258 Break-shock Reflexes, etc., of Mammalian Nerve-muscle. 



process by the refractory period of the afferent or efferent fibres themselves. 

 In several respects it seems to me that the central " charge " process 

 suggests comparison with the " local excitatory process " of Adrian and Keith 

 Lucas, referred to above. In using for it the term central " charge " there is, 

 of course, no intention of implying to it the electrical attributions of that 

 term. 



Summary. 



The maximal twitch-contraction of tibialis anticus muscle (cat) evoked by 

 a single break-shock applied to the cut motor nerve is compared with the 

 same muscle's contraction as evoked reflexly (spinal preparation) by a single 

 break-shock applied to an afferent nerve. The reflex contraction is found 

 to exceed the former when the break-shock for the former is even con- 

 siderably weaker than that employed for the latter. Evidence is given that 

 this is due to the reflex response being tetanic in nature. If the break-shock 

 is, however, quite strong {i.e., above the limiting maximal value of Forbes 

 and Gregg) there is evidence that it excites even when applied to the motor 

 nerve a response of tetanic quality. The so-called " over-maximal twitch " 

 is in reality a response of this kind. Such responses are in this paper 

 termed " supra-maximal responses." 



Probability is shown that a reaction of like kind obtains in the afferent 

 nerve when the single-shock applied to it is of comparably high value. In 

 this latter case there is added to the tetanic reaction of the spinal centre a 

 tetanic reaction from afferent nerve fibres themselves. But with weak and 

 moderate break-shock stimuli the seat of origination of the tetanic character 

 of the reflex discharge appears to lie mainly, if not wholly, in the centre 

 itself. It is inferred that it arises there from a process, a " charge " process, 

 which is relatively long-lasting in comparison with the cycle of a nerve- 

 impulse, a process which is more intense and of longer duration when the 

 afferent fibres excited are many than when they are fewer. 



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