EFFECTS OF EXPERIMENTAL LESIONS 841 



very largely on the sense of smell, we find that decerebration causes the ani- 

 mal to become completely immobile. It can not seek food because the 

 sense of smell, upon which it ordinarily solely depends, has been de- 

 stroyed. In a bony fish, on the other hand, decerebration causes very 

 little difference in the behavior of the animal, provided the thalami 

 and optic lobes have been left intact. It continually swims about and is 

 able to distinguish edible from iionedible material. 



In the frog the result depends very largely upon whether the optic 

 thalami have been simultaneously removed. Even when these structures 

 have been removed along with the cerebrum, the animal at first appears 

 very little different from the normal frog. It springs away when touched, 

 it climbs up an inclined plane, and when thrown in water it swims. It 

 is, however, quite incapable of producing any spontaneous movement, 

 and is in short nothing more than an extremely complex machine, re- 

 acting always in exactly the same way to the same kind of stimulus. 

 When the optic thalami are also intact, spontaneous movements are said 

 to be occasionally observed. Such a frog is said indeed to react on the 

 approach of winter as normal frogs do by preparing itself for hiberna- 

 tion, and with spring, to resume its activity and feed itself by catching 

 insects. 



In the bird, in which the operation of removing the cerebral hemi- 

 spheres is a very easy one, the movements after decerebration may be 

 quite complicated, particularly if the optic lobes are intact. Such a 

 bird is more active than usual during daylight, but becomes perfectly 

 still in the dark. It is, however, unable to distinguish friends from ene- 

 mies, and it shows no fear. 



As we ascend further in the animal scale, the operation of decere- 

 bration becomes very difficult. Goltz, however, succeeded some years 

 ago in removing practically all of the cerebrum from a dog by perform- 

 ing the operation in three stages separated by considerable intervals of 

 time. The animal lived eighteen months after the last operation, and 

 during this time it behaved exactly like an automatic machine. All its 

 reflexes were perfectly normal. It could not -distinguish objects, but a 

 bright light caused it to close its eyes. During daytime it walked con- 

 tinuously up and down its cage, whereas at night it would sleep and 

 remain perfectly quiet. When food was placed in the mouth, the dog 

 would masticate and swallow in a perfectly normal fashion, and would 

 reject unpalatable food. While asleep, a very loud sound might awaken it, 

 and when a harmful stimulus was applied to the skin, the animal would 

 snarl and growl and attempt to fight the offending object. There were 

 absolutely no signs of pleasure or of recognition of the person that fed 

 it or of fear. 



