SPECIAL PHYSIOLOGY OF MUSCLES. 61 



This low tone is inaudible, from the small number of vibrations a 

 second. 



Muscle Fatigue. Prolonged or excessive muscular activity is 

 followed by a diminution in the power of producing work and by an 

 increase in the duration of the muscular contractions. Fatigue is 

 accompanied by a feeling of stiffness, soreness, and lassitude, refer- 

 able to the muscles themselves. In the early stages of muscular 

 fatigue the contractions increase in height and duration, to be fol- 

 lowed by a progressive decrease in height, but an increase in dura- 

 tion, until the muscle becomes exhausted. The cause of the fatigue 

 is the production and accumulation of decomposition products, such 

 as phosphoric acid and phosphate of potassium, CO 2 , etc. A fatigued 

 muscle is rapidly restored by the injection of arterial blood. 



Work Done. Muscles are machines capable of doing a certain 

 amount of work, by which is meant the raising of a weight against 

 gravity or the overcoming of some resistance. The work done is calcu- 

 lated by multiplying the weight by the distance through which it is 

 raised. Thus, if a muscle shortens four millimeters and raises 

 250 grams, it does work equal to 1,000 milligram-meters, or one 

 gram-meter. If a muscle contracts without being weighted, no work 

 is done. Equally, when the muscle is over-weighted so that it is 

 unable to contract, no work it done. The amount of work a muscle 

 can do will depend upon the area of its transverse section, the length 

 of its fibers, and the amount of the weight. The amount of work 

 a laborer of 70 kilograms weight performs in eight hours averages 

 105,605 kilogram-meters, or 340.2 foot-tons. 



. SPECIAL PHYSIOLOGY OF MUSCLES. 



The individual muscles of the axial and appendicular portions of 

 the body are named with reference to their shape, action, structure, 

 etc. e. g., deltoid, flexor, penniform, etc. In different localities a 

 group of muscles having a common function is named in accordance 

 with the kind of motion it produces or gives rise to e. g., groups 

 of muscles which alternately behd or straighten a joint, or alter- 

 nately diminish or increase the angular distance between two bones, 

 are known respectively as flexors and extensors ; such muscle groups 

 are in association with ginglymus joints. Muscles which turn the 



