TETANUS, CRAMP, FATIGUE 125 



MUSCLE TISSUE, A SOURCE OF HEAT AND ELECTRICITY 



Thus far we have considered only one result of muscle action ; 

 namely, the production of motion. Muscle tissue is built up of 

 food derived from the blood- contraction means a using up of its 

 substance, and the formation of waste products. These chemical 

 processes are going on continually, and all chemical action is ac- 

 companied by the production of heat. A muscle in action is there- 

 fore a machine for producing body heat, and since the muscular 

 system comprises so large a portion of the human body (weighing 

 nearly three times as much as the bones), it is one of the chief 

 sources of heat; for the double reason that it includes a great deal 

 of tissue, and that it is more constantly at work than any other 

 tissue in the body. 



We all know that the body temperature rises during muscular 

 exercise; as the vessels dilate, bringing oxygen for chemical action, 

 heat is rapidly evolved and waste is swept away. (Blood- and 

 lymph vessels carry both food and waste.) 



In addition to other results of muscle activity, a slight current 

 of electricity is produced, appreciable only by certain experiments. 



MODIFICATIONS OF MUSCLE ACTION 



Clinical notes. Tetanus is a condition of the muscles in which 

 the contractions are so rapid that the action appears to be con- 

 tinuous; the stimuli come so rapidly that the fibers cannot perfectly 

 relax. 



It may be due to various causes: to drugs, as strychnine; to 

 bacterial poisoning through invasion of wounds ; or to disordered 

 conditions of the nerve system. It may be voluntary in char- 

 acter; when one deliberately stiffens the body or. any portion of 

 it the rigidity thus occurring is tetanic. 



Cramp is sudden involuntary contraction of muscle-fiber, 

 spasmodic in character and so violent as to be exceedingly painful. 



Convulsive movements or convulsions (spasms} are due to invol- 

 untary and forcible action of several muscles or groups of muscles. 

 The movements vary with the number of muscles involved. 



Fatigue of muscle tissue follows prolonged use, evidenced by 

 sensations of pain in the muscles themselves, probably due to an 

 accumulation of waste matters when the muscle is not quite equal 



