802 THE CENTRAL NERVOUS SYSTEM 



system. The more complex the integration, the higher the intelligence 

 of the animal. 



Besides performing these functions the nerve cells serve as store- 

 houses for memory impressions, certain types of them being especially 

 adapted for this function. The differences observed in the relative thick- 

 ness of the cell layers composing the cerebral cortex are more or less 

 associated with the function which it can be shown the different areas 

 of this possess. Nerve cells are extraordinarily sensitive to deficiency 

 in oxygen supply, and yet little evidence of oxygen consumption by 

 the brain can be revealed by the usual methods of investigation (page 

 396). 



THE INTERMEDIATE OR INTERNUNCIAL NEURON 



It would be profitless at this stage to consider the possible influences 

 that the intermediate neuron may have on the impulses passing along 

 the reflex arc. Before doing so we must see how the problem can be 

 approached, for it is plain that the neuron in the case of the simpler 

 reflexes is too short to make any investigation of its peculiar functions 

 a possibility. We must study the characteristics of some type of re- 

 flex in which this neuron is drawn out, such as the scratch reflex, in 

 which, as we shall see, it extends from the shoulder area of the cord 

 to the lumbar region. 



