THE SPINAL CORD AND CEREBELLUM 123 



inclined to overlook its consequences. Yet it is 

 undoubtedly a fact that our nervous system must be 

 fashioned so as to conform to this variability, which 

 is, as it were, the pivot on which it turns ; and were it 

 possible to create and build up a complicated organism 

 like our own, it would be incomplete, and it would 

 not function properly unless full and satisfactory pro- 

 vision were made for the sudden and forcible trans- 

 ference of its activity now into one part and now into 

 another. Within certain limits, the more powerful 

 such transference is, the more intense, one may say, 

 will the vital force of the organism be. 



As long as breath comes and goes in the body, even The 



nervous 



in a state of the most perfect repose, the whole may factors in 

 be said to be undergoing a process of oxidation ; but augmenta- 

 when passing from the condition of rest certain parts activity 

 become functionally active, oxidation in them is or^^gm. 

 rendered very much more intense. In this sudden 

 augmentation of activity three nervous factors come 

 into play. The first of these is of a sensory, or, it 

 may be, of a sensory-motor, nature (sensation leading 

 to motion) ; the second is a vaso-motor one ; the third, 

 intermediate between the other two, an increase of 

 impulse factor. Both pyschologists and physiologists 

 agree that the sensory factor is always the primary 

 one. You cannot will a sensation until you feel it ; 

 you cannot intensify the action of cells representing a 

 feeling or a thought until they have begun to vibrate. 

 Sensory impulses vary very much in the degree of 

 their intensity. We may hear a deafening crash, as 



