

1905.] On Reciprocal Innervation of Antagonistic Muscles. 287 
fibre is active, always produces excitation in certain efferent neurones, while 
another set of them when the nerve-fibre is active always normally produces 
inhibition of certain other efferent neurones, namely, those of the antagonistic 
muscles. The single afferent nerve-fibre would therefore be in regard to one 
set of its central terminal branches specifically excitor, and in regard to 
another set of its central endings specifically inhibitory. It will in this 
respect be duplex centrally. Such an inference agrees with an hypothesis 
which I have put forward before* regarding the mode of central termination 
of fibres producing this reciprocal effect. It suggests analogy between the 
structural arrangement for reflex reciprocal innervation and that of Astacus 
claw, if it be supposed that the individual nerve-fibres of the cray-fish claw 
preparation dichotomise, one division of the nerve-fibre passing to the 
opening muscle, the other division passing to the closing muscle; so that 
one division of the fibre exerts the excitor action, the other the well- — 
knowu inhibitory, studied by Richet,t Biedermann,} Piotrowski§ and others. 
The constancy of the reflex inhibition remarked above is a normal 
constancy, but it can be upset by abnormal change of the central condition of 
the cord. I find that exhibition of strychnine almost at once converts the 
inhibition into excitation, as also, more gradually, but just as potently, dves 
tetanus-toxin. This conversion sets in before and under smaller doses of 
strychnine or toxin than are required to produce the convulsive seizures 
characteristic of strychnine poisoning or general tetanus. 
This transformation of effect by strychnine holds good not only for the 
nerves above-mentioned but for skin stimuli, and also for those skin points 
remote from the hind limb itself, which nevertheless, as mentioned previously, 
provoke reflex inhibition of the test muscle. For instance in the case of the 
knee-extensor as test-muscle, the skin of the fore-paws. 
The conversion of inhibitory effect into excitation effect by strychnine is 
more easily obtained in the case of some nerves than of others. In the 
instances of the nerves above-mentioned the conversion is least facile, 2.¢., 
requires larger doses or longer time for development, in the case of the 
hamstring nerve than in the others. The inhibitory effect belonging to that 
nerve is readily lessened by the strychnine, but its actual replacement by 
excitation-effect, eg., contraction of knee-extensor, not only requires larger 
doses of strychnine but is even then phasic rather than continuous. When this 
nerve is tested by stimulation at regular short intervals during one of these 
* Sherrington, ‘Text-book of Physiology,’ edited by Schafer, vol. 2, 1900; cf. also 
H. E. Hering, ‘ Ergebnisse der Physiologie,’ I, 1902. 
+ ‘ Physiol. des Muscles et des Nerfs,’ p. 274, 1882. 
{ ‘Sitzungsb. d. Wiener Akad.,’ vol. 95, 3, p. 8, 1887. 
§ ‘Journ. of Physiol.,’ vol. 14, 1893. 
