1910.| Reversal of the Reflex Effect of an Afferent Nerve. 445 
double effect obtainable from the opening muscle of the Astacus claw’ 
preparation ;* also the difference of result of infrequent, as compared with: 
frequent, stimuli applied to the distal sciatic nerve preparation when the: 
blood-volumet of the limb is observed—inhibitory dilatation resulting from: 
the former, vascular contraction and constriction from the latter, andi 
mixed results with intermediate rates. F. W. Frohlicht finds certain 
afferent nerves in the frog yield sometimes reflex excitation, sometimes reflex. 
inhibition, according to.the conditions of stimulus employed upon them. 
The case differs from the reversal of reflex effect studied by v. UexkullL,§: 
and by R. Magnus,|| inthe circumstance that in their reversals the stimulus. 
strength, etc., remain the same, and the changed condition is a central 
(R. Magnus) change brought about by alteration of posture, etc. Change: 
of posture at the knee in the isolated vasto-crureus preparation does not: 
indubitably influence the reversal we are dealing with in this paper. 
Thus, whether the knee is fully flexed, or fully extended, at the time 
when the stimulus is delivered, does not in our case clearly influence the 
reflex result (fig. 8); that result remains practically the same whatever 
the initial posture of the knee, i.c. whatever. the tonic lengths obtaining at 
the time in vasto-crureus. 
The case differs also from the reversal of reflex effect brought about by 
strychnine,** inasmuch as in the latter not only is no change in the 
intensity or mode of stimulation required, but also none in the posture, etc., 
of the reacting preparation. 
It is obvious that one way of accounting for the difference of reflex 
effect produced by varying the intensity and form of the stimulation of the 
afferent nerve is to assume the co-existence in the nerve of two different 
kinds of afferent nerve-fibres, exerting diametrically opposed reflex effects 
on the extensor muscle, and to suppose that of these nerve-fibres one kind 
is better. excited by weak inabrupt stimulation, and the other kind by abrupt 
and relatively intense stimulation. It appears to us premature, however, to 
accept unreservedly this hypothesis as a solution of the problem. 
* Richet, ‘ Archives de Physiologie,’ 1879, Paris; Biedermann, ‘Sitzungsb. d. k. k. 
Akad. d. Wiss.,’ Wien, 1887; Piotrowski; Fr. Frohlich, ‘Zeits. f. allgem. Physiol.,’ 
1908, vol. 7. 
t Bowditch and Warren, ‘ Journ. Physiol.,’ 1886, vol. 7, p. 32. 
{t ‘Zeits. f. allg. Physiol.,’ 1909, vol. 9, p. 85 ; also A. Tiedemann, 7bzd., 1910, vol. 10,, 
p. 196. 
§ ‘Zeitschr. f. Biol.,’ 1897, vol. 35. 
|| ‘ Pfltiger’s Archiv,’ 1910, vol. 125. 
I Lbid. 
** Sherrington, ‘ Roy. Soc. Proc.,’ B, 1905, vol. 76. 
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