724 WITHOUT CEKEBKAL HEMISPHERES. [BOOK in. 



is to say, movements not started by any obvious stimulus, may 

 occur after removal of the cerebral hemispheres. But the 

 movements so witnessed differ from those of an intact bird. 

 They are, it is true, varied; and the variations are in part 

 dependent on external circumstances, the bird being guided by 

 tactile, and, as we have said, visual sensations, or, to be more 

 exact, by impressions made upon the sensory nerves of the 

 skin and on the retina; but they do not shew the wide varia- 

 tions of voluntary movements. The bird for instance never 

 flies up from the ground, never spontaneously picks up corn, 

 and its aimless, monotonous, restless walks, resembling the con- 

 tinued 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 develop- 

 ments might be witnessed, and indeed cases are on record where 

 birds have been kept alive for months after the operation, and 

 have shewn spontaneous movements of a still more varied char- 

 acter than those just described ; but in such cases the removal 

 of the hemispheres has not been complete, portions of the ven- 

 tral regions being left behind; and, though a mere remnant 

 left around the optic thalami can hardly be regarded as a suffi- 

 cient 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 

 4 automatism,' differs from the spontaneity of the ' will ' in 

 degree rather than in kind. Looking at the matter from a 

 purely physiological point of view (the only one which lias a 

 right to be employed in these pages), the real difference between 

 an automatic act and a voluntary act is that the chain of phys- 

 iological events between the act and its physiological cause 

 is in the one case short and simple, in the other long and com- 

 plex. We have seen that a frog lacking its cerebral hemi- 

 spheres, viewed from one standpoint, 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 opera- 



