60 EXPERIMENTAL PHYSIOLOGY. 



Measure the diameter of the cups. 



(a) Is the total length of narcotic through which the impulse 

 passed greater in the case of the two small cups or of the one 

 large cup? 



(&) Which preparation ceased to respond first? 



(c) Does the result indicate that the impulse is extinguished 

 immediately in a narcotized region or by progressive decrement? 



(d) How do you reconcile decrement with the all or none 

 nature of conduction? 



(e) How does the intervening normal area between the two 

 short regions of narcosis affect the strength of the nerve impulse? 



(/) Does the energy of the impulse arise from the stimulus 

 or from the nerve fibre? 



(g) How does this experiment prove the all or none nature 

 of the nerve impulse? 



The passage from one step to another took place without 

 any contractions of intermediate size. Muscle fibres therefore 

 contract either not at all or to an extent which is nearly maxi- 

 mal. This is the all-or-none principle. According to this 

 principle when a muscle mass is giving a minimal or sub-maximal 

 contraction only a certain number of fibres is being called into 

 action, the rest remaining inactive. 



