NERVE. 57 



The necessity for oxygen is a further indication of increased meta- 

 bolism during activity. Nevertheless, nerve must use an infini- 

 tesimal amount of energy in its work, not only in view of the above 

 considerations, but because it is very difficult to fatigue. 



A nerve has been stimulated continuously for ten hours and 



still transmitted impulses, as could be shown by a galvanometer 



or by preventing the fatigue of the muscle which is done by blocking 



the contraction with curare, cold or a narcotic. Then at the end 



of the time, the block being removed, the muscle contracted. 



Experiment 26. The Resistance of Nerve to Fatigue. 



Arrange two nerve muscle preparations so that they support 



levers in such a position that they can write one above the 



other upon the same drum. Both nerves are to lie side by side 



on the same pair of electrodes. Abolish the conductivity of 



one nerve by keeping it moistened with ether. Keep the nerve 



moist by improvising a moist chamber from filter paper. 



Stimulate the nerves by means of a tetanizing current and 



obtain a record of the contraction upon a slowly moving drum. 



If sufficient ether is used the muscle on that side should not 



contract. As soon as this stage is reached, tetanize both 



nerves until the active muscle is exhausted. When this stage 



is reached, wash away the ether, with iso tonic NaCl solution, 



continuing the stimulation. The muscle upon the treated side 



should soon begin to contract. 



It can be shown further that the fatigued muscle will 

 respond by direct stimulation. Therefore if nerve fibres are 

 still carrying impulses as is shown by response of the other 

 muscle, the seat of fatigue must be between nerve fibre and 

 muscle fibre, or at the end plate. The end plate according to this 

 becomes fatigued much earlier than the muscle fibre and thus 

 saves the fibre from excessive fatigue. 



THE ALL-OR-NONE PRINCIPLE IN NERVE AND MUSCLE. 



Stimulation of a muscle either directly or through its nerve pro- 

 duces a step-like increase in response, when successively increasing 

 stimuli are used. When once a step has been established further 

 increase of the stimulus causes no increase of contraction until a 

 new step is reached. The maximum contraction of the whole 



