THE NERVOUS SYSTEM 341 



Clarke " on the median side of the posterior horn. Further 

 than this we cannot go. We are ignorant of the nature of the 

 sensory impressions collected by the cells of Clarke. The 

 cerebellum also receives through its middle peduncle the 

 axons of cells which lie in the pons Varolii on the opposite 

 side ; which cells are discharged by impulses descending from 

 the cortex of the great brain. It is not improbable that it 

 gives to the great brain as many fibres as it receives from it. 



If we had no experimental evidence as to the part which the 

 cerebellum plays in the harmonious working of the whole 

 nervous system, we should infer from its structure and con- 

 nections that it is somewhat mechanical, a co-ordinator of the 

 activities of other parts rather than in itself a functionally 

 independent organ. Pathological and physiological observa- 

 tions very definitely justify this conclusion. They show that 

 the cerebellum is not essential to life. It may be completely 

 destroyed by disease or removed by operation without robbing 

 the individual of any single function or capacity. Disease of the 

 cerebellum does not diminish the patient's sensitiveness to 

 every kind of stimulus, nor does it deprive him of the use of 

 any single muscle ; but it reduces him to the condition of a 

 person who in gait, but not in mind, is habitually drunk. 

 When he walks he staggers from side to side ; when he 

 stretches out his hand it trembles. His movements are jerky ; 

 his head shakes, his eyes oscillate ; he suffers from a feeling of 

 giddiness ; his speech comes haltingly. Cerebellar ataxia, 

 which is a rare disease, resembles in many respects the much 

 commoner " locomotor ataxia " produced by disease of the 

 spinal ganglia and the parts of the cord connected with pos- 

 terior roots ; but careful analysis of the symptoms shows that 

 they are due, not to want of the sensations which guide move- 

 ments, but to inability to regulate the force of muscular con- 

 tractions. A man suffering from locomotor ataxia falls when 

 he closes his eyes, because, not being able to feel with his feet, 

 he is dependent upon vision for information as to his attitude. 

 When the cerebellum is diseased, the patient is no less unsteady 

 with his eyes open than he is with them closed. 



The results of cerebellar disease or injury bring home to us 

 the fact that a nice adjustment of movements is needed to main- 

 tain equilibrium. A dog from which the cerebellum has been 



