474: MOVEMENTS. 



Although this view of the physiological action of the 

 muscular fibres is extremely probable, it cannot be assumed 

 that it has been absolutely demonstrated ; but it is certainly 

 more satisfactory and better sustained by experimental facts 

 than any theory that has hitherto been advanced. 



Mechanism of prolonged Muscular Contraction. By a 

 voluntary effort we are able to produce a muscular contrac- 

 tion of a certain duration, and of a power, within certain 

 limits, proportionate to the amount of force we may desire 

 to produce ; but after a certain time, the muscle becomes fa- 

 tigued, and it may become exhausted to the extent that it 

 will not respond to the normal stimulus. This is the kind 

 of muscular action most interesting to us as physiologists. 



The experiments of Marey seem to show precisely how 

 far the nervous action that gives rise to a powerful and con- 

 tinuous muscular contraction can be imitated by electricity. 

 Calling the movement produced by a single electric dis- 

 charge, secousse, which we have translated by the word 

 spasm, he calls the persistent contraction, tetanus. We will 

 adopt this name to distinguish persistent muscular action 

 from the single contraction that we have just described. 



It is a curious fact that a continued current of galvanic 

 electricity passed through a nerve or a muscle does not induce 

 muscular contraction; and it is only when the current is 

 closed or broken that any action is observed. But if we 

 employ statical electricity, a muscular spasm occurs at every 

 discharge, proportionate, in some degree, to the power of the 

 excitation. If the discharges be very frequently repeated, or 

 if a galvanic current be applied, broken by an interrupting 

 apparatus, the spasms follow each other in quick succession. 

 In experimenting upon the muscles of the frog with a regis- 

 tering apparatus, Marey has found that with a gradual 

 increase in the rapidity of the electric shocks, the individual 

 muscular spasms become less and less distinct, and that 

 finally the contraction is permanent. His diagrams show 



