THE NERVOUS SYSTEM 447 



directions. Their spread, as judged by the effects, increases 

 with increase of stimulation of the radiant path, but the 

 irradiation remains limited to certain lines. Under weak 

 stimulation these lines are few. The conducting network affords, 

 therefore, to any given path entering it, some communications 

 that are easier than others. This is sometimes expressed, bor- 

 rowing electrical terminology, by saying that the conductive net- 

 work from any given point offers less resistance along certain 

 circuits than along others. This recognises the fact that the 

 conducting paths in the great central organ are arranged in a 

 particular pattern. This pattern of arrangement of the conduct- 

 ing network of the central organ reveals something of the inte- 

 grative function of the nervous system. It tells us what organs 

 work together in true relationship. The impulses are led to this 

 and that effector organ, gland, or muscle, in accordance with 

 the pattern. 



The receptive neurone forms, as we have seen, the sole avenue 

 by which impulses generated at its receptive point can be con- 

 veyed to their destination. It is a path exclusive to the impulses 

 generated at its own receptive points, and other receptive points 

 than its own cannot employ it. The receptive neurone forms a 

 private path exclusively devoted to impulses from a single recep- 

 tive point. Our study of the skin will have shown that its entire 

 surface is a collection of receptive points. On reaching the cord 

 the impulses pass along certain association'tmcts or internancial 

 paths — i.e., paths which connect the various segments of the 

 cord. These are paths common to groups of private paths, and 

 at their termination the impulses pass from their synapses across 

 the space which separates them from the first link or neurone 

 in the chain of the efferent path. The efferent path passes out 

 in the case of the cord, by the inferior spinal nerves to the gland 

 or muscle concerned, where it terminates in a final neurone. 

 The motor or efferent path differs in one important respect from 

 the sensory or afferent, inasmuch as it is not exclusively devoted 

 to the transmission of impulses generated at one single receptive 

 source alone, but receives impulses from many receptive sources 

 situated in various regions of the body. It is the sole path by 

 which all impulses, no matter whence they come, must travel if 

 they would reach the muscle, gland, etc., concerned. It is a 

 public path common to impulses of all kinds, such as tissues are 

 constantly receiving. Reflex arcs arising, therefore, in different 

 sense-organs can pour their influence into one and the same 

 muscle. A limb-muscle is the terminus ad quern of nervous arcs 

 arising not only in the right eye, but in the left ; not only in the 

 eyes, but in the organs of smell and hearing ; not only in these, 

 but in the otic labyrinth, in the skin, and in the muscles and joints 



