1910.] Reversal of the Reflex Effect of an Afferent Ni erve. 487 
I. Intensity and form of electrical stimulation. 
With all forms of electric stimulus employed by us the stimulation, if it is 
to produce reflex contraction of the extensor muscle, must not be intense. 
This point is best dealt with when considering the influence of the form of 
the electric stimulus on the reflex result. As to this latter determinant 
factor, namely, the form of the electrical stimulus, our experience is that 
galvanic currents yield reflex contraction more readily than do faradic. 
(«) A constant galvanic current applied to the afferent nerve evokes reflex 
effect both at make and break. With ordinary strengths of current the 
result resembles the well-known du Bois Reymond formula for the effect 
of the current on the ordinary muscle-nerve preparation, inasmuch as there 
is obvious excitation of the nerve at make and break and not during 
the continued passage of the current. With the reflex preparation above 
described the effect at make and break when the current is of moderate or 
high strength is inhibition (fig. 1); when the current is quite weak the 
teflex effect may often be distinct though weak contraction both at make 
and break. Current direction and current strength and duration influence 
the du Bois Reymond formula in the reflex preparation as they do in the 
simple nerve-muscle préparation: we have studied these variations, but 
apart from the above general result. they bear little on the problem at hand, 
and we defer them for a fuller account. 
(@) Under stimulation of the afferent nerve by series of brief galvanic 
currents, ascending or descending, the reflex result on the tonic extensor 
muscle is in most cases contraction when the currents are quite weak, and 
is always inhibitory relaxation when the currents are quite strong (fig. 2). 
‘With intermediate strengths the result is a complex of the above; there is 
initial contraction, passing over into inhibition as the stimulus continues. 
The duration of the initial contraction is less, and the supervention of 
inhibition earlier as the intensity of the stimulus is progressively increased 
In successive stimulations. Even with weak stimulation the initial contrac- 
tion tends under prolonged application of the stimulus to give way and pass 
into inhibitory relaxation. 
(y) With faradic stimulation from the ordinary du Bois Reymond 
inductorium the results obtained are (fig. 3) somewhat similar to those just 
mentioned for galvanic currents. Weak stimulation tends to give some 
contraction, while moderate and strong stimulation always produces 
inhibitory relaxation. With the induced currents, however, the contraction 
is less readily developed than with the galvanic, and passes over into 
inhibition more speedily ; moreover, the contraction when obtained is more 
abrupt in onset and disappearance. With both forms of current, however, 
