CEREBELLUM, PONS, AND MEDULLA. 241 



second, a loss of tone in the muscles of the limbs and trunk, par- 

 ticularly in the hind limbs, a condition of atonia; and, third, a 

 loss of steadiness in the muscular contractions, a condition of 

 astasia. The astasia manifests itself in a tremor of the muscles 

 when voluntarily contracted, especially in movements requiring 

 much exertion. Luciani supposes that this tremor is due to an 

 alteration that is, a slowing of the rhythm of discharges of the 

 impulses from the motor centers. The functions of the cerebellum 

 on his theory are expressed, therefore, by saying that it is an aug- 

 menting organ for the activity of the neuromuscular apparatus ; and 

 that, so far as this augmenting or strengthening activity can be ana- 

 lyzed, it consists in an increase in the energy of the motor discharges 

 (sthenic action), an increase in the tension or tone of the motor 

 centers and their connected muscles (tonic action), and an increase 

 in the rhythm of the motor impulses (static action) so that nor- 

 mally the muscular contractions are of the nature of complete 

 tetani. Luciani believes that this action of the cerebellum is 

 continuous, although varying in intensity, and that it affects all 

 of the musculature of the body, and not simply the muscles con- 

 cerned in body equilibrium. This constant motor activity is in 

 turn dependent upon a constant inflow of sensory impulses into 

 the cerebellum along its afferent connections, particularly upon the 

 impulses from the vestibular portion of the internal ear, and those 

 from the muscle sense fibers and similar fibers of so-called deep 

 sensibility. The constant augmenting activity of the cerebellum 

 is, therefore, a species of reflex effect, a reflex tonus which 

 affects all the musculature. Whether the cerebellar mechanism 

 is especially arranged to co-ordinate its effect upon the neuro- 

 muscular apparatus that is, in some way to adapt the move- 

 ments to a definite end Luciani leaves an open question. He 

 does not believe that a lack of co-ordination (cerebellar ataxia) 

 is necessarily present in cerebellar lesions; but admits that, if this 

 symptom is an invariable one, it would be necessary to add to 

 the general augmenting activity of the cerebellum also a general 

 adaptive or co-ordinating activity. It is precisely this latter feature 

 which stands out in the minds of most physiologists as the 

 characteristic function of the cerebellum, while Luciani considers 

 that it is not demonstrated by clinical or experimental facts, and 

 that even if demonstrated it would have to be considered as a 

 part perhaps a subordinate part of the functional influence of 

 this organ. 



Conclusions as to the General Functions of the Cerebel- 

 lum. It is evident that an authoritative statement of the function 

 or functions of the cerebellum is impossible. It seems quite clear, 

 however, that the organ exerts a regulating influence of some kind 

 16 



