612 PHYSIOLOGY OF THE BRAIN-STEM 



this increase of tonus would be of no use if the point of insertion of these mus- 

 cles were not fixed, hence there must be also an increase in the tonus of the 

 trunk muscles on the opposite side. The cerebellum exercises this regulating 

 influence by means of the various pathways proceeding from it to the motor 

 nuclei in the spinal cord and to the motor cortex in the cerebrum (cf. Fig. 271). 



It is likely that the compensation which gradually appears after extensive 

 injury to the cerebellum is the work of the cerebrum, particularly of the 

 motor regions (cf. Chapter XXIV). The following observations by Luciani 

 speak for such an explanation: 



Three operations were performed on the same dog: in the first the right 

 half of the cerebellum was removed; in the second the motor regions of the cor- 

 tex were destroyed in both cerebral hemispheres ; and in the third the remainder 

 of the cerebellum was taken away. The animal remained alive for eleven months 

 after the operation and was then killed. During these eleven months he could 

 neither hold himself up nor walk without support. In none of the animals 

 observed by Luciani in which the cerebellum alone was destroyed, did anything 

 like this occur. The difference was due, as Luciani observes, not to the mere 

 extirpation of the cerebral cortex, for this operation of itself produces only 

 transitory symptoms. It appears rather that destruction of the motor cortex 

 removed just those conditions which made it possible for the animal without a 

 cerebellum to find the necessary compensatory movements. It is especially 

 worthy of remark that swimming movements, which do not require to be coordi- 

 nated so finely as walking movements, could be performed by this animal per- 

 fectly well. 



The motor disturbances which appear immediately after the operation on 

 the cerebellum, the peduncles, or the pons are particularly severe and should 

 be given special mention. The animal sometimes gets into certain attitudes 

 called, forced positions, which it seems unable to get out of, returning inevita- 

 bly to the same posture every time it is compelled to take another; or it 

 performs what are called forced movements, rolling over and over around the 

 long axis of the body, or running around in a circle like a circus animal, or 

 describing cranklike movements around its anterior end as a pivot in all 

 of these being quite unable to prevent the movement, or, to put it differently, 

 apparently striving all the while for a state of equilibrium which it is unable 

 to find. 



The motor disturbances appearing after unilateral extirpation of the cere- 

 bellum at their period of greatest intensity are : agitation, restlessness, of ttlmes 

 whining or groaning, curvature of the spine with concavity toward the oper- 

 ated side, accompanied by tonic extension of the anterior extremity of the 

 same side and spasmodic movements of the three other extremities; spiral 

 rotation of the head and neck toward the sound side accompanied by strabis- 

 mus and nystagmus of one side, and often by deviation of the eye on the 

 operated side inward and downward, of the other eye outward and up- 

 ward; a tendency to roll over about the long axis of the body in the direction 

 of the twisting and of the strabismus i. e., as seen from the back of the 

 animal, from the sound toward the injured side. 



Whether these phenomena are caused by the excessive irritation on the 

 cut side, or by the predominance of the sound side over the injured one, 



