THE NEUROMUSCULAR MECHANISM 91 



as though it were necessarily integral in its nature, we may 

 be taking an unwarranted liberty. 1 The objection to 

 this view, that a muscle containing some active and some 

 idle elements should give evidence of the fact by its 

 general appearance, is not a weighty one. A muscle which 

 is maintained in a prolonged contraction probably pre- 

 sents an intricate picture of alternating activity among 

 its fibers. If we could distinguish what is going on we 

 might see hundreds of these shortening, while correspond- 

 ing numbers might be relaxing. The net result of rhyth- 

 mic action on the part of vast numbers of units, providing 

 that they keep "out of step," may well be to give a gross 

 impression of constant shortening. This is precisely the 

 explanation offered by Lingle 2 for the continuous or "tonic" 

 contraction observed in the alimentary canal. 



If we adopt the description of the muscular mechanism 

 given above, we can accept Lucas' theories entirely, and 

 shall assume that a small movement is one to produce 

 which only a small percentage of the available fibers are 

 put into simultaneous contraction, while a* large one is the 

 external sign of the more general participation of the 

 fibers. The experimenter sometimes sees indications of 

 localized responses in skeletal muscle, and more attention 

 to this matter is greatly to be desired. It is certain that 

 if there is any failure of the nerve-cells to act when a muscle 

 contraction is being sustained, there will be unemployed 

 fibers in the muscle. We readily grant that the power 

 developed by physical training is partly due to increased 

 ability to make groups of muscles act together, and it does 

 not seem unlikely that there is such a thing as an intra- 

 muscular coordination which has to be secured. 



Many interesting considerations follow the admission 

 that muscles may act fractionally. It becomes quite pos- 

 sible that a part of the resources represented may not be 

 within reach of our usual deliberate control. Such inac- 



1 Gertrude F. Barbour and the author in American Physical 

 Education Review, February, 1912. 



2 American Journal of Physiology, 1910, xxxvi, 361. 



