394 ^ PHYSIOLOGY 



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 recognition of the persons that fed it, nor any signs of pleasure or 

 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. 



With the development of the cerebral hemispheres in the higher mammals 

 there is a considerable shifting of motor reactions from those which are 

 immediate and ' fatal ' or inevitable to those which are educatable. The 

 cerebral hemispheres in man take a large part in the determining of even 

 the common reactions of everyday life. Ablation of the hemispheres 

 therefore, or even part of the hemispheres, in the ape and man gives rise 

 to much more lasting symptoms than is the case in the animals we have just 

 studied. These defects we shall have to consider more fully later. The 

 results however obtained on the lower animals, from the dog downwunU. 

 -how that the brain stem, from the head ganglion of the optic thalamus back 

 to the medulla, with the BpinaTcbrd, represents a complex mechanism which 

 can be played upon by impulses received through all the sensory apparatus 

 of the body, and is able to adjust the motor and visceral reactions to the 

 immediate environment of the animal. 



Certain of these immediate reactions are susceptible of further physiologi- 

 cal analysis. We have seen that the spinal cord contains the co-ordinated 

 mechanism for the movement of the limbs. We may now discuss how the 

 movements of the limbs are >-nr<liiiat<>(l with tlios.> of the trunk and head in 

 the maintenance of the unstable position of the animal in standing and in 

 locomotion. For this purpi.M- tin-re has been developed the great mass of 

 nerve matter in the roof of the metencephalon, viz. the cerebellum. 



