CEREBRAL LOCALIZATION 217 



1. Ataxia. — This, one of the most constant signs, 

 is easily detected if the patient is able to walk. 

 When he is in bed, it may be brought out by making 

 him try to pronate and supinate rapidly for a minute 

 or two ; or to make and unmake a fist quickly, over 

 and over again. This sign is the more convincing 

 if it is unilateral. 



2. Atonia is very variable ; the knee-jerks may 

 be absent, normal, or excessive, and may change 

 day by day. 



Thiele and others have proved that the great 

 increase of tone noticed in man or animals after 

 lesions involving the pyramidal and other long 

 descending tracts depends on the integrity of Deiter's 

 nucleus. This lies just at the junction of the pons 

 and medulla, beneath the outer part of the floor of 

 the fourth ventricle, and therefore in close relation 

 to the cerebellum. If it is destroyed, or if it is cut 

 off from influencing the spinal cord by a complete 

 transverse division below Deiter's nucleus, the 

 spasticity and increased reflexes which ordinarily 

 follow lesions of the motor paths will fail to develop. 



Some cerebellar abscesses and tumours press on 

 the pyramids (above their decussation) but not on 

 Deiter's nucleus. These cause increase of tone on 

 the opposite side. Others destroy Deiter's nucleus, 

 and cause loss of tone on the same side. Others do 

 not involve either, and tone may be normal, or a 

 little increased on the same side as the lesion. 



3. Asthenia may be evidenced by weakening of the 

 grip, tendency to fall, or drooping of the head on the 

 affected side. It is not very constant. 



