468 PHYSIOLOGY CHAP. 



resistance of the medium in which it flies or swims ; it does not 

 recognise the impenetrability of the objects which obstruct its 

 course ; it does not feel the weight of the body it has to carry ; this 

 is the physiological explanation of the disturbance of voluntary 

 movement described by Flourens. ' Le cervelet,' says this author, 

 ' est le siege exclusif du principe qui co-ordonne les mouvements 

 de locomotion.' The true function of the cerebellum, in short, is 

 the muscular sense." 



Undoubtedly Lussana's theory is an ingenious completion 

 and development of that of Flourens, save for his assumption 

 that the cerebellum is not the seat of any sensation. His hypo- 

 thesis is so lucid that it might find general acceptance were 

 not one thing direct experimental evidence for it lacking. 

 As a matter of fact, the occurrence of the staggering and reeling- 

 gait, and other locomotor disorder in decerebellated animals or 

 in diseases of the cerebellum is not enough to establish loss or 

 disturbance of muscular sense, because the normal regularity of 

 the movements does not depend exclusively upon the muscle sense. 



In 1903 a pupil of Munk Lewaudowsky again assumed 

 the cerebellum to be the centre for muscular sense, and claimed 

 that the phenomena of cerebellar ataxy consist in disorders of 

 co-ordination. 



As we have already given definite proof that both in animals 

 after removal of the cerebellum and in disease of this organ in 

 man the muscular sense is not in any way altered, it is 

 unnecessary to discuss this hypothesis again. But the position 

 taken up by Lewandowsky may detain us for a moment. 



He agrees that the generic term ataxy does not express a 

 unitary concept, but is simply a complex represented by certain 

 disorders of movements, or motor paralysis. " If," he adds, " a 

 definite concept were attached to the term ataxy, there would 

 be no ground for dispute as to what is meant by cerebellar ataxy." 

 Again, when we say that the animal or man whose cerebellum 

 is affected has an uncertain, reeling, swaying gait, similar to that 

 of a drunkard, we express, not a single phenomenon, but a 

 complex, which may be split into a number of components. 



What are the simple components of cerebellar ataxy for 

 Lewandowsky ? He verih'es the occurrence of astasia, atonia, 

 and neuro- muscular asthenia, which we have described and 

 demonstrated in various ways. He recognises the atonia by the 

 fact that the limbs of decerebellated animals can be flexed or 

 extended not only more readily than, but also beyond the range 

 of, the normal. He also describes asthenia, but does not admit 

 that it is due to defect of the stkenic action of the cerebellum. 

 He assumes that the complex movements only appear less 

 energetic because the synergic and co-ordinated actions of all 

 the muscles that come into play in the various voluntary move- 



