MUSCULAR CONTRACTION. 5/ 



In ordinary voluntary contraction in man, the tone has a 

 vibration rate of from 38 to 40 per second. 



Under the influence of the arrow poison (curare), the 

 end-organs of the muscular nerves become incapable of 

 performing their function, so that the muscles of animals 

 poisoned by this drug are virtually nerveless. The con- 

 traction produced by instantaneous excitation, at any 

 point of a " curarized " and extended muscle, progresses 

 from the point excited in the direction of the fibres. In 

 fresh muscles the rate of progress of the contraction wave 

 is from 3 to 4 metres per second ; the duration of the 

 contraction is about O'O/ second ; hence the wave length of 

 contraction is about a quarter of a metre. In exhausted 

 muscles and in muscles under the influence of cold, the 

 rate of progress is slower than in fresh muscle at the 

 ordinary temperature. 



The above statements refer to the effects of single induction shocks, or of 

 successions of them. If a voltaic current is led for a moment through a 

 curarized muscle, the tissue is excited at the negative pole (cathode) at the 

 closure, and at the positive pole (anode) at the opening of the circuit. In 

 this case, the muscle remains contracted during the whole period that the 

 current is passing. 



By the term " absolute force" is denoted the heaviest 

 weight a muscle is able just to lift, when contracting to 

 the utmost advantage under the influence of a sufficient 

 excitation. The weight which a muscle is able to lift 

 varies according to its extension, being greatest when it is 

 most extended consequently greater at the beginning of 

 a tetanic or voluntary contraction than at the end. The 

 maximum quantity of work is done by a muscle when it 

 is nearly loaded to the utmost throughout the whole con- 

 traction. In order that this may be the case, the load and 

 the power of the muscle to lift it must diminish at the same 

 rate. If the load to be lifted remains constant, the muscle 

 acts most advantageously (i.e. does most work) when the 



