

q 

a 1905.] Thalamus and Deiter’s Nucleus to Spinal Cord, etc. 361 
removed in slices the carotids were previously tied on both sides. The 
animals used were cats, dogs, and monkeys. | 
The following results were obtained :— 
A. Those Relating to Decerebrate Rigidity. 
It was found that rigidity did not commence till the section was made at 
the level of the posterior part of the optic thalamus. The rigidity thus 
obtained became more intense as the lesion was carried farther back in the 
mesencephalon. The rigidity lasted till the line of section passed through 
the trapezium. Directly the section passed behind the pons the rigidity 
disappeared, and did not return as long as the animal was kept alive. In 
some cases at this stage the animal assumed a general position of flexion for 
a short time. Gradual removal of the cerebellum was found to be without 
influence in decerebrate rigidity when this had been previously produced, but 
immediately the lesion was carried through Deiter’s nucleus the rigidity was 
abolished. This abolition of the rigidity was homolateral. 
Similarly division of the Deiter spinal tract without any injury to the rest: 
of the cerebellum caused homolateral relaxation of decerebrate rigidity. In 
some cases, however, the’ relaxation was not complete, or it returned to a 
slight degree after a time. In such exceptional cases subsequent unilateral 
bulbar transection did not always abolish the persistent rigidity, which then 
must clearly be of spinal origin. An irritative lesion of Deiter’s nucleus or 
the tract caused a temporary Increase of the spasm. | 
When unilateral lesions were made in the mesencephalon the results 
varied with the position of the section. If the lesion was made immediately 
behind the thalamus, contralateral rigidity was by far the most marked; if 
farther back, the homolateral rigidity was most marked. 
Section of the afferent roots belonging to a limb caused the abolition of the 
decerebrate rigidity in that limb and prevented its occurrence when performed 
previous to the mesencephalic transection. Division of the posterior columns 
or of the direct cerebellar tracts, or of both, in no way interfered with the 
occurrence of decerebrate rigidity or caused its abolition. 
In all the experiments in which removal of the tentorium was required 
marked extensor rigidity exactly like that following mesencephalic transec- 
tion occurred. The same result was invariably obtained, but the more 
carefully the removal was accomplished the less marked was the rigidity. 
Bisection of the superior vermis without previous removal of the tentorium 
also produced a bilateral extensor rigidity exactly like decerebrate rigidity. 
Removal of one lateral half of the posterior part of the superior vermis 
also caused a bilateral extensor rigidity most marked homolaterally. 
VOL, LXXVI.—B. 2B 
