.">() THK NERVOUS SYSTEM AM) ITS CONSERVATION 



here the afferent filter- conveying a form of energy from 

 tin- outlying region to the central organ-, the resulting 

 release of fresh energy there, and the conveyance of the 

 returning impulses to the contractile tissues. We do not 

 now believe that the incoming and outgoing energies 

 dit'ter in any such qualitative fashion as Descartes sup- 

 posed, but we can recognize in his description the impor- 

 tant truth that the efferent flow is much more voluminous 

 than the afferent. If we consider typical cases we shall 

 come to appreciate the striking disproportion between the 

 two. 



1 ii:. 8. The afferent neuron influences directly four efferent neu- 

 rons. 



Take, for example, the wink which is caused by the 

 contact of a minute particle with the surface of the eye. 

 The area stimulated may be so Miiall that we can scarcely 

 think that more than a .-ingle nerve-filter is concerned 

 in the afferent transmission which follows. Yet to pro- 

 duce the imi.-ciilar response a very large number of fibers 

 must be made to bear impulses to the mu.-cles involved. 

 Perhaps the coughing reflex will serve our purpose even 

 better. Here an irritating particle hardly larger than 

 that required to cause the wink may act upon the central 



