THE SPINAL CORD AND CEREBELLUM 155 



dilatation of the small arteries. If, therefore, the 

 reinforcing influence of the cerebellum be exercised 

 through the medium of chemical action, there is a 

 strong presumption in favour of the view that it 

 either contains chemico-sensory cells or is directly 

 connected with those cells and fibres in the cerebral 

 and spinal systems by which metabolism is governed. 

 That portion of the cerebellum which it seems most 

 natural to regard as the connecting-link in these 

 processes is the molecular and cortical layer, and the 

 fact that certain portions of it do correspond function- 

 ally to certain parts of the body gives support to this 

 supposition. 



Although the nervous system, as we have just seen, chemical 

 undoubtedly exercises a controlling and stimulating constant 

 influence on the processes of metabolism, yet the nervous '" 

 opinion is generally held that trophic nerves, the sole ^''*-"^^^- 

 function of which is to act in a nutritive capacity, do 

 not exist. This requires a moment's consideration. 

 On the one hand it would be difficult to extend the 

 functions of those fibres which govern the secretory 

 processes in the submaxillary gland, whilst on the 

 other hand a motor fibre to a muscle is not one whit 

 less a nerve of chemical action than a nerve, let us 

 say, to the intestines. Chemical change is, indeed, in 

 a greater or less degree implied in all physiological 

 action. The gland builds itself up and breaks down 

 under the influence of nervous action just as the 

 muscle does. Probably all nerves are to some extent, 

 and the great majority are to a very great extent, 



