76 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



voluntary innervation more and more difficult, and the fatigue 

 itseK, we have good reason for believing, develops in the motor end- 

 plate and in the nerve centers more quickly than in the muscles, 

 and this arrangement serves, therefore, to protect or safeguard the 

 muscle from an extreme condition of fatigue. 



While strain, as usually seen, may not be carried far enough to 

 injure the muscle itself beyond the possibilities of restoration, there 

 is evidence from the occupational neuroses that the nerve centers 

 may be damaged, and there is evidence also that other mechanisms, 

 such as the heart and blood-vessels, may be injuriously affected, 

 particularly if any abnormalities in structure or function are al- 

 ready present. Strain as defined above is an ahnost necessary 

 accompaniment of some athletic contests, particularly so-called 

 track athletics, in which the competition is such that the individual 

 is called upon to exert his utmost strength. Long distance running 

 matches and similar contests may have some value in the training 

 of individuals for special tasks, but certainly they cannot be con- 

 sidered as hygienic forms of exercise. 



