162 Prof. C. 8. Sherrington. [Feb. 28, 
presents resemblance to peripheral inhibition as exemplified, for instance 
by pure vagus action on the heart. The cardiac depression is followed by 
exaltation of excitability and conductivity of the cardiac tissue. “As to 
contraction force and conductivity, the after-effect is in the opposite direction 
to the primary effect.”* — 
This spinal interaction between certain reflex centres, related to move- 
ments of opposed direction, resembles that known to hold between adjacent 
retinal points. The spinal phenomenon seems fundamentally akin to that 
of visual contrast,f as both Macdougall and myself have pointed out. If 
visual brightness be regarded as analogous to the activity of spinal discharge, 
and visual darkness analogous to the absence of spinal discharge, the 
reciprocal spinal action in the example last mentioned above has a close 
counterpart in the well-known experiment where a white disc used as a 
prolonged stimulus leaves as after-effect in the visual field a grey image 
surrounded by a bright ring (Hering’s “ Lichthof”). The bright ring has 
for its spinal equivalent the “spontaneous” discharge from the adjacent 
reciprocally correlated spinal “ centre.’t 
The “spinal induction” is obviously qualified to play a part in linking 
reflexes together in a co-ordinate sequence of successive combination. If a 
reflex are A during its own activity not only temporarily checks the 
discharge-action of an opposed reflex arc B, but also as a subsequent result 
induces in arc B a phase of greater excitability and capacity for discharge, it 
predisposes the spinal organ for a second reflex opposite in character to its 
own in immediate succession to itself. I have previously pointed out the 
peculiar prominence of “alternating reflexes ”§ in prolonged spinal reactions. 
These may be traceable largely to “spinal induction.” It is significant that 
they are usually cut short with ease by mere passive mechanical interruption 
of the alternating movement in progress. 
Much of the reflex action of the limb that can be studied in the “ spinal” 
dog bears the character of adaptation to locomotion. This has been shown 
recently with particular clearness by the observations of Philippson.|| In 
* Gaskell, ‘Schafer’s Text-book of Physiology,’ vol. 2, p. 220, 1900 ; see also ‘ Transact. 
of VIIIth Internat. Med. Congress,’ Copenhagen, 1884. 
+ Sherrington, ‘Journal of Physiol.,’ vol. 21, p, 33, 1897 ; Macdougall, ‘ Brain,’ vol. 26, 
p- 177, 1908. . 
{t For the influence of varying conditions on this experiment and an explanation 
offered important to the analogy suggested here, see W. Macdougall, ‘‘ Young’s Theory 
of Light and Colour Vision,” ‘ Mind,’ vol. 10, N.S., No. 37, pp. 25 to 30 of the reprint. 
§ Croonian Lecture, 1897 ; ‘ Phil. Trans.,’ B, 1898. 
|| ‘ Archives de Physiologie,’ 1904. 
