Eeceptoes, Neukons, and Effectors 123 



the cerebral cortex), down the spinal cord, and out through the spinal 

 root to the muscle. The afferent current from the visual mechanism is 

 not, however, distributed solely to the muscular apparatus involved di- 

 rectly in the production of the specific reaction prescribed in the instruc- 

 tions. The irritation spreads to other neurons, chains going to other 

 effectors, as, for example, to the extrinsic and intrinsic muscles of the eye 

 itself, to the heart, etc. The optic tract neurons from retina to mid-brain, 

 in other words, are the common beginning of a great many diverging arcs. 

 Conversely the discharge to the arm is not derived solely from the visual 

 apparatus, but is derived from a number of sources not definitely anal- 

 yzed ; the efferent neurons in this chain, that is, are simultaneously excited 

 from many different directions, and one such chain represents or com- 

 bines in itself the efferent terminal divisions of a large number of arcs. 

 It is the action of these arcs other than the dominating one — other than 

 the arc from eye to arm muscle — which brings about by the preliminary 

 arcs caused by the instructions and corresponding to the intention to react, 

 the formation of the dominant reflex-arc. 



REFLEX DOMINANCE. 



We are now in a position to consider the question of consciousness 

 from the point of view of the dominance of reflexes. The retinal arc in 

 the case above described may be said to dominate the total system in the 

 sense that for the time it is the central line of discharge, in regard to 

 which all other lines are derivatives or contributory. All the afferent 

 channels are, for the moment, secondary in their effects, and all the efferent 

 channels are subordinated to the demands of the dominating one. 



The condition of dominance and subordination is probably typical of 

 the reflexes which condition perceptual consciousness. In such cases 

 the discharge through the pathway from the sense organ affected domi- 

 nates the nervous system. The visceral discharges are in general less af- 

 fected than the somatic by such dominance, but in cases where there is a 

 strong emotional factor, as when a fearful or pleasing object is per- 

 ceived, there must be a considerable disturbance of the visceral efferent 

 system. 



The essential condition of attentive consciousness seems to be the func- 

 tioning of the nervous system as a whole. We have no reason to assume 

 that any reflex takes place without consciousness of some sort. If the 

 functions of the system were diffused — no arc dominating — there might 

 theoretically still be consciousness, but it would be absolutely inattentive; 

 of zero vividness. If the afferent, associative, and efferent neurons con- 

 stituting a single arc, or a large group of arcs, could be split off from the 



