342 THE BODY AT WORK 



removed retains all its natural enterprise, all its instincts, all 

 its emotions ; but every action which requires it to maintain its 

 centre of gravity in an unstable position gives it trouble. 

 Placed in water so that its body is supported, it swims almost as 

 well as a normal dog. It is, however, easy to lay too much 

 stress upon the balancing function of the cerebellum. The 

 disturbance of this function attracts our attention ; yet it is 

 probably but the indirect result of the suppression of activities 

 of a more widespread character. No animal ventures such 

 liberties with its centre of gravity as the biped Man ac- 

 complishes, without thinking, every time that he descends a 

 flight of stairs. Yet the cerebellum of the limbless whale, 

 that lives in a medium which decentralizes its gravity, so to 

 speak, bears the same proportional relation to the rest of the 

 nervous system as that of Man. Strangely enough, it is the 

 only cerebellum in the animal kingdom which so closely re- 

 sembles Man's that it might be passed off as belonging to a 

 human giant ; another reminder of the difficulty of deducing 

 the functions of the several parts of the organ from a study of 

 their relative development. What have a man and a whale 

 in common which determines the identity in form of their 

 cerebella ? How has it come about that two cerebra as widely 

 unlike as a man's and a whale's should be associated with a 

 common form of cerebellum ? 



If we apply to grey matter the distinction between sensory 

 and motor nerve-tissue having no exact terminology, it is 

 difficult to avoid these metaphorical expressions the cere- 

 bellum is essentially a sensory development. It grows from 

 the very margin of the infolding groove, which, when closed, 

 becomes the central canal of the brain and spinal cord, its 

 elements being marshalled in intimate association with sen- 

 sory root-fibres. Its millions of loops formed by the axons of 

 granules and the collecting processes of Purkinie-cells, are 

 by-paths which tap the conductors of sensory impulses. From 

 some those, for example, which originate in the muscles 

 and tendons, and in the semicircular canals more of the 

 impulse is diverted to the cerebellum, from others less. The 

 organ has no motor functions. It does not discharge neurones 

 which control skeletal muscles, or plain muscle, or glands. 

 Yet it influences the passage of impulses through sensori- 



