latter regains its 

 equilibrium at once. Pull out one of the legs, it will be 



