CENTRAL NERVOUS SYSTEM. . 709 



ness, stronger and stronger stimuli being required to induce a reaction. This 

 holds true down to the anterior end of the bulb, the removal of which, on the 

 contrary, sets free the lower centres, so that the frog becomes incessantly active. 

 Just how this release is effected is not easy to explain, but further removal is 

 again followed by the loss of responsiveness. 



Passing next to the bird, as represented by the pigeon, the observations of 

 Schrader are the most instructive. 1 The removal of the hemispheres from the 

 bird (see Fig. 202) involves taking away the mantle and the basal ganglia, the 



FIG. 202. Schema of the encephalon of a bird (Edinger). The oblique black line marks off the 

 structures in front of the thalamus. 



chiasma and the optic nerves being left intact. For the first few days after 

 operation the bird is in a sleep-like condition. Next the sleep becomes broken 

 into shorter and shorter periods, and then the bird begins walking about the 

 room. From the beginning its movements are directed by vision; slight 

 obstacles it surmounts by flying up to them, larger ones it goes around. In 

 climbing its movements are co-ordinated by the sense of touch, and the normal 

 position of the body is maintained with vigor. The birds which walk about 

 by day remain quiet and asleep during the night. In flying from a high 

 place the operated pigeon selects the point where it will alight, and prefers a 

 perch or similar object to the floor. 



A reaction to sound is expressed by a start at a sudden noise, like the 

 explosion of a percussion cap. 



Pigeons without the cerebrum do not eat voluntarily, though the presence 

 of the frontal portions of the hemispheres is sufficient to preserve the reaction. 



In a young hawk slight damage to the frontal lobes abolished for the time 

 the use of the feet in the handling of food, and thus abolished in this way the 

 power of feeding as well as that of standing. 



With the loss of the cerebrum the pigeon does not lose responsiveness to 

 the objects of the outer world, but they all have an equal value. The bird is 

 1 Archiv fur die gesammte Physiologic, 1888, Bd. xliv. 



