262 DETAILED SYNTHESIS. 



physician to good health ; they give beauty to the grace- 

 ful, and may be a mine of wealth to all, that princes can- 

 not buy nor untold riches equal.* 



SECTION in. 



Nerves. 



594. It IS VERY EASY TO UNDERSTAND the Structure, 



general arrangement, and purpose' of the nerves, but 

 precisely how they perform their duties is one of the 

 mysteries of life from which the curtain has not yet 

 been lifted. 



595. NERVES ARE either white or reddish gray 

 pulpy cords, about the consistence of new-made cheese, 

 of various sizes, extending either between nervous cen- 

 tres, when they are called commissures, or between a 

 nervous centre and some other part of the Body. 



596. NERVES LARGE ENOUGH TO BE SEEN WITH THE 

 NAKED EYE are bundles, covered by a thin sinewy 

 sheath. Hence a nerve readily splits up into delicate 

 fibres. 



597. NERVOUS FIBRES ARE CONSTRUCTED of fibril- 

 lae, having three parts, an outer envelope or sheath nu- 

 cleated like basement membrane, inclosing a layer of oily 

 substance, called the Medullary sheath, in the centre of 



* The author has not thought it necessary in this work to speak of any 

 particular calisthenic or gymnastic exercises, since there are so many good 

 works upon those subjects. The classes of motion are few, and may be 

 traced by the divisions or classes of muscles laid down. Any kind of ex- 

 ercise that brings into action all the muscles gracefully (and that is best 

 done under the influence of music), without great exertion, and excites 

 active respiration, is sufficient, while exercises that cause the " holding of 

 the breath," or those thaj put a person " out of breath," are not advisable. 

 Indeed, the chief benefit of any exercise is derived from its causing in- 

 creased respiration. Therefore, muscular exercise, to be advantageous, 

 must be taken in pure air, and with the chest perfectly free to move. 



Foot-note. What not necessary ? What sufficient? 594. What ? 695. What 

 597. How-? 



