SPINAL REFLEXES. 



841 



mechanisms. The augmentor innervation of one muscle group seems regularly 

 to be accompanied by inhibition of the innervation of another muscle group \ 

 this mode of innervation I have termed "reciprocal." It seems a phenomenon 

 common in spinal reactions (see above, p. 820). 



In the spinal animal, inhibition due to excitation of a nerve path or centre 

 is usually quite transient, and passes over into exaltation even during the 

 continuance of the stimulation if that be fairly prolonged. This harmonises 

 with the alternating and phasic character general in muscular reactions from 

 the spinal animal. 



Rosenthal 1 insists on the longer latency of spinal reflexes evoked from 

 the skin of one hind-limb in the muscles of the other when the transection is 

 low than when high up. He found the reaction time for the above reflex in 

 the spinal frog not altered by sagittal median longitudinal section of the 

 crural region, but greatly lengthened by similar longitudinal section in the 

 brachial. Bickel,' 2 using a crossed hind-limb reflex, finds the reflex time in the 

 frog, salamander, and tortoise much greater when the cord has been transected 

 (days previously) just behind the brachial plexus than when at the bulbo-spinal 

 junction; after transection close anterior to the bulb, the reflex time is slightly 

 shorter than when at the bulbo-spinal junction, de Boeck 3 found in the rabbit 

 that stronger stimuli were necessary to excite movement by application to the 

 cord if the transection were below than if above the bulb. 



Exner 4 applied in the rabbit an electric stimulus to the cerebral 

 cortex at a point whose excitation caused contraction of a certain muscle 

 of the foot. The same muscle could also be caused to contract in 

 response to electric stimulation of a given strength applied to the skin of 

 the foot. When both cortex and skin were stimulated simultaneously, the 

 extent of the contraction was greater than when either was stimulated 

 alone. If the stimulus to the skin was so reduced that, alone, it was 

 subliminal for the reaction of the muscle, the cortical stimulus rendered 

 the skin stimulus efficient if applied at any interval less than about 

 three seconds after the cortical stimulus. The efficient skin stimulus 

 similarly rendered subliminal cortical stimuli efficient for a short 

 period. When both stimuli were, taken singly, subliminal, each 

 rendered the other subsequent one efficient throughout an interval 

 of about an eighth of a second. It is true that there is nothing to prove 

 in this experiment that the stimulus to the skin did not act md the 

 cortex, in which case the interaction was between two cortical reactions, 

 but the example even in that case serves by analogy to illustrate also 

 spinal reinforcement. 



Phenomena analogous to the " staircase " of contractions in cardiac and 

 skeletal muscle are met in spinal reactions. When examining reflexes 

 obtained from the afferent roots of the spinal animal, one often finds that, 

 after beginning the experiment by excitation of a given spinal root in a 

 limb region, the stimuli necessary being of a given strength, on returning 

 to the same root after having excited reflexes by a neighbouring root, the 

 strength of stimulus required has fallen to considerably lower than it had 

 been originally, and this happens under circumstances which seem to preclude 



1 Abliandl. d. Jc. Akad. d. Wissensch. zu Berlin, 1873 ; ibid. 1875 ; Sitzungsb. d. phys.- 

 med. Soc. zu Erlangen, 1873 ; Verhandl. d. Cong. f. innere Med., Wiesbaden, 1884 ; 

 Biol. Centralbl., Eiiangen, 1885 ; Mendelsohn, Sitzungsb. d. Jc. Akad. d. Wissensch., 

 Berlin, 1882; ibid., 1883; ibid., 1885; Rosenthal and Mendelsohn, Neurol. Centralbl., 

 Leipzig, 1897. 



2 Arch.f. d. ges. Physiol., Bonn, 1898, Bd. Ixx. 



3 Arch. f. Physiol. , Leipzig, 1887, S. 166; cf. also Owsjannikow, Arb. a. d. physiol. 

 Anst. zu Leipzig, 1874. 



4 Arch.f. d. ges. Physiol, Bonn, 1882, Bd. xxvii. 



