88 MUSCLE. 



the latent period and the stage of contraction consume only about 

 one-tenth each. 



What is tetanus ? 



When the stimuli follow one another in rapid succession the con- 

 tractions are practically constant, and the stage of elongation does 

 not follow. This condition is known as tetanus. The stimuli may 

 be slow enough to allow perceptible quivering of the muscle (and 

 a wavy tracing of the myogram), or may be very rapid, so as to 

 keep the contraction constant. 



What effect has fatigue upon the muscle ? 



Its latent period is longer and the strength of the contractions 

 diminish. 



Is the temperature of muscle elevated by action ? 



Yes. It has been estimated that the temperature of the biceps 

 muscle may be elevated one to two degrees of the Fahrenheit scale 

 by exercise. It is not known whether this is due to chemical 

 action or to friction between the fibres. 



How does the shape of the muscle change in contraction ? 



The muscle becomes shorter, thicker, and harder, and seems to 

 bulge at the centre. This is not an actual increase in bulk, for 

 what is gained in thickness is made up in the loss by shortening. 

 Each fibre of the muscle contracts and becomes short and thick, 

 as does the whole muscle. This shortening is due to an approxi- 

 mation of the elements probably, and not to a change in the 

 arrangement of the elements. 



What chemical changes occur in muscle with action? 



The muscle (in rest alkaline) becomes acid from the develop- 

 ment of lactic acid, and there is found a kind of glucose known as 

 inosite, or " muscle-sugar." Besides this, the active metabolism 

 increases the production of carbonic acid and of extractives. 



What is rigor mortis ? 



When a muscle is dead it will no longer respond to stimuli, but 

 remains in a contracted state, fixing the limbs and body in rigid 

 condition. This post-mortem rigidity constitutes rigor mortis. 

 The muscles of the neck and jaw are usually first affected, and 



