124 ANATOMY AND PHYSIOLOGY 



Massage is beneficial in conditions of nerve-muscle tire, because 

 it improves the circulation while the patient is in a passive state, 

 so that better nutrition is secured and accumulated waste re- 

 moved, without the necessity for effort by the patient. (The 

 same is true of bruises and sprains.) No bad results will follow 

 moderate overuse, provided sufficient rest be promptly secured. 

 The expression "a healthy tire" is a logical one, because by 

 reasonable use a muscle grows, if suitable resting time is secured. 

 Beyond a reasonable limit, however, overuse is injurious; the 

 muscles work irregularly, perhaps painfully; nutrition declines; 

 wastes accumulate, and the will is no longer in control. Writer's 

 cramp is a familiar example. 



,The various stations and postures of the body are made 

 possible by properly adjusted muscle groups, which enable us to 

 preserve our balance in different positions. It is here that the 

 extensibility and elasticity of muscle tissue are of greatest impor- 

 tance. Sitting and standing, as well as walking and running, 

 are states of activity, whereby the flexor and extensor muscles 

 (and associated groups) oppose each other in equilibrium. It is 

 truly "hard work to keep still." 



The activities of muscles and nerves are so closely associated 

 that they cannot be well understood apart, and will be further 

 studied in Chapters XX and XXI. 



Rigor Mortis. It is already stated that muscle fibers are 

 composed of muscle cells ; the cell consists of muscle plasma 

 encased in a delicate substance called sarcolemma. The plasma 

 contains minute fibrils and various nutrient substances, mostly 

 proteins (page 153). Upon the death of the body coagulation of 

 muscle plasma occurs and certain proteins are separated from the 

 plasma in the form of a clot. (Myosin and Myogen fibrins.) 

 This coagulation results in a firm contraction of the muscle fibers, 

 and a general rigidity, called rigor mortis. It appears first in the 

 muscles of the lower jaw, and, advancing downward, gradually 

 involves the upper extremities and the whole body. 



In the case of chronic disease, or of defective blood supply, 

 the rigor appears soon (it may be as early as fifteen minutes) and 

 passes soon. After an acute disease it appears late and lasts longer. 



The disappearance of rigor mortis is due to the formation of 

 acids in the muscle fiber, which soften the fiber. 



