416 ON SOME FUNCTIONS OF THE ENCEPHALON. 



described. This attitude is the one to which the frog with 

 cerebellum and medulla clings most rigidly, to which it always 

 returns after being disturbed, and in which it eventually dies 

 if left alone and not fed. 



olia. II. Influence of the presence of optic lobes. Remove 

 llu- parts in front of the optic lobes as directed; the best re- 

 sults are obtained when the animal is allowed to remain per- 

 fectly quiet for a day, or for several hours at least, after the 

 operation. 



All the facts mentioned in 06s. I. may also be observed in 

 this case ; in addition, there are certain phenomena which are 

 only witnessed when the optic lobes are present. 



Goltz^ Balancing Experiment. Place the frog on a rough 

 board (about eight or nine inches square), somewhat near to 

 one of the edges. Hold the board horizontal, and the frog 

 will remain motionless in the normal attitude. 



Tilt the board gradually up, with that edge uppermost which 

 is farthest away from the frog, and towards which he should 

 be looking. Up to an angle of about 45 and beyond no 

 change will be observed in the frog. As soon, however, as 

 the board becomes so much inclined that the centre of gravity 

 of the frog is thrown outside the lower edge, the frog will 

 begin to creep up the board. As the inclination proceeds, the 

 frog moves higher and higher up, until, when the board at last 

 becomes vertical, the frog will be found seated in the normal 

 attitude, on the upper edge. On continuing the movement 

 of the board, so that what was the upper surface becomes the 

 lower, the frog will move from the edge downward over the 

 now upper surface ; and when that surface, by the continuance 

 of the revolving motion, again becomes inclined upward, will 

 again creep over it as before towards the new upper edge. 



Evidently here the disturbance of the centre of gravity pro- 

 duces such an effect as to give rise to movements which are 

 directed towards the re-establishment of equilibrium, and which 

 are continued until that result is achieved. At first sight this 

 may appear very much like an act of conscious intelligence, but 

 if the student carefully observes the different behavior of an 

 entire frog and of a frog in this condition, the contrast between 

 the two will be found very striking. This frog does nothing 

 but crawl, and stops crawling as soon as the stimulus of the 

 disturbed equilibrium passes away. When the experiment is 

 successful, he remains perched motionless on the edge of the 

 vertical board, and never leaps away. The entire frog leaps 

 ;u\ ay at once. 



f/W/2'.s Croaking Experiment. Place the frog on the table, 

 and with the thumb and forefinger gently stroke down the 

 flanks on either side. A little very gentle pressure must be ex- 

 ercised. As the thumb is thus carried backward along the 



