viii THE HIND-BRAIN 443 



When the bitch that had lost the right half of its cerebellum 

 was held up by its flanks in the air, the muscles of the right hind- 

 limb were seen to be more relaxed than those of the opposite side, 

 as in the hind -leg of Brondegeest's frog, after section of the 

 posterior spinal roots. On lifting the soles of the animal's feet 

 with the palm of the hand, greater resistance to passive flexion 

 was felt in the leg of the healthy side than on the side operated 

 on ; the latter, indeed, could be flexed beyond the normal limit, 

 that is, farther than the limb of the sound side. If the animal 

 was watched while feeding in the upright position, with its limbs 

 separated to widen the base of support and its whole attention 

 given to its food, it was noticed repeatedly that the legs of the 

 injured side gradually gave way, so that the animal would have 

 lost its equilibrium and fallen to this side, if it had not become 

 aware of its danger in time to recover its equilibrium by suitable 

 compensatory movements. 



The tendency of the animal to fall towards the operated side 

 during the early days after removal of one-half of the cerebellum 

 is evidently related to the passive flexion of the limbs when 

 it is intent on its food. On watching carefully, it is evident 

 that the fall is due, not to the irregular position of the injured 

 limbs, but to the unexpected relaxation of the muscles, which the 

 animal has not yet learned to guard against. 



Another more easily observed phenomenon may in our opinion 

 be referred to the too sudden relaxation that follows the contraction 

 of the muscles, owing to diminution of their tone. We noticed in 

 our bitch that the limbs of the operated side were lifted higher 

 than the normal, as if she had to mount up little steps, and 

 that she set them down more forcibly on the ground, and thus 

 made more noise on the wooden floor. It appears to us highly 

 probable that the abnormal elevation is the effect of the too rapid 

 relaxation of the extensors of the limbs during the contraction of 

 the flexors, and the stamp the effect of the too rapid relaxation of 

 the flexors while the extensors contract. We shall return to this 

 phenomenon in order to discuss other and less probable interpreta- 

 tions of it. 



To this group of symptoms, which are intimately connected 

 with and yet distinct from asthenia, we gave the name of atonia, 

 which has met with general acceptance. 



A third group of symptoms may be added to asthenia and 

 atonia if the mode in which the contractions are carried out is 

 carefully observed. In normal limbs the contractions of the 

 muscles are gradual and sustained in character, that is without 

 interruption of continuity, without trembling or oscillation, and 

 with perfect fusion of their elementary impulses. When lying 

 down in its kennel the animal, after removal of half its cerebellum, 

 only differs from the normal animal by a slight and almost con- 



