448 PHYSIOLOGY CHAP. 



peculiar form of motor ataxy, which has been well described as 

 " drunken gait " a name which suggests itself at once to every 

 one who sees an animal attempt to walk for the first time after 

 removal of its cerebellum. A careful analysis of this reeling zig- 

 zag gait shows that it results from the same factors which we 

 distinguished in the gait of animals with a half-cerebellum, i.e. 

 from asthenia, atonia, and astasia, and from compensatory pro- 

 cesses, which are not, however, limited to one side, but involve 

 both. 



On the disappearance of the dynamic phenomena of the early 

 post-operative period, the dog remains for a certain time incapable 

 of standing on its feet and sustaining the weight of its own body. 

 At each attempt to get up it falls now on one side and now on 

 the other. Later it begins to rise on the fore-limbs only, because 

 the hind-limbs flex at each attempt to stand up. 



That this inability of the animal to assume and maintain the 

 upright posture is due solely to asthenia, atonia, and astasia, and 

 not to inability to co-ordinate its movements, nor to deficient 

 equilibrium, is proved by the fact that during this period the 

 animal is able to swim as well as any normal dog. 



At a later period the animal manages to rise gradually, and to 

 take a few steps, but it frequently falls to one side or the other, 

 owing to the flexion of the limbs, particularly the hind -legs, 

 which are always the weakest. In the upright position it is never 

 still for a moment, and always seeks the support of a wall in its 

 first attempts at walking. It is only later that it gradually learns 

 to walk without support and to fall less often and less suddenly, 

 till at last it avoids this altogether. 



This functional restitution is only to a minimal extent due to 

 organic compensation ; it depends fundamentally upon functional 

 compensation. We must carefully examine the form and the 

 effects of these compensatory processes, because it is these that 

 give its most characteristic feature to cerebellar ataxy. 



These compensatory processes consist mainly in exaggerated 

 abduction of the four limbs in walking. This widens the base of 

 support and lowers the animal's centre of gravity, making it less 

 liable to fall ; at the same time the swaying of the body increases, 

 as this is a reaction to the resistance which its feet encounter from 

 the ground (Fig. 79, p. 119). 



The decerebellated animal cannot use the muscles of the 

 vertebral column to compensate its symptoms, as they are atonic 

 and asthenic on both sides ; this contributes to the horizontal 

 oscillations and frequent alternating displacements of the animal's 

 centre of gravity to right and left. The not uncommon cross- 

 ing of the fore-limbs, so that the right foot is set down to the 

 left and the left foot to the right side, is undoubtedly a com- 

 pensatory adaptation, intended to obviate the effects of these 



