288 Prof. C. 8. Sherrington, [Apr. 17, 
phasic periods it can be seen that, starting from the phase in which it still 
evokes inhibition, little or perhaps not at all obviously less well than 
normally, its inhibitory effect then becomes progressively less, until it is 
replaced by excitation-effect (contraction) at first mild, later violent. This 
periodic phase will repeat itself many times. 
The conversion of inhibition effect as tested on the knee-extensor might 
be attributable to the afferent nerves stimulated containing two kinds of 
afferent fibres admixed, one kind causing reflex contraction of the muscle, the 
other kind reflex inhibition. Strychnine might, by augmenting the action of 
the former or by depressing the action of the latter, change the effect of 
stimulation of the mixed nerve. But the latter fibres would be expected to 
be associated in their action with—or, as urged above, to be even the self- 
same fibres which evoke—contraction of the flexor muscies. Now there is at 
the stage of strychninisation at which the change of inhibitory into 
excitatory effect occurs no trace of any paralysis or even depression of the 
flexor contractions. As is known, and was illustrated by tracings in a 
former paper,* the protagonist and the antagonist muscles are together 
thrown into synchronous contraction as an effect of strychnine. This and 
other considerations appear to me to weigh against explaining the con- 
version of inhibition-effect into excitation-effect by the hypothesis of reflex 
by antagonistic sets of fibres, oppositely poisoned centrally, commingled 
in these afferent nerves. It is certain, however, that as shown, the 
afferent nerves from the planta do contain, besides many fibres which 
evoke inhibition of the knee-extensor, some which can evoke under mechanical 
stimulation of the planta reflex contraction of the extensors of the knee. 
In the case of the other afferent nerves mentioned above, e.., the dorsal 
digitals, the hamstring nerve, the internal saphenous below the knee, the 
external saphenous, no evidence has ever been forthcoming that they 
contain any afferent fibres that can normally provoke any other effect on the 
knee-extensor than inhibition. Moreover, when a hamstring muscle is taken 
as the test-muscle, a similar conversion of inhibition into excitation 
(contraction) by strychnine is seen under the crossed extension reflex. 
This reflex, elicitable through the skin or various afferent nerves of the 
contralateral hind lhmb, normally excites the knee-extensor to contraction 
and inhibits the hamstrings, the knee-flexors. Under strychnine its reflex 
inhibition of the hamstring muscle is converted into reflex excitation (con- 
traction) of that muscle. In view of my observations as they stand at 
present, I incline to the inference that the action of the alkaloid is to convert 
* Sherrington, ‘ Journ. of Physiol.,’ vol. 13, 1892. . 
t ‘Roy. Soc. Proc.,’ vol. 66, p. 66, 1899; and ‘ Journ. of Physiol.,’ vol. 30, p. 39, 1903 
