CEREBELLUM, PONS, AND MEDULLA. 237 



Interpretation of the Experimental and Clinical Results. — 



Flourens was led by the striking results of his operations on pigeons 

 to suggest the view that the cerebellum is an organ for the co- 

 ordination of the movements of equilibrium and locomotion. 

 Objections were raised to this view. Some observers (Dalton, 

 Weir Mitchell) found that if the pigeons from which the cerebeUum 

 had been removed were kept long enough the effects first observed 

 gradually disappeared, so that finally the animals were able to 

 move or fly with no marked difference from the normal animal 

 except that fatigue was shown much more quickly. Hence the 

 view advocated by Mitchell that the essential function of the 

 cerebellum is that of an augmenting apparatus for the voluntary 

 movements. With regard to this view it may be remarked in 

 passing that pigeons with the cerebral hemispheres removed exhibit 

 apparently as a permanent symptom the same tendency to rapid 

 fatigue after sustained muscular effort. By the same logical process 

 therefore one might conclude that one function of the cerebrum 

 is that of an augmenting organ to the motor discharges from the 

 cerebellum or midbrain. So also the cases of complete or nearly 

 complete atrophy of the cerebellum in human beings in which no 

 evil result follows other than a slight degree of cerebellar ataxia 

 have been used as an argument against the view that this organ 

 is necessary to the co-ordination of the complex voluntary move- 

 ments. The view that the cerebellum has essentially a direct 

 co-ordinating function has been criticized most seriously by Luciani. 

 This observer made a series of long-continued and most careful 

 observations upon dogs and monkeys in which the entire cere- 

 bellum or certain definite parts had been removed. He lays stress 

 upon the fact that the violent disturbance of movement is tem- 

 porary and is slowly recovered from in time. He was led, therefore, 

 to view these disturbances as due primarily not to the loss of the nor- 

 mal functional activity of the organ, but to irritations resulting from 

 the operation. When this stage of irritation is passed the real 

 defects which indicate the true function of the cerebellum become 

 apparent. These defects exhibit themselves as a loss of power 

 in the neuromuscular apparatus of the complex voluntary move- 

 ments, and he analyzes these results under three heads: First, 

 a loss of force in the muscular contractions, — a condition of asthenia ; 

 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 slowmg — of the rhythm of discharges of the 

 impulses from the motor centers. The functions of the cerebellum 



