NERVOUS SYSTEM IN GENERAL. 267 



If a marble be rolled about by the two fingers thus crossed, 

 it seems to be two. Here we use judgment with the sen- 

 sation. Ordinarily, we could not feel, at the same time, 

 one simple solid object with the outside of the first and the 

 inside of the second finger. This illustrates how we are 

 constantly using our judgment in interpreting our sen- 

 sations. We see few things as they are in themselves. 

 We see nearly everything in the light of past experiences. 



Lingering Effect of Sensations. We have noted the lingering 

 effects of sensations, how sights and sounds linger and are fused one 

 with the other. So we get continuous light from a series of flashes 

 if they follow each other in sufficiently rapid succession, and continu- 

 ous sound from a series of sounds that would be heard separately if 

 they are more than about a sixteenth of a second apart. So with 

 touch, if the finger be held against the teeth of a revolving wheel, if 

 the wheel revolve slowly, the touch of each tooth may be felt, but when 

 it whirls more rapidly the sensation becomes that of continuous pres- 

 sure. Experience and experiment both go to show that probably 

 nothing is wholly forgotten. Whatever acts upon a cell of nervous 

 matter makes its mark. It may become dim, but it is never completely 

 obliterated. The testimony of persons rescued from drowning, and other 

 similar experiences, goes to show that the record was yet in the mind. 

 We may fail to recollect, but we ever remember. 



Habits are Acquired Reflex Actions. The work of 

 the spinal cord is that of a subordinate officer, whose duty 

 is to relieve his superior, the brain, of many small tasks, 

 and to afford him relief from having all the details con- 

 stantly on his mind. If we learn to do many things me- 

 chanically, we save the effort of doing them by conscious 

 effort and act of will. Whatever we do for the first time 

 requires careful attention. To learn any new muscular 

 action, such as a new step in marching, fingering a musical 

 instrument, or typewriting, requires effort; they produce 

 more or less fatigue. Subsequent effort in doing the same 



