xvi THE NERVOUS SYSTEM 309 



The brain of the frog is in one respect a favorable object 

 for the study of function, inasmuch as large parts of it may 

 be removed without causing the death of the animal. The 

 shock effects following operations are much less in cold- 

 blooded animals than in birds and mammals ; the subjects 

 recover more quickly, and will endure the removal of much 

 larger portions of the brain. But even in the frog the after- 

 effects of certain operations wear off very slowly. There is 

 danger in removing parts of the brain, of attributing results 

 to the loss of the part in question, which may be due to 

 injuries produced by the operation. The behavior of the 

 animal some months after being operated upon is often quite 

 different from its behavior before complete recovery. For 

 this reason different investigators of the functions of the 

 frog's brain have arrived at contradictory results. It is only 

 after waiting until the shock effects of the removal of a part 

 of the brain have completely worn away, that we can arrive 

 at a correct idea of the normal role of that part in the life of 

 the animal. 



Cerebral Hemispheres. - - It is frequently stated that a 

 frog which has lost its cerebral hemispheres loses nearly all 

 its spontaneity ; that it remains sitting in one position for 

 an indefinite time, if not disturbed ; and that it takes no food 

 unless it is forced into its mouth. While it is still able 

 to hop and swim, avoid obstacles placed in its path, and 

 perform many other movements in an apparently normal 

 manner, it is said to lose the power of originating actions 

 independently of outer stimuli. The experiments of Schra- 

 der showed the incorrectness of these commonly accepted 

 conclusions. The symptoms so frequently ascribed to loss 

 of the cerebral hemispheres are those which follow when a 

 part of the thalamencephalon is also removed or subjected 

 to severe injury. Schrader found that if the cerebral hemi- 



