THE FUNCTIONS OF THE BRAIN STEM 445 



According to Schrader and Steiner, if care be taken not to injure 

 the optic thalami, spontaneous movements may be occasionally 

 observed after removal of the cerebral hemispheres. On the approach 

 of winter such a frog has been observed to bury itself in order to hiber- 

 nate, and with spring to resume activity and to feed itself by catching 

 insects. The .behaviour of such decerebrate animals depends on the 

 part taken in the initiation of movement and adapted reactions by 

 stimuli entering through the higher sense-organs. Thus an ordinary 

 bony fish after ablation of the cerebral hemispheres maintains its normal 

 equilibrium in water. It is continually swimming about, stopping only 

 when it reaches the side of the vessel or when worn out by fatigue. 

 Here, again, if the thalami and optic lobes be intact the fish has been 

 observed to show very little difference from a normal animal and to 

 possess the power of distinguishing edible from non-edible material. 

 On the other hand, in the elasmobranch fishes, which depend mainly 

 upon their olfactory apparatus as a guide to movement, the removal 

 of the cerebral hemispheres with the olfactory lobes, or of the latter 

 alone, produces complete immobility and absence of spontaneous 

 movement, even though the optic thalami and optic lobes may be 

 intact. 



In the bird the cerebral hemispheres may be removed with ease. 

 A decerebrate pigeon, if its optic lobes be intact, walks about avoiding 

 all obstacles, and may even fly a short distance. In the dark, i.e. in 

 the absence of visual impressions, it remains perfectly still. The bird, 

 however, is unable to recognise food, or enemies, or individuals of the 

 opposite sex ; it shows no fear and responds to stimuli like the brainless 

 frog described above. 



Goltz has succeeded in the dog in removing the whole of the cerebral 

 hemispheres in three operations. The dog was kept alive for eighteen 

 months after the final operation. It was able to walk in normal 

 fashion and spent the greater part of the day in walking up and 

 down its cage. At night it would sleep and then required a loud 

 sound to awaken it. It reacted to stimuli in a normal fashion, shutting 

 its eyes when exposed to a strong light, shaking its ears in response to a 

 loud sound. On pinching its skin it attempted to get away, snarling or 

 turning round and biting clumsily at the experimenter's hand. It 

 had no power to recognise food and had to be fed by placing food in its 

 mouth, though, if this food were mixed with a bitter substance, such 

 as quinine, it was at once rejected. The dog never showed any signs 

 of pleasure, or recognition of the persons that fed it, or of fear. 

 Removal of the hemispheres had thus produced loss of all understand- 

 ing and memory. There was no sign of conscious intelligence, and 

 all the actions of the animal must be regarded as reflex responses to 

 immediate excitation. 



