COINAGES OF THE BRAIN. 293 



the phenomena of touch, and let us endeavour to see how Bell's 

 observation supplies the demonstration of the reflex or duplex theory 

 of nervous acts. When the impression which resulted in your 

 touching the table flashed down the spinal cord from your brain, 

 it was a motor impulse. As such, its definite track lay along the 

 anterior part of the spinal cord. It left the cord by the front roots 

 of the nerve-trunk passing to the arm ; and travelled along these 

 anterior fibres which unite with the fibres of the hinder root to form 

 apparently a uniform and single-fibred nerve. Reaching the limb, 

 the motor impression arrived at its terminus, and discharged its 

 duty by bringing the muscular arrangements of arm and hand into 

 co-ordination, and thus bringing finger and table into contact. A 

 " sensation " was thus brought into existence, but this latter impres- 

 sion probably consisting of the transformed "motor" impulse 

 which the instant before had travelled down the limb passed 

 rapidly backwards to the brain as a sensory impression. Along the 

 second set of fibres in the nerves of the limb it was duly conveyed. 

 Arriving at the grand junction where the branch nerve from the arm 

 joined the main line of the spinal cord, the impression passed along 

 the hinder root of the nerve into the cord, and ascended to the 

 brain by the hinder part of the great nerve-tract. In the brain- 

 centre, the " sensation " gave rise to consciousness and knowledge ; 

 and thus " reflex action " becomes demonstrated as a veritable entity 

 and as the method whereby the complex machinery of body is brought 

 into harmonious relation with the still more intricate mechanism of 

 brain and mind. 



Next in order, and by way of close to these preliminary studies 

 in sensation, we should note that it is perfectly immaterial, in so far 

 as the universality of reflex action as the basis of nervous acts is 

 concerned, whether the original or primary impulse begins in the 

 brain as the result of thought, or arises directly from the outer world 

 itself; that is, it matters not whether the first impulse or sensation 

 be "motor" or "sensory" in its nature the same sequence essen- 

 tially follows the initiation of any nervous action. The "mouth 

 waters " at the sight of a dainty proportionately, in the experience 

 of most of us, as the chances of obtaining the desired morsel grow 

 few and far between. Here a sensory impulse has passed to the 

 brain through a nerve (the optic) which happens to be of purely sen- 

 sory kind. In the brain the sensation, or sensory impulse, has been 

 transformed into an afferent impulse termed "secretory" in this 

 instance, because it is reflected to the salivary glands of the mouth, 

 with the familiar result just detailed of causing them to secrete their 

 characteristic fluid. In this case the "sensory" impulse therefore 

 begins the reflex act ; whilst in the case of touching the table it is a 

 "motor" impulse which first leaves the brain, and which is soon 



