328 PRACTICAL PHYSIOLOGY. [LXX 



makes no spontaneous movements, although it responds readily to external 

 stimulation. 



{b. ) Its eyes are open and its respiratory movements continue (p. 311 ). 



(c. ) If placed on its back, it immediately rights itself. If placed on the 

 palm of the hand, or on a rough board held horizontally, it sits immovable, 

 but if the board be tilted, or the hand rotated, then, when a certain angle is 

 reached, its equilibrium is disturbed, and it begins to crawl up, until it comes 

 to the tx)p, where its equilibrium is restored, and there it sits motionless. 



(d.) If placed in water it makes continuous swimming movements. 



{e.) It will avoid an opaque object placed in front of it, when one causes it 

 to jump by pinching its hind-legs. 



(f. ) If held up between the thumb and forefinger of the right hand behind the 

 forearm, and if it be pinched, then it responds to every pressure by a " croak." 

 This is due to reflex excitation of the croaking centre. It also croaks on 

 stroking the skin of the back or flanks, 



{g. ) It does not feed itselfl 



9. Optic Lobes (Inhibition). 



(a.) Expose the optic lobes in a frog, after removing the cerebral hemi- 

 Bpheres. After recovery, determine the latent })eriod of a reflex mechanical 

 response of the legs by Tlirck's method (Lesson LXVIIL). 



{b. ) Apply a crystal of common salt to the optic lobes, and then determine 

 the latent period. It is greatly increased, or the reflex may be suppressed 

 altogether. 



