THE STUDY OF MUSCLE PHYSIOLOGY. 20T 



increments of the weight. When oy^rstretched, muscle does 

 not return to its original length (loss of elasticity), hence the 

 serious nature of sprains. 



It is important to regard muscular elasticity as an expression 

 of vital properties. 



The work done by a muscle is ascertained by multiplying 

 the load lifted by the height ; and the capacity of an individual 

 muscle will vary with its length, the arrangement of its fibers, 

 and the area of its cross-section (i. e., the number of fibers). 



The work done may be regarded as a function of the resist- 

 ance (load), as the contraction is also a function of the stimulus. 

 The separation of a muscle from its nerve by section of the lat- 

 ter leads to certain changes, most rapid in the nerve, which 

 show that the two are so related that prolonged independent 

 vitality of the muscle is impossible, and make it highly proba- 

 ble that muscle is constantly receiving some beneficial stimulus 

 from nerve, which is exalted and manifest when contraction 

 takes place. 



The study of the development of the electrical cells of cer- 

 tain fishes shows that they are greatly modified muscles in 

 which contractility, etc., has been exchanged for a very decided 

 exaltation of electrical properties. It is likely, though not 

 demonstrated, that all forms of protoplasm undergo electrical 

 changes — that these, in fact, like chemical phenomena, are vital 

 constants. 



The phases of the contraction of smooth muscular tissue are 



all of longer duration; the con traction- wave passes in different 



directions, and may spread into cells devoid of nerves, which 



' we think not unlikely also to be the case, though less so, for all 



forms of muscle. 



The smooth muscle-cell must be regarded as a more primi- 

 tive, less specialized, form of tissue. Variations in all the phe- 

 nomena of muscle with the animal and the circumstances are 

 clear and impressive. Finally, muscle illustrates an evolution 

 of structure and function, and the law of rhjrthm. 



