SPINAL REFLEXES. 837 



even although all the afferent roots of the isolated length of cord have been 

 cut, and they are much less diminished by the root section than are tbe some- 

 what similar convulsions of strychnin poisoning. Contraction of the bladder 

 and erection of the hairs are among the spinal effects of asphyxia in the 

 mammal ; in strychnin convulsions, on the contrary, erection of the hairs in 

 my experience does not ensue ; the spinal origination of the asphyxial erection 

 is not, however, definitely proved. 



During the condition of apnoea the reflex convulsions characteristic of 

 strychnin and similar poisons do not, it is said, occur (Rosenthal and Leube, 

 Uspensky). 



(2) Drugs. — Some drugs affect the activity of the spinal centres, 

 certain of them greatly. Detailed account of their action lies beyond 

 the scope of this article. Besides depressants of protoplasmic activity 

 in general, e.g. chloroform, are certain alkaloids and salts, which 

 selectively depress, e.g. morphia, or exalt, e.g. strychnia, the spinal 

 centres. Material so unlike the normal constituents of nervous tissue 

 can hardly be supposed to yield fresh nervous force. The influence 

 must consist in facilitation of the discharge of force already latently 

 present, and the rendering of the liberating forces more effective, 

 tending to thwart inhibition. The action of strychnin on spinal nerve 

 cells is comparable with that of atropin on cardiac muscle cells. 



Influence of associated parts of the central organ — Inhibition 

 and facilitation ("Bahnung") of spinal reflexes. — The response made 

 by a reflex arc to an external stimulus is, as mentioned above, dependent 

 as much on the internal condition of the arc as on the external con- 

 ditions attaching to the stimulus. Reflex arcs, both lower and higher, 

 are inter-connected. The condition of any one is partly dependent on 

 the condition of many others. The nervous system is a unity ; in other 

 words, each even local reflex action is in truth a reaction to all sensi- 

 facient stimuli incident on the individual at the moment in sum both as 

 to space and as to past time. And those activities of the central nervous 

 system which are customarily considered autochthonous, have also, on 

 account of the inter-connection of the arcs, influence upon the reactions 

 of other arcs. The influence arising either way may take expression in 

 depression of the local reaction, e.g. the rendering a supraliminal stimulus 

 liminal or subliminal, or, in promotion of the local reaction, rendering a 

 previously subliminal stimulus liminal or supraliminal. The former 

 kind of effect has, since the Weber experiment on the cardiac vagus, 

 been known as " inhibition " (Hemmung, action moderateur), the latter 

 has, by Sigmund Exner, who has particularly studied it, been termed 

 " Bahnung" a felicitous expression not easily rendered into English. 1 



Inhibition of the heart's beat by excitation of the vagus nerve was 

 discovered by the Webers, and is described in Wagner's Dictionary of the 

 following year (1846). E. H. Weber forthwith extended the notion to the 

 cas*e of the increased spinal activity witnessed after ablation of the brain. 2 

 He suggested that removal of the brain removes a nervous mechanism 

 which inhibits the reflex spinal machinery. This notion of the inhibi- 

 tion of the activity of one part of the central nervous system by the 



1 Foster has rendered it by " augmentation," A. D. Waller by " canalisation," and the 

 word "reinforcement" has been a good deal used for some of the examples covered by 

 Exner's term. These three English terms are, however, not synonymous. " Facilitation " 

 perhaps most nearly expresses what is intended. 



2 Wagner's " Handwurterb. d. Physiol.," Braunschweig, 1846, Bd. iii. S. 47. Cf. 

 Volkmann, Arch. f. Anat., Physiol, v. icissensch. Med., 1838, S. 87. 



