I I'll I TS OP l M'l Rl MENTAL l.i 310 841 



very largely dm tin- sense of smell, we find thai d rebration caus< ani- 

 mal i" become completely immobile. It can nut seek f 1 I" the 



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

 stroyed. In a bony fish, mi the other hand, decerebration '•,-. 

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

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

 able l<> distinguish edible from nonedible material. 



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

 thalami have been simultaneously removed. Even when 3tructu 



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

 very Little different from the uormal frog. It sprint away when toucl 



it (-limits 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 May to the same kind of stimulus. 

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

 to he occasionally observed. Such a frog is said indeed to read 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 he 

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

 bird is more active than usual during daylight, hut 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 ,; 

 bration becomes \^vy difficult. Goltz, however, succeeded some >• 

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

 ing the operation in three stages separated by considerable intervals 



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



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

 reilexes were perfectly normal. It could not distinguish objects, hut a 

 brigh.1 light caused it to close its eyes. During daytime it walked 

 tinuously up and down its 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. Then 

 absolutely no signs ,,f pleasure or of recognition of the person that 

 it or of fear. 



