WITHOUT CEREBRAL HEMISPHERES. 641 



may here perhaps remark that all these facts seem to point to the conclu- 

 sion that what may be called mechanical spontaneity, sometimes spoken of 

 as " 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 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 physiological 

 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 

 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 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 neighborhood, although in other 

 respects it shows no signs of an intelligent volition, and answers with un- 

 erring mechanical certainty to the play of stimuli. We may add that in 

 some fishes the removal of their cerebral hemispheres, which in these ani- 

 mals form a relatively small part of the whole brain, produces exceedingly 

 little change in their general behavior. 



These, however, are not the considerations on which we wish here to 

 dwell ; we have quoted the behavior of the bird deprived of its cerebral 

 hemispheres mainly to show that in this warm-blooded animal, as in the 

 more lowly cold-blooded frog, the parts of the brain below or behind the 

 cerebral hemispheres constitute a nervous machinery by which all the ordi- 

 nary bodily movements may be carried out. The bird, like the frog, suffers 

 no paralysis when the cerebral hemispheres are removed ; on the contrary, 

 though its movements have not been studied so closely as those of the frog, 

 the bird without its cerebral hemispheres seems capable of executing at all 

 events all the ordinary bodily movements of a bird. And in the bird as in 

 the frog, the afferent impulses passing into the central nervous system, 

 whether they give rise to consciousness or not, play an important part not 

 only in originating but in guiding and coordinating the efferent impulses 

 which stir the muscles to contract, the coordination being effected partly in 

 the spinal cord, but largely and indeed chiefly in the parts of the brain 

 lying behind the cerebral hemispheres. It is further worthy of notice that 

 spontaneity of movement of the kind which we have described is much 

 more prominent in the more highly developed bird than in the more lowly 

 frog. The cerebral hemispheres are not the only part of the central nerv- 

 ous system which has undergone a greater development in the bird ; the 

 other parts of the brain have also acquired a far greater complexity than 

 in the frog. 



553. In the mammal the removal of the cerebral hemispheres is still 

 more difficult than in the bird ; the animal cannot be kept alive for more 

 than a few hours; but in some mammals it is possible to observe during 

 those few hours phenomena kindred to those witnessed in the bird 

 and in the frog. The rabbit or rat, from which the whole of both hemi- 

 spheres has been removed with the exception of the parts immediately 

 surrounding the optic thalami, can stand, run, and leap. Placed on its 

 side or back it at once regains its feet. Left alone it generally remains as 

 motionless and impassive as a statue, save now and then when a passing 

 impulse seems to stir it to a sudden but brief movement ; but sometimes it 

 seems subject to a more continued impulse to move, in which case death 

 usually follows very speedily. Such a rabbit will remain for minutes together 

 utterly heedless of a carrot or cabbage-leaf placed just before its nose, though 



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