Reflexes, etc., of Mammalian Nerve-muscle. 255 



the two crest-heights are approximately equal, the time-relations of the 

 development and subsidence of tension are widely different. In no break- 

 shock reflex have I met decHne of tension in relation to crest-height so 

 rapidly precipitous as it is quite commonly in the " supra-maximal " motor- 

 nerve responses. Again, on the view that the tetanic character of the 

 reflex contraction evoked by a break-shock applied to the afferent nerve is 

 referable to repetitive reaction to the break-shock by the stimulated afferent 

 nerve-fibres themselves, the distribution of the repetitive process both in 

 time and among the individual nerve-fibres must be assumed to be con- 

 siderably different in the internal saphenous nerve from what it is in the 

 popliteal nerve ; the low prolonged break-shock reflex from the former 

 contrasts with the higher less plateau-like fountain-topped reflex contrac- 

 tion given by the latter. Again, the fact that the intensity and extent of 

 the break-shock reflex contraction is much greater in the spinal j) reparation 

 than in the decerebrate, a circumstance which affects the conditions of the 

 spinal centre but cannot be thought to influence that of the afferent nerve- 

 trunk itself at the seat of stimulation, argues for the centre rather than 

 the afferent nerve being responsible for the development of the tetanus 

 of the reflex response. 



On the other hand, if the motor nerve-fibres begin to respond repetitively 

 at high strength of the break-shock stimulus, it is prudent to suppose that so 

 also do the afferent fibres under similar strong stimuli. In this the results 

 endorse the opinion reached by Forbes and Gregg (4), who write after their 

 study of the nerve action-current, and their experience of the spread of reflex 

 activity to remote muscles in the decerebrate preparation : " Of the conceivable 

 explanations " . . " that have occurred to us, we incline to regard as the most 

 probable that a second propagated disturbance, or even a series of them, may 

 be evoked in each afferent nerve-fibre by a single shock, if sufficiently strong." 



Evidence of this may be looked for, in the present experiments, in some 

 change possibly discernible in the character of the reflex contraction on and 

 after the break-shock reaches about that strength at which it excites " supra- 

 maximal " contractions when applied direct to the motor nerve, i.e., at about 

 15 cm. on the scale of the inductorium used in these experiments. A change 

 in the form of the reflex myograms is in fact noticeable usually at about 

 this place on the inductorium scale. This change consists, as mentioned 

 earlier in the text, in a considerable further prolongation (fig. 7) in the 

 duration of the reflex contraction to the break-shock, accompanied by little or 

 no further increase in the crest-height, the reflex in its slow subsidence not 

 rarely exhibiting late subsidiary crests (fig. 4), assuming a somewhat dicrotic 

 or even tricrotic character. 



