VIII 



THE HIND-BRAIN 471 



centrifugal, between the brain and the peripheral organs of sensa- 

 tion and motion ; 



(b) That it has no field of action of its own, i.e. belonging to 

 itself exclusively, which is not equally at the service of other 

 centres of the cerebrospinal system ; 



(c) That it is not a sensory centre properly so called, as the 

 sensory impressions which reach it by special afferent paths arouse 

 no conscious sensations, but normally remain subliminal, below 

 the threshold of consciousness ; 



(d) That under the special conditions in which its activity is 

 concerned, it may be regarded as a small coadjutant system to 

 reinforce the great cerebrospinal system. 



In agreement with the recent morphological and phylogenetic 

 investigations of Bolk, there is ample physiological demonstration 

 that the cerebellum is a single unpaired organ, each portion of 

 which has the same function as the whole. In fact the loss of 

 the vermis may be repaired, i.e. organically compensated, by the 

 lateral lobes, and after various cerebellar lesions, symmetrical 

 or asymmetrical, circumscribed or diffuse, the phenomena of 

 deficiency differ not in their nature and character, but solely in 

 intensity, extent, and duration, and by their more or less marked 

 influence on the muscles of one or other side of the body*. Our 

 own investigations proved clearly and decisively that unilateral 

 mutilations have a predominantly homolateral effect, i.e. much 

 more marked on the muscles of the same side, and not only on the 

 muscles that subserve posture and locomotion, but on all the 

 voluntary muscles and in particular on the muscles of the lower 

 or posterior limbs, and on frhe muscles that fix the vertebral 

 column. 



If the principal effects of cerebellar deficiency consist in atonia, 

 asthenia, and astasia, it follows logically that the coadjutant or 

 reinforcing influence that the cerebellum normally exerts upon the 

 rest f the system consists in a tonic, sthenic, and static neuro- 

 muscular effect by which 



(a) The degree of tension at which the neuro-muscular organs 

 remain during functional pause or rest is increased (tonic action) ; 



(b) The energy developed during the various voluntary, auto- 

 matic, and reflex actions is increased (sthenic action) ; 



(c) The rhythm of the elementary impulses of which these acts 

 are made up is accelerated, and their normal fusion and regulnr 

 continuity is maintained (static action). 



If it be once allowed that dysmetria of movement is a constant 

 phenomenon of cerebellar deficiency ; if, as Lewandowsky has 

 maintained, dysmetria is one of its essential and necessary phenomena, 

 and not a simple result of atonia or astasia, then we must add a 

 fourth factor. The tonic, sthenic, static effects must be supple- 

 mented by an adaptive action, on which the range, precision, and 



