AND PHYSIOLOGY. 



135 



directly across the fibers the gash at once opens very widely ; 

 or if a bone is broken and the ends allowed to slide by each 

 other, it is only by great force that they can be brought back 

 to their proper places. The value of this property is seen in 

 keeping the muscles in a state ready for action, as well as in 

 assisting the ligaments to keep the joints firmly together. 



265. Dependent on Vital Energy— Both of these charac- 

 teristics are dependent upon nervous or vital energy. For if 

 life be extinct, or the nerve proceeding to any muscle be cut 

 off, tonicity and irritability soon cease ; although they remain 

 for a longer time in the involuntary than the voluntary mus- 

 cles. As, for example, the heart of a sturgeon, after its re- 

 moval from the body, has been known not only to pulsate for 

 a short time, but even to keep up its action until its folds 

 fairly rustled from inherent dryness. 



266. Muscular Waste the Cause of Muscular Contrac- 

 tion. — But here the question meets us, What is this power that 

 passes through the nerves to each fibril, and how does it energize 

 the muscle ? Is it a fluid acting on the fibers in the same manner 

 that water acts upon the strands of a rope, or is it an impon- 

 derable agency, like electricity or heat, passing through the 

 nerve by polar attraction or conduction from particle to par- 

 ticle ? At present we must rest with the facts of muscular 

 movement, and perhaps we can never solve the mystery in 

 this world. The nature of what we vaguely denominate 

 nervous or vital force has never been determined. No mys- 

 tery in religion exceeds that of muscular movement. It how- 

 ever seems to be the case that muscular contraction is in a good 

 degree dependent on a due degree of arterialization of the 

 blood ; for if a muscle be placed in carbonic ac'd its irritability 

 soon ceases, while in oxygen it remains a long time after it is 

 removed from the body. A want of the proper amount of oxy- 



Of what use is this property? 265. Upon what do both myotility and tonicity depend ? 

 In which muscles do they remain the longest after death ? Instance the heart of the stur- 

 geon. 266. What is all we know of the power that produces this contraction ? 



