CORRELATION OF REFLEXES. 551 



the effector organ in question. Before finally converging upon the 

 motor neurone arcs usually converge to some degree by their private 

 paths embouching upon internuncial paths common in various degree 

 to groups of private paths. The terminal path may, to distinguish it 

 from internuncial common paths, be called the final common path. 

 The motor nerve to a muscle is a collection of such final common paths. 



Certain results flow from this arrangement. One seems the pre- 

 clusion of qualitative differences between nerve-impulses arising in 

 different afferent nerves. If two conductors have a tract in common, 

 there can hardly be qualitative difference between their modes of con- 

 duction. 



A second result is that each receptor being independent for com- 

 munication with its effector organ upon a path not exclusively its own, 

 but common to it with certain other receptors, that nexus necessitates 

 successive and not simultaneous use of the common path by various 

 receptors using it to different effect. 



The first link of each reflex chain is a neurone which starts in a 

 receptor organ, e. g., a sense-organ. A receptive field, e. g., an area 

 of skin, is always analyzable into receptive points, and the initial nerve- 

 path in every reflex arc starts from a receptive point or points. A 

 single receptive point may play reflexly upon quite a number of differ- 

 ent effector organs. It may be connected through its reflex path with 

 many muscles and glands in various parts. Yet all its reflex arcs 

 spring from the one single shank, so to say; that is, from the one 

 afferent neurone that conducts from the receptive point at the periph- 

 ery into the central nervous organ. This neurone dips at its deep end 

 into the great central nervous organ, the cord or brain. There it 

 enters a vast network of conductive paths. In this network it forms 

 manifold connections. So numerous are its potential connections 

 there, that, as shown by the general convulsions induced under strych- 

 nia-poisoning, its impulses can discharge practically every muscle and 

 effector organ in the body. Yet under normal circumstances the im- 

 pulses conducted by it to this central network do not irradiate there 

 in all directions. Though their spread over the conducting network 

 does, as judged by the effects, increase with increase of stimulation of 

 the entrant path, the irradiation remains limited to certain lines. 

 Under weak stimulation of the entrant path these lines are sparse. 

 The conductive network affords, therefore, to any given path entering 

 it some communications that are easier than others. This canaliza- 

 tion of the network in certain directions from each entrant point is 

 sometimes expressed, borrowing electrical terminology, by saying that 

 the conductive network from any given point offers less resistance along 

 certain circuits than along others. This recognizes the fact that the 

 conducting paths in the great central organ are arranged in a particu- 



