906 THE CEREBELLUM. 



the lesion occur early before the mechanisms of the nervous system 

 have lost in some degree their pristine elasticity, and if sufficient 

 length of time be then allowed them, injury to the cerebellum, even 

 though large, can be to an extraordinary extent compensated, and its 

 evil overcome. Man with one-half of his cerebellum congenitally gone 

 can pass muster among his fellows as normal both in mind and body. 

 Such adaptive compensation is as striking as the instances that occur 

 in animals after removal of portions of the cerebral hemisphere 1 or 

 removal of the otic labyrinth. 2 Luciani's searching investigations have 

 indicated that it is in the crossed hemisphere of the cerebrum itself that 

 this compensatory mechanism must be looked for, at least in major 

 part. 



The second step toward interpretation of the cerebellum is already 

 partly prejudiced in the procedure toward the first. The main fact 

 available from the study of the structure of the organ is its extra- 

 ordinarily rich connection with afferent nerves. The main phenomena 

 displayed by cerebellar excitation and destruction are, on the other hand, 

 not sensory but motor in kind. The action of the cerebellum must lie, 

 therefore, somewhere within this gap. 



A notion tacitly admitted above, in dealing with the disturbances 

 ensuing on cerebellar lesion, supposes that ablation is followed by 

 " irritative " signs at first, and then by signs of pure defect. Luciani 

 has dealt with the discrimination between the two. He finds 

 the former accentuated when the lesion involves the peduncles. It 

 must be remembered that a peduncular lesion is the exact kind of 

 injury which breaks the greatest number of paths with the least 

 mechanical disturbance. If I take his meaning rightly, its argument is 

 as follows. The cerebellum is an organ acting in a tonic and trophic 

 way upon the sensori-motor (Eolandic) sphere of the cortex cerebri and 

 on other parts. An immediate accompaniment of a mechanical lesion 

 of the cerebellum is excitement of the organ in the vicinity of the lesion. 

 This affects organs influenced by cerebellar activity, the effect simulating 

 increased cerebellar action. This " irritative " effect of the lesion lasts, 

 maintained by chemical and mechanical changes at the seat of injury, 

 for a considerable time, some days at least. To it succeeds a period in 

 which the excitation due to irritation having subsided, the results of 

 deficient action of the cerebellum lie unmasked. There appear to me 

 objections to this view. (1) The symptoms ascribed to irritation are 

 hardly sufficiently the converse of those of defect, e.g., the spastic extension 

 and abduction of limb characteristic of the first stage might on this 

 hypothesis be expected to give way to marked flexion and abduction in 

 the second. (2) The immediate though almost momentarily transient 

 effect of severing a peduncle is the production of an attitude truly the 

 converse of that which very quickly later, on completion of the sever- 

 ance, ensues in permanence. 3 It would be useful to know what is the 

 movement elicited by electrical excitation of the peduncles. If the 

 attitude be the converse of that produced by ablation, the explanation 

 of the latter cannot well be irritative. Terrier's excitations of cortex 



1 Goltz, "Die Vorrichtungen des Grosshirns," Arch. f. d. ges. Physiol., Bonn, 1876, 

 Bd. xiii., onwards. 



2 Cyon, ibid., 1874, Bd. viii.; E\vald,zWa., 1887, Bd. xli.; 1889, Bd. xliv., and "Physiol. 

 Untersuch. ueber d. Endorgan d. N. octavus," "Wiesbaden, 1892. 



3 For instance, see Budge, " Lehrbuch d. speziel. Physiol. d. Menschen," 8te Aufl., 

 Leipzig, 1862 ; Lussana, loc. cit. 



