638 MANUAL OF PHYSIOLOGY. 



been removed, or the parts directly stimulated, and by noting the 

 symptoms produced in man by lesions of this part of the brain. 

 The former gives the most definite results, and therefore, for our 

 purpose, deserves most attention. 



When the cerebral hemispheres have been removed from a 

 frog, the animal retains the power of carrying out coordinated 

 motions of much greater complexity than those performed by 

 command of the spinal cord alone. But this power is not exer- 

 cised spontaneously. That is to say, the animal can balance 

 itself accurately, jump, swim, swallow, etc., but it only attempts 

 these acts when forced to do so by stimulations arising from its 

 outer surroundings. Thus on a flat surface it sits upright, but 

 does not stir from the spot where it has been placed ; if the sur- 

 face upon which it sits be inclined, so that its head is too low, it 

 turns round to regain its equilibrium. If the surface be further 

 inclined, it at first crouches so as not to slip off, and then crawls 

 upwards to find an even resting-place. Plunged into deep water, 

 it swims perfectly, but on arriving in a shallow part, it either 

 rests quietly with its nose out of the water and its toes touching 

 the ground, or crawls out to sit on the water's edge, where it finds 

 its balance. When touched on the leg, it jumps away from the 

 stimulus, and in so doing avoids any obvious dark obstacle. It 

 swallows if a substance be put in its mouth, but it does not 

 attempt to eat even when surrounded with food. In short, all 

 movements, even the most complex, may be brought about by 

 adequate stimulation spontaneity only is wanting. The pupil 

 responds by reflex contraction, when the retina is exposed to 

 light; the eyes are closed if the light be intense; and the head 

 may follow the motions of a flame moved from side to side. A 

 sudden or loud noise causes the animal to move. From the fore- 

 going facts, and the power such a frog has of avoiding a dark 

 object, we may conclude that the impulses arising from the spe- 

 cial sense organs are all duly received and excite more or less 

 elaborate response, but the consciousness of the arrival of these 

 impulses no longer exists. 



The removal of the hemispheres of birds and rabbits leaves the 

 animal in somewhat the same condition ; but the response to the 



