610 THE HUMAN BODY. 



possible by repeated operations, taking away only a part at 

 a time, to successfully remove almost all the surface gray matter 

 of the cerebral hemispheres from dogs ; and the animals have 

 recovered so as to perform many ordinary movements so well 

 that a person observing them only for a short time would 

 notice nothing abnormal. But in such cases not only some 

 cerebral cortex has been left but also the deeper lying corpora 

 striata and optic thalami: when these gray masses and all 

 the cerebral cortex are removed, as is possible in frogs and 

 birds, the animal does not move unless directly stimulated, 

 or so rarely that movements which appear due to a spontane- 

 ous volition are probably due to some unobserved irritation or 

 stimulation. In addition to loss of willed movements there 

 is loss or nearly complete loss of perception, that is, of the 

 power of mentally interpreting and giving a meaning to in- 

 coming nervous impulses. The pigeon or rat will start at a 

 loud noise, but makes no attempt to escape, as if it conceived 

 danger; it will follow a light with the eyes but make no at- 

 tempt to escape from a hand stretched out to seize it ; it can 

 and does swallow food placed in its mouth, but will starve if 

 left alone with plenty of it, the sight of edible things seeming 

 to arouse no idea or conception. It has been doubted whether 

 the animals have any true sensations; they start at sounds, 

 avoid opaque objects in their road, and cry when pinched; but 

 all these may be unconscious reflex acts : on the whole it seems 

 more probable, however, that they have sensations but not 

 perceptions ; they feel redness and blueness, hardness and soft- 

 ness, and so on; but sensations, as already pointed out, tell 

 in themselves nothing; they are but signs which have to be 

 mentally interpreted as indications of external objects or of 

 conditions of the Body: it is this interpreting power which 

 seems deficient in the animal deprived of its forebrain. In 

 some cases a like state appears to occur in man in connection 

 with abnormal states of parts of the cerebral hemispheres. 

 The patient may have eye, retina, optic nerves and all the 

 endings of these in the optic thalami and corpora quadrigemina 

 intact, and his pupils react to light, and the eyes follow a 

 bright object, yet the object arouses in the patient no idea as 

 to its nature : apparently he sees it, but he is mind blind. 



The Medulla Oblongata. Lying on the ventral aspect of 

 this (Chap. XII) on the sides of the continuation of the anterior 

 fissure of the cord are the two masses of nerve-fibres known 



