THE REFLEX ACTIONS OF THE SPINAL CORD. 571 



tracting muscles to the central nervous system, and guiding the discharge 

 of the efferent impulses which call forth the contractions. When these 

 afferent impulses affect consciousness we speak of them as constituting a 

 " muscular sense ; " it is, as we shall see, by the " muscular sense" that we 

 become aware of and can appreciate the condition of our muscles. But we 

 have reason to think that the afferent impulses which constitute the basis of 

 the muscular sense, whatever be their exact nature, in order to play their 

 part in bringing about the coordination of a voluntary movement need not 

 pass right up to the brain and develop a distinct muscular "sense," but may 

 produce their effect by working on the nervous mechanisms of the spinal 

 cord with which the motor fibres carrying out the movement are connected. 

 In other words, the coordination of a voluntary movement takes place in 

 the part of the spinal cord which carries out the movement, and not in the 

 brain, though the latter may be conscious of the whole movement including 

 its coordination. 



But if the spinal cord possesses mechanisms for carrying out coordinated 

 movements, which in the case of voluntary movements are discharged by 

 nervous impulses descending from the brain, we may infer that in reflex 

 actions the same mechanisms are brought into action though they are dis- 

 charged by afferent impulses coming along afferent nerves instead of by 

 impulses descending from the brain. The movements of reflex origin, in all 

 their features except their exciting cause, appear identical with voluntary 

 movements ; the two can only be distinguished from each other by a know- 

 ledge of the exciting cause. And it seems unreasonable to suppose that the 

 spinal cord should possess two sets of mechanisms in all respects identical, 

 save that the one is discharged by volitional impulses from the brain and the 

 other by afferent impulses from afferent nerves. 



We are led therefore to the conclusion that in a reflex action two kinds 

 of afferent impulses are concerned : the ordinary afferent impulses which dis- 

 charge the nervous mechanism within the cord and so provoke the move- 

 ment, and the afferent impulses which connect that nervous mechanism with 

 the muscles about to be called into play, and which take part in the coordi- 

 nation of the movement provoked. The nature of these latter afferent im- 

 pulses is at present obscure ; but if we admit, as we seem compelled to do, that 

 the character of a reflex action is determined by them as well as by the affer- 

 ent impulses which actually discharge the mechanism, it seems possible that 

 a fuller knowledge of these coordinating afferent impulses may afford an 

 adequate explanation of the fact that when, as in the case of the frog in 

 question, the usual set of muscles cannot be employed by the nervous 

 mechanism, recourse is had to another. 



We have avoided the introduction of the word " consciousness " as un- 

 necessarily complicating the question ; and it would be out of place to discuss 

 psychological problems here. We may remark, however, that since we have 

 no objective proofs of consciousness outside ourselves, and only infer by 

 analogy that such and such an act is an outcome of consciousness on account 

 of its likeness to acts which are the outcome of our own consciousness, we 

 conclude that the brainless frog possesses no active consciousness like our 

 own, because absence of spontaneous movements seems to be irreconcilable 

 with the existence of an active consciousness whose very essence is a series 

 of changes. Consciousness, as we recognize it, seems to be necessarily ope- 

 rating as, or to be indissolubly associated with the presence of, an incessantly 

 repeated internal stimulus ; and we cannot conceive of that stimulus failing 

 to excite mechanisms of movement which, as in the case of the brainless 

 frog, are confessedly present. We may, however, distinguish between an 

 active continuous consciousness, such as we usually understand by the term, 



