Flexor-rejiex evoked by a Single Break-shock. 115 



very thin wire, was inserted a millimetre or less into the skin of the dorsum 

 of one of the hind toes, and the wire brought to one binding screw of the 

 short circuit key of the secondary circuit, the wire from the copper plate 

 being brought to the other binding screw of the key. The stigmatic electrode 

 was made the kathode for the break-shock. The registration, etc., was as in 

 other experiments. 



The myograph records showed that, with break-shocks considerably above 

 threshold value, the reflex contraction was often of greater crest-height, as 

 well as of longer duration, than was the maximal twitch contraction evoked 

 from the motor nerve. The myogram of the break-shock reflex elicited 

 from the skin resembled that of the break-shock reflex evoked from the 

 bared skin nerve, e.g., musculocutaneous nerve, except that the skin reflex 

 tended to be somewhat less prolonged. 



5. In the spinal preparation, reflex contraction of tibialis anticus and other 

 flexor muscles of the limb is obtained from the ipsilateral afferent limb 

 nerves more readily than in the decerebrate preparations (7), and the reflex 

 contraction is more ample. In some of our experiments, we have taken 

 myograms of the tibialis anticus break-shock reflex in the decerebrate 

 condition, and then in the spinal condition, the spinal transection being 

 made either in the posterior thoracic region or in the anterior cervical. 

 Both with the low and the high spinal transection, the difference between the 

 decerebrate reflex and the spinal has been great (fig. 5). Very rarely has the 

 crest-height of the decerebrate reflex equalled that of the maximal twitch 

 evoked vid motor nerve. Often it has been less than half of that even with 

 break-shocks much higher on the inductorium scale than those sufficing for 

 the maximal twitch. In our experience, the break-shock reflex contraction 

 of tibialis anticus evoked from even the popliteal nerve in the decerebrate 

 condition gives a low relatively flat myogram of rather prolonged duration, 

 longer usually than that of the maximal twitch. The reflex provoked from 

 the same afferent nerve, and by a similar stimulus in the spinal preparation, 

 may have a crest-height four or five times that of the decerebrate reflex (6),(7). 

 This greater reflex response in the spinal, as compared with the decerebrate 

 preparation, is obvious immediately, e.g., ten minutes after spinal transection. 

 That it is, however, a release phenomenon rather than merely an irritative 

 excitation from the fresh trauma, is indicated by its persistence, not only for 

 many hours but for some days, to judge from the similar character of the 

 reflexes obtainable, when the cord had been cut, as in some of our experi- 

 ments, a week or more prior to the myographic examination. Also, the 

 threshold value of stimulus (break-shock) is higher, often far higher, in the 

 decerebrate (6), (7), than in the spinal condition (6), (7). Also, the upper 



VOL. XGII. — B. K 



