562 Prof, C. 8. Sherrington. On Reciprocal [Aug. 10, 
VI. These reactions and the other accessory crossed ones dealt with above 
belong, evidently by the mode of their elicitation, to that class of reflexes which 
have been termed proprioceptive. By proprioceptive reflexes are meant 
reflex reactions excited habitually by the organism acting as agent upon itself 
through its own organs applied as stimuli to its own nerves. In proprioceptive 
reflexes the organism applies itself as a stimulus to itself. By its own act, and 
in its own substance, it excites one or more of its own receptor organs. Other 
reflexes—and they form the major part of reflex action—are excited by 
environmental change acting through some environmental medium which 
impinges directly on the receptors of the organism. But the case of, for 
instance, the bending of the knee, regarded as an exciting stimulus, is different 
from those. In it the organism, by executing a movement of a part of itself, 
supplies by the alteration of the condition of that part a stimulus to certain 
reflex arcs, proprioceptive arcs arising in that part. The reaction thus excited 
from these arcs is causally related less directly to the environment than are 
reflexes. excited immediately by the surrounding world; the proprioceptive 
reaction stands in secondary relation to an environmental cause. It is obvious 
that proprioceptive reflexes may be competent to extend and complete reflex 
actions, and cycles of reflex action, initiated primarily by environmental 
stimuli. They thus prolong, by intrinsic proprioceptive action, actions 
initiated by environmental stimuli of even transient operation. 
It was pointed out elsewhere* that proprioceptive reflexes tend to be 
characterised by certain features: (1) to be tonic; (2) to ally themselves with, 
and reinforce other reflexes, exteroceptive and interoceptive; (3) to restore a 
posture which a phasic reflex has disturbed, and thus to contribute toward 
reinstating a previous reflex equilibrium which had been departed from, ze., 
to be compensatory. The reactions described in this note bear out and 
illustrate these proprioceptive functions. They are tonic. They tend to 
ally themselves to other reflexes. Taking the case of the extensor of the 
knee, suppose some environmental stimulus, impinging on the standing 
animal, impels it to take a step. The flexor of the knee, thrown into con- 
traction, bends the knee; by so doing it stretches the knee-extensor and 
excites from it a proprioceptive reflex of relaxation (the “ lengthening 
reaction”), This proprioceptive reflex of the knee-extensor is adjuvant to 
the contraction of the knee-flexor. Then, the phase of knee-flexion having 
passed, the phase of knee-extension sets in (induced perhaps by successive 
spinal induction); the knee-extensor contracts and the knee-flexor ceases to 
contract. The contraction of the knee-extensor shortens the extensor muscle, 
* Sherrington, ‘Integrative Action of the Nervous System,’ London, 1906, chaps. 4 
and 9. 
