MENTAL PHYSIOL G Y. 



109 



later, and who announced to the Royal Society 

 his conversion in a paper on " Scolopendra" 

 which was printed in the " Philosophical Transac- 

 tions." Notwithstanding the proof of priority 

 thus afforded, and notwithstanding that Prof. 

 Owen, before Mr. Newport's paper had been 

 read, had announced his own acceptance of Dr. 

 Carpenter's doctrine, and had given Dr. Carpen- 

 ter full credit for having originated it, some Con- 

 tinental writers have assigned the honor of the 

 discovery to Newport. The evidence is so clear 

 that the point is not worth discussing, but it is 

 mentioned in order to show for how long a period 

 Dr. Carpenter has occupied a prominent place 

 among the philosphers who have made a special 

 study of the functions of the nervous system. 

 Returning from this digression, it is to be ob- 

 served that the Articulata possess not only a 

 chain of centres of reflex action, usually one for 

 each segment of the body, with afferent and ef- 

 ferent nerves which are mainly subservient to 

 the movements of the legs, but that they also 

 possess organs of sense, notably large and well- 

 developed eyes, from which afferent nerves pro- 

 ceed to special ganglia. These differ from the 

 ganglia of the cord in this, that the central 

 change produced in them by an impression made 

 upon their afferent nerves is attended by sensa- 

 tion. The efferent nerves from the optic ganglia, 

 or some of them at least, pass down the cord to 

 its own simple reflex, or "motor" ganglia, and 

 exert either a " motor" or a controlling influence 

 upon them ; but the effects which are thus pro- 

 duced, although attended by sensation, may be 

 just as purely " reflex" or automatic, as entirely 

 dissociated from any idea of the purposes which 

 they fulfill, as those which are produced directly 

 by the motor ganglia themselves. When a centi- 

 pede is running along the ground its progression 

 is reflex only. The successive contacts of its 

 feet with the surface send impressions along the 

 afferent nerves to the motor ganglion of each 

 segment, and these impressions produce changes 

 in the ganglia which cause motor impulses to be 

 sent along the efferent nerves to call the muscles 

 of the legs into action. If a visible obstacle is 

 placed in the insect's path, as soon as this is 

 seen — that is to say, as soon as the impression 

 made upon the afferent nerves of the eyes has 

 been communicated to the optic ganglia — the 

 resulting change is conveyed by their efferent 

 nerves all along the axial cord, or chain of motor 

 ganglia, and first arrests, and then modifies, the 

 motion of the legs The insect will first stop, as 

 if to reconnoitre the obstacle, and will then turn 



away, as if to avoid it. If the axial cord is com- 

 pletely cut through in two places, the movements 

 of progression will be unaffected, but the power 

 of the sense of sight to arrest motion will only 

 extend as far as the first place of division. When 

 the obstacle is seen, the legs of the anterior third 

 of the body will stop moving, but those of the 

 posterior two-thirds will continue their move- 

 ment, and will push the anterior third along. If 

 the motor ganglia between the two places of di- 

 vision are destroyed, the legs of the middle seg- 

 ments will be paralyzed, and will cease moving ; 

 but those of the anterior and posterior segments 

 will carry the middle ones along. When an ob- 

 stacle is seen, the legs attached to the anterior 

 segments will stop ; those attached to the pos- 

 terior segments will continue their progression ; 

 and the middle segment, the legs of which are 

 paralyzed, will be doubled up between the other 

 two. In the higher animals and in man the 

 spinal cord is surmounted by several pairs of 

 sensory ganglia, which collectively form what is 

 called the sensorium, and which are subservient 

 not only to the " five " senses of sight, smell, 

 hearing, taste, and touch, but also, in all proba- 

 bility, to every variety of consciousness, even to 

 the consciousness of the intellectual operations. 

 It is believed that the brain thinks, as the eye 

 sees, without the production of consciousness 

 until the thought-change has been conveyed to 

 the sensorium. 



Pausing for a moment upon the two great 

 nerve-functions which have been mentioned, re- 

 flex motion and sensation, it is found that they 

 produce or govern a very considerable proportion 

 of the vital actions of man. Perhaps the best 

 example of a purely reflex action is the sucking 

 of a newly-born infant, which is excited by the 

 contact of any soft substance with its lips ; and 

 the ordinary movements of the chest in bi'eathing 

 are of the same character. The presence of ve- 

 nous blood in the lungs produces an impression 

 upon afferent nerves which proceed to the respira- 

 tory ganglionic centre, and the resulting change 

 in that centre directs a wave of motor impulse 

 along the efferent nerves which proceed to the 

 muscles by which the chest is moved. But in 

 man, and probably also in the higher animals, the 

 change produced in the motor ganglion is not 

 limited to the motor channel of discharge, but 

 also passes upward to the sensorium and excites 

 sensation, so that the original impression is felt. 

 This is more especially true when the impression 

 itself is of unusual intensity. For example, we are 

 ordinarily unconscious of the impression which 



