CHAPTER VI 



THE AFFERENT PART OF THE NERVOUS SYSTEM 



THE great majority of the fibers which bear impulses 

 toward the central stations have their receptive endings 

 near the surface of the body. A minority come from 

 localities deeply submerged and, therefore, subject to 

 stimulation as the result of internal rather than external 

 conditions. The function of all afferent fibers is to cooper- 

 ate in the production of reflex responses; a certain propor- 

 tion of them, in addition, carry to the gray matter the 

 impulses which determine sensation. With the shifting 

 of our attention we are continually consigning to the class 

 of reflex producers fibers which but must now furnished 

 us with the data of consciousness. Our interest in sen- 

 sation is so immediate and overwhelming that we tend 

 to underestimate the unobtrusive work of those afferent 

 elements which at any given moment are guiding sub- 

 conscious processes. 



Nerve-fibers of the Skin. The human skin has been 

 computed to have an area of about 1.7 square meters. 

 It is thus as large as a rug 3 feet wide and 5 feet long. 

 Afferent fibers in enormous numbers lead from small sub- 

 divisions of this large expanse and no point upon it is far 

 removed from nerve-terminals. Sherrington has attract- 

 ively compared the skin with its nerves to the surface 

 of a pond where many aquatic plants are growing. Their 

 branching filaments are distinct from one another, but 

 often overlapped or entwined. When a stone is thrown 

 into the pond it stirs most decisively the growth on which 

 it directly falls, but other leaves and stems will share 

 somewhat in the disturbance. Perhaps in some respects 

 the skin is even more like a marsh in which the foot sinks, 



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