Reflexes, etc., of Mammalian Nerve-muscle. 253 



Sometimes it did not occur even when 10 cm. was reached. These " supra- 

 maximal " contractions thus elicited from motor nerve appear from their 

 myogram features to be tetanic (fig. 6). They differ from the twitch in 

 their greater height and the greater steepness of up-gradient which their 

 ascent soon after its outset assumes, and, from the reflex contractions, 

 in their brief latency, their more peaked, less plateau-topped climax and 

 more rapidly falling, less prolonged, decline. Many of them cannot be 

 explained by mere addition to the kathodal (closing) twitch of a simple 

 opening twitch from anode, even supposing the intervention of the refractory 

 phase of the nerve-fibre did not disallow such an assumption. Their course 

 and character invite further examination, which I purpose to make. Their 

 interest here is for the indications they afford that a single break-shock stimulus 

 can, if of high strength, excite not merely one impulse, but a repetitive series 

 of impulses in fibres of a motor nerve {cf. Forbes and Gregg (4) ). 



The form of the " supra-maximal " responses, as they progressively increase 

 under successive increments of the break-shock stimulus, seems inadmissible 

 of other interpretation. As the secondary coil is by equal steps brought 

 nearer to the primary, the crest-height of the responses increases more and 

 more rapidly, as does, of course, the physical value of the induced current. 

 The development of contraction-tension thus reached by the higher members 

 of the ■'' supra-maximal " response series may amount to more than double 

 that of the ordinary maximal twitch. This seems explicable only by their 

 contraction being tetanic in nature. With the higher members of the 

 series, the latent period between stimulus and commencement of contraction 

 becomes remarkably shorter than that of the ordinary maximal twitch, 

 though the place of the electrodes be retained for both at the same distance 

 up the motor nerve. This led me to suspect at first that the strong current 

 employed might by escape be exciting the muscle itself directly, although 

 the distance between the muscle and the electrode the nearer to it was more 

 than 60 mm. But on ligating, with a thread soaked in normal saline, the 

 nerve 20 mm. distal to the electrodes, i.e., between muscle and the seat of 

 the electrodes on the nerve, all contraction in response to the strongest 

 break-shock given by the electrodes at once ceased. Moreover, strong 

 break-shocks applied to the afferent nerve show similarly no sign of 

 " escape," as evidenced by the latency of reaction being still as great as 

 with the weaker (fig. 5). 



It is difficult, in the light of Adrian's demonstration that the " all-or-none " 

 principle obtains in the impulse reaction of motor nerve-fibres, to suppose 

 that these strong stimuli given to the motor nerve can cause it to deliver 

 stronger nerve impulses to the neuro-myal junction or the muscle-fibres than 



