294 STUDIES IN LIFE AND SENSE. 



converted into a sensory impression ending in consciousness or 

 knowledge. Equally important is the question, how does the brain 

 regulate the direction and transmission of the messages innumerable 

 which hour by hour flit in and out of its portals ? To such a query 

 no answer is possible. Why or how we are able to move this finger 

 or that, how we can lift this limb or the other, is a mystery of mys- 

 teries in modern physiology, dwelling as yet in the farthest Arcanum 

 of the science. Lord Dundreary's question, " why a dog wags his 

 tail," if placed in contrast to his lordship's companion and equally 

 grave query, "why does the tail not waggle the dog?" in reality 

 involves a physiological enigma of which not even the shadow of a 

 reply is yet visible. All that may be said on this head is, that the 

 brain must possess amongst its other attributes the pointsman-like 

 power of directing nerve-impulses into whatever channels the will 

 and mind may prompt. Thus the physiological mystery of the will 

 is as deep and insoluble, at present, as the metaphysical or theological 

 aspects of the question ; and thus appears before us a puzzle ex- 

 ceeding that of the Sphinx in its gravity in plain language, we are 

 unable to tell the reason why we are able to do as we like. 



Summing up the few details we have gleaned in our elementary 

 but highly essential study of the broad mechanism of nerves and 

 brain, we may thus learn to distinguish between sensory and motor 

 impressions and between the nerve-fibres along which each is con- 

 veyed. We note the power of the brain to reflect, rearrange, and 

 transmit such impulses as reach its substance. We have seen that 

 reflex action in reality forms the basis of our own life and habits, and 

 by a further extension of thought we may note the part it plays in 

 the life of all other beings. When a snail's tentacle is touched, that 

 modest gasteropod withdraws itself from public observation, and 

 retires at once into the quietude of private life. Reflex action, which 

 has transmitted the sensation of touch to the nearest nerve-centre 

 and thence to the muscles of the body, is clearly responsible for the 

 behaviour of the mollusc. Even a sea-anemone captures the crab 

 that has stumbled against its tentacles by a like or allied exercise of 

 nerve-acts ; and the sensitive plant, and Venus' Flytrap, exhibit the 

 essential features of nerve action in that information received is 

 transmitted elsewhere through the organism, and reacts upon the life 

 and existence of the plant. 



For the due performance of reflex action three things are required. 

 First in point of importance comes a nerve-centre ; next in import- 

 ance we place a sensory, and then a motor nerve-fibre, leading respec- 

 tively to and from the nerve-centre. Concerning the nerve-centre we 

 have hitherto spoken as if the brain were the sole representative of the 

 chief office of the telegraphic system of the frame. Be it known, 

 however, that whilst the brain is such a centre, or rather collection 



