vin THE HIND-BRAIN 437 



early post-operative period are associated with a form of vertigo, 

 and that they are neither the converse to, nor an exaggeration of, 

 the defect phenomena of the second post-operative period, because 

 they are not fundamentally due to excessive activity nor to 

 paralysis of the cerebellum. 



The explanation of the dynamic phenomena of the first period 

 is still a mystery; it is very doubtful how far they depend on 

 irritation or paralysis of the cerebellar peduncles. It is incon- 

 testable, and in our opinion clearly proved, that it is impossible 

 at present to argue from these phenomena in regard to the normal 

 functions of the cerebellum. If in our 1891 Monograph all 

 these dynamic phenomena of the early post-operative period were 

 referred on the strength of ablation experiments to irritation, on 

 the other hand we avoided the more serious error of assuming 

 them to be the converse of the true phenomena of cerebellar 

 deficiency. Indeed, we have repeatedly noted that phenomena of 

 irritation prevail in the muscles of the fore-limbs and neck, and 

 phenomena of deficiency in the muscles of the hind-limbs and 

 vertebral column. 



IV. As the dynamic phenomena of the first period disappear, 

 the symptoms which depend on loss of the cerebellar functions 

 become more and more prominent. These, as we have already 

 said, constitute the syndrome which is known as cerebellar ataxy. 



The dog, after removal of half its cerebellum and as the early 

 dynamic phenomena are disappearing, is so weak in the muscles 

 of the limbs on the operated side, particularly the hind-limbs, 

 that at first sight they appear paralysed. In order to move from 

 one place to any other, it is obliged to crawl on the buttock of 

 the operated side, the principal effort being made with the muscles 

 of the healthy side. This inability to stand upright and walk 

 may last four weeks. During this time, however, if the animal 

 can lean the flank of the operated side against a wall, it is able 

 to stand upright and make regular steps. Further, if thrown 

 into water, it keeps itself quite well on the surface, maintains 

 its equilibrium, and swims with perfect co-ordination. But if 

 its method of swimming be carefully watched, it is seen that it 

 cannot keep the trunk perfectly horizontal, but the operated side 

 lies constantly deeper in the water than the normal side. More- 

 over, the animal is unable to swim in a straight line, and 

 constantly makes circus movements to the sound side. 



The interpretation of these facts is obvious. The animal is 

 incapable of standing on its feet and walking unless it can find 

 support on the operated side, because the weakness of the limbs 

 on that side is so great that they cannot bear the weight of its 

 body. It succeeds in swimming well, because the water supports 

 the weight of the body. In swimming, its healthy side is higher, 

 and it continually turns towards this side, because the move- 



