EXPERIMENTAL STUDIES ON THE THALAMUS 27 



The brain stem was imbedded in celloidin and serial sections 

 cut of the entire preparation. These were stained with iron- 

 hematoxylin. 



The medulla oblongata and cerebellum showed no alteration, 

 judged by this method of staining. 



The midbrain and optic lobes showed no alteration except for 

 a small pocket of unstained vacuolated tissue on the left side at 

 the anterior end. The posterior commissure and oculomotor 

 nerves are intact and stained in a normal way. 



All of the optic thalamus is gone except the hypothalamus and 

 the posterior end of the right side of the thalamus. The anterior 

 commissure is gone. The line of excision runs from the poste- 

 rior commissure above to the anterior surface of the optic chiasma 

 in a slightly oblique frontal plane so as to slightly damage the 

 left optic lobe and leave part of the posterior end of the right 

 thalamus. 



DISCUSSION 



The points of major interest in the preceding protocol may be 

 summarized as follows: 



1. A nearly complete removal of the thalamus destroys the 

 temperature regulating mechanism of the pigeon so that its body 

 temperature is determined by that of the environment. 



2. As the body temperature fluctuates, the behavior and reflex 

 activities also vary. 



3. If the body temperature is kept normal, the behavior of the 

 bird resembles that of a decerebrate bird without thalamic 

 injury in the following respects: 



a. Periodic spontaneous walking movements occur, particu- 

 larly during periods of food deprivation. 



b. The maintenance of body equilibrium remains normal. 



c. The feathers may assume a fluffed condition that resembles 

 that of the decerebrate bird, but is never as marked as in the 

 latter. 



d. Complicated spinal reflexes involving the coordinated move- 

 ment of the beak to the toes are carried on efficiently. 



