444 Prof. C. S. Sherrington and Miss 8. C. M. Sowton. [Dec. 30, 
are proximal or distal on the nerve-trunk. If while the galvanic stimulation 
is eliciting a tonus reflex the faradic stimulus be applied, there results imme- 
diate reflex inhibition, which is recovered from when the faradic stimulus is 
withdrawn. 
It would appear, therefore, that the currents provided by the rotating 
rheonome act, when not too strong, as stimuli capable of exciting reflex tonus- 
contractions in the tonic extensor muscles of the decerebrate preparation. 
As to the actual character of the stimulus which is the source of the natural 
reflex tonus, e.g. in the decerebrate preparation, there is still little knowledge, 
except that it must be regarded as probably mechanical in kind. The fact 
that tonus reflexes not far dissimilar in outward features from natural tonus 
are obtainable by the above-described intermittent electric stimulation of 
the bared afferent nerve suggests that in the natural tonus itself the reaction 
of the afferent nerve is essentially rhythmic and intermittent, though the 
stimulus playing on its receptors may be constant, as is also the final 
mechanical result exhibited by the reacting muscle. 
There is much evidence in favour of the reflex extensor tonus of the 
decerebrate preparation being postural in meaning,* of that tonus being in 
fact the postural reflex executive of standing. In this connection it is 
interesting to note that a contralateral reflex usually accompanies the 
ipsilateral extensor contraction reflex above described, and that this contra- 
lateral reflex is, like the ipsilateral, a reflex extension of the limb. In this 
respect these ipsilateral extension reflexes provoked by electric stimuli 
resemble the ipsilateral extension reflex (the “extensor thrust ”) provocable 
by mechanical pressure on the planta. The fact that the tonic extension 
reflex elicited by weak galvanic currents is accompanied by concurrent 
extensor contraction in the contralateral fellow limb argues that the former 
reflex (ipsilateral extension) is not a part of the limb’s stepping reflex, 
because in stepping the two fellow limbs are always conversely instead of 
symmetrically moved. ! 
The afferent limb-nerves from which we have been able, by appropriate 
means, to elicit the reflex contraction of the ipsilateral extensor have been 
popliteal, plantar, peroneal, internal saphenous, obturator, and hamstring. 
We have found it more difficult to obtain the reflex from the hamstring 
nerve than from any of the others, and from the peroneal more difficult 
than from the popliteal. 3 
From these afferent nerves, therefore, two different reflex effects upon 
the tonic extensor muscle are obtainable, according as the stimulus 
employed for the afferent is weak or strong, &c. The case recalls the 
* Sherrington, ‘Journ. Physiol.’ 1910, vol. 40. 
