1004 WITHOUT CEREBRAL HEMISPHERES. [BOOK HI. 



voluntary movements. The bird never flies up from the ground, 

 never spontaneously picks up corn, and its aimless, monotonous, 

 restless walks, resembling the continued swimming of the frog 

 thrown into the water after being deprived of its cerebral 

 hemispheres, forcibly suggest that the activity is the outcome 

 of some intrinsic impulse generated in the nervous machinery 

 in some way or other, but not by the working of a conscious 

 intelligence as in the impulse which we call the will. 



Still we must not shut our eyes to the fact that spontaneous 

 movements, whatever their exact nature, are manifested by a bird 

 in the absence of the cerebral hemispheres, and become the more 

 striking the more complete the recovery from the passing effects 

 of the mere operation. Could such birds be kept alive for any 

 considerable time, possibly further developments might be wit- 

 nessed, and indeed cases are on record where birds have been 

 kept alive for months after the operation, and have shewn sponta- 

 neous movements of a still more varied character than those just 

 described ; but in such cases the removal of the hemispheres has 

 not been complete, portions of the ventral regions being left 

 behind ; and, though a mere remnant left around the optic thalami 

 can hardly be regarded as a sufficient cause for the spontaneity of 

 which we are speaking, a larger mass, still more or less retaining 

 its normal structure, might have a marked effect. And we may 

 here perhaps remark that all these facts seem to point to the 

 conclusion that what may be called mechanical spontaneity, 

 sometimes spoken of as 'automatism/ differs from the sponta- 

 neity of the 'will' in degree rather than in kind. Looking at 

 the matter from a purely physiological point of view (the only 

 one which has a right to be employed in these pages), the real 

 difference between an automatic act and a voluntary act is that 

 the chain of physiological events between the act and its physio- 

 logical cause is in the one case short and simple, in the other long 

 and complex. We have seen that a frog lacking its cerebral 

 hemispheres, viewed from one stand point, appears in the light of 

 a mechanical apparatus, on which each change of circumstances 

 produces a direct, unvarying, inevitable effect. And yet it is on 

 record that such a frog, if kept alive long enough for the most 

 complete disappearance of the direct effects of the operation, will 

 bury itself in the earth at the approach of winter, and is able to 

 catch and swallow flies and other food coming in its neighbourhood, 

 although in other respects it shews no signs of an intelligent 

 volition, and answers with unerring mechanical certainty to the 

 play of stimuli. We may add that in some fishes the removal of 

 their cerebral hemispheres, which in these animals form a relatively 

 small part of the whole brain, produces exceedingly little change 

 in their general behaviour. 



These however are not the considerations on which we wish 

 here to dwell ; we have quoted the behaviour of the bird deprived 



