Human Phy oology, i?7 



brain; but how a very soft tube, filled with a milky fluid, can 

 carry sensations of heat, cold, form, texture, pleasure, or pain, 

 or how the brain can convert them into ideas of bodies, passes 

 all comprehension. It is one of the mysteries of life. No more 

 can we understand how the mind, through the medium of the 

 brain, can play upon all the muscles of the body as an organist, 

 pressing upon white and black keys, plays upon all the pipes of 

 an organ. Another nervous action is also required. We must 

 not only be able to contract a muscle, but to know how much 

 it is contracted to feel, and so limit and regulate, the action we 

 produce. This may be a modified action of the nerves of sen- 

 sation, and how nice this must be those know who have tried 

 to walk on a rope or perform the more difficult feats of balanc- 

 ing and the lighter gymnastics. 



In the complex nervous and muscular operations of speak- 

 ing and singing, a great number of muscles are brought into 

 action, and the nervous control of the small muscles of the 

 glottis and vocal chords is so rapid and accurate as to enable 

 singers to perform all the wonders of a cultivated vocalization r 

 md the mocking-bird to imitate all the birds of the forest, and 

 all sorts of sounds beside, with unerring accuracy. And what 

 are we to think of the composition and action of the nerves 

 that carry to the brain and the mind every fine modulation of 

 sound, quality of tone, intensity, pitch, and every shade of 

 emotion or passion which the tones convey? What of the action 

 of the optic nerve which conveys instantaneously the impres- 

 sions of form, colour, light, shade, motion of the myriads of 

 objects in a varied landscape? What of the sensitiveness of 

 some olfactory nerves which distinguish all the scents of the 

 gardens, kitchens, people, and animals of a large area? The 

 shepherd's dog can pick out his master's sheep from other 

 flocks ; he can track his master, or even his master's horse ; he 

 knows the scent of every person and animal of his acquaintance. 



In the distribution of the nerves of animal life, belonging to 



M 



